//! Frame render and metadata API.

use std::{marker::PhantomData, mem, sync::Arc};

use crate::{
    widget::info::{ParallelSegmentOffsets, WidgetBoundsInfo},
    window::WINDOW,
};
use zng_color::{
    colors,
    filter::RenderFilter,
    gradient::{RenderExtendMode, RenderGradientStop},
    RenderMixBlendMode, Rgba,
};
use zng_layout::unit::{
    euclid, AngleRadian, Factor, FactorUnits, Px, PxCornerRadius, PxLine, PxPoint, PxRect, PxSideOffsets, PxSize, PxTransform, PxVector,
};
use zng_task::rayon::iter::{ParallelBridge, ParallelIterator};
use zng_unique_id::{impl_unique_id_bytemuck, unique_id_32};
use zng_var::{impl_from_and_into_var, Var, VarCapability, VarValue};
use zng_view_api::{
    api_extension::{ApiExtensionId, ApiExtensionPayload},
    config::FontAntiAliasing,
    display_list::{DisplayList, DisplayListBuilder, FilterOp, NinePatchSource, ReuseStart},
    font::{GlyphInstance, GlyphOptions},
    window::FrameId,
    ReferenceFrameId as RenderReferenceFrameId, ViewProcessGen,
};

use crate::{
    update::{RenderUpdates, UpdateFlags},
    view_process::ViewRenderer,
    widget::{
        base::{Parallel, PARALLEL_VAR},
        border::{self, BorderSides},
        info::{HitTestClips, ParallelBuilder, WidgetInfo, WidgetInfoTree, WidgetRenderInfo},
        WidgetId, WIDGET,
    },
};

pub use zng_view_api::{
    display_list::{FrameValue, FrameValueUpdate, ReuseRange},
    ImageRendering, RepeatMode, TransformStyle,
};

/// A text font.
///
/// This trait is an interface for the renderer into the font API used in the application.
pub trait Font {
    /// Gets if the font is the fallback that does not have any glyph.
    fn is_empty_fallback(&self) -> bool;

    /// Gets the instance key in the `renderer` namespace.
    ///
    /// The font configuration must be provided by `self`, except the `synthesis` that is used in the font instance.
    fn renderer_id(&self, renderer: &ViewRenderer, synthesis: FontSynthesis) -> zng_view_api::font::FontId;
}

/// A loaded or loading image.
///
/// This trait is an interface for the renderer into the image API used in the application.
///
/// The ideal image format is BGRA with pre-multiplied alpha.
pub trait Img {
    /// Gets the image ID in the `renderer` namespace.
    ///
    /// The image must be loaded asynchronously by `self` and does not need to
    /// be loaded yet when the key is returned.
    fn renderer_id(&self, renderer: &ViewRenderer) -> zng_view_api::image::ImageTextureId;

    /// Returns a value that indicates if the image is already pre-multiplied.
    ///
    /// The faster option is pre-multiplied, that is also the default return value.
    fn alpha_type(&self) -> zng_view_api::AlphaType {
        zng_view_api::AlphaType::PremultipliedAlpha
    }
}

macro_rules! expect_inner {
    ($self:ident.$fn_name:ident) => {
        if $self.is_outer() {
            tracing::error!("called `{}` in outer context of `{}`", stringify!($fn_name), $self.widget_id);
        }
    };
}

macro_rules! warn_empty {
    ($self:ident.$fn_name:ident($rect:tt)) => {
        #[cfg(debug_assertions)]
        if $rect.is_empty() {
            tracing::warn!(
                "called `{}` with empty `{:?}` in `{:?}`",
                stringify!($fn_name),
                $rect,
                $self.widget_id
            )
        }
    };
}

struct WidgetData {
    parent_child_offset: PxVector,
    inner_is_set: bool, // used to flag if frame is always 2d translate/scale.
    inner_transform: PxTransform,
    filter: RenderFilter,
    blend: RenderMixBlendMode,
    backdrop_filter: RenderFilter,
}

/// A full frame builder.
pub struct FrameBuilder {
    render_widgets: Arc<RenderUpdates>,
    render_update_widgets: Arc<RenderUpdates>,

    frame_id: FrameId,
    widget_id: WidgetId,
    transform: PxTransform,
    transform_style: TransformStyle,

    default_font_aa: FontAntiAliasing,

    renderer: Option<ViewRenderer>,

    scale_factor: Factor,

    display_list: DisplayListBuilder,

    hit_testable: bool,
    visible: bool,
    backface_visible: bool,
    auto_hit_test: bool,
    hit_clips: HitTestClips,

    perspective: Option<(f32, PxPoint)>,

    auto_hide_rect: PxRect,
    widget_data: Option<WidgetData>,
    child_offset: PxVector,
    parent_inner_bounds: Option<PxRect>,

    view_process_has_frame: bool,
    can_reuse: bool,
    open_reuse: Option<ReuseStart>,

    clear_color: Option<Rgba>,

    widget_count: usize,
    widget_count_offsets: ParallelSegmentOffsets,

    debug_dot_overlays: Vec<(PxPoint, Rgba)>,
}
impl FrameBuilder {
    /// New builder.
    ///
    /// * `render_widgets` - External render requests.
    /// * `render_update_widgets` - External render update requests.
    ///
    /// * `frame_id` - Id of the new frame.
    /// * `root_id` - Id of the window root widget.
    /// * `root_bounds` - Root widget bounds info.
    /// * `info_tree` - Info tree of the last frame.
    /// * `renderer` - Connection to the renderer that will render the frame, is `None` in renderless mode.
    /// * `scale_factor` - Scale factor that will be used to render the frame, usually the scale factor of the screen the window is at.
    /// * `default_font_aa` - Fallback font anti-aliasing used when the default value is requested.
    /// because WebRender does not let us change the initial clear color.
    #[allow(clippy::too_many_arguments)]
    pub fn new(
        render_widgets: Arc<RenderUpdates>,
        render_update_widgets: Arc<RenderUpdates>,
        frame_id: FrameId,
        root_id: WidgetId,
        root_bounds: &WidgetBoundsInfo,
        info_tree: &WidgetInfoTree,
        renderer: Option<ViewRenderer>,
        scale_factor: Factor,
        default_font_aa: FontAntiAliasing,
    ) -> Self {
        let display_list = DisplayListBuilder::new(frame_id);

        let root_size = root_bounds.outer_size();
        let auto_hide_rect = PxRect::from_size(root_size).inflate(root_size.width, root_size.height);
        root_bounds.set_outer_transform(PxTransform::identity(), info_tree);

        let gen = renderer
            .as_ref()
            .and_then(|r| r.generation().ok())
            .unwrap_or(ViewProcessGen::INVALID);
        let view_process_has_frame = gen != ViewProcessGen::INVALID && gen == info_tree.view_process_gen();

        FrameBuilder {
            render_widgets,
            render_update_widgets,
            frame_id,
            widget_id: root_id,
            transform: PxTransform::identity(),
            transform_style: TransformStyle::Flat,
            default_font_aa: match default_font_aa {
                FontAntiAliasing::Default => FontAntiAliasing::Subpixel,
                aa => aa,
            },
            renderer,
            scale_factor,
            display_list,
            hit_testable: true,
            visible: true,
            backface_visible: true,
            auto_hit_test: false,
            hit_clips: HitTestClips::default(),
            widget_data: Some(WidgetData {
                filter: vec![],
                blend: RenderMixBlendMode::Normal,
                backdrop_filter: vec![],
                parent_child_offset: PxVector::zero(),
                inner_is_set: false,
                inner_transform: PxTransform::identity(),
            }),
            child_offset: PxVector::zero(),
            parent_inner_bounds: None,
            perspective: None,
            view_process_has_frame,
            can_reuse: view_process_has_frame,
            open_reuse: None,
            auto_hide_rect,

            widget_count: 0,
            widget_count_offsets: ParallelSegmentOffsets::default(),

            clear_color: Some(colors::BLACK.transparent()),

            debug_dot_overlays: vec![],
        }
    }

    /// [`new`](Self::new) with only the inputs required for renderless mode.
    #[allow(clippy::too_many_arguments)]
    pub fn new_renderless(
        render_widgets: Arc<RenderUpdates>,
        render_update_widgets: Arc<RenderUpdates>,
        frame_id: FrameId,
        root_id: WidgetId,
        root_bounds: &WidgetBoundsInfo,
        info_tree: &WidgetInfoTree,
        scale_factor: Factor,
        default_font_aa: FontAntiAliasing,
    ) -> Self {
        Self::new(
            render_widgets,
            render_update_widgets,
            frame_id,
            root_id,
            root_bounds,
            info_tree,
            None,
            scale_factor,
            default_font_aa,
        )
    }

    /// Pixel scale factor used by the renderer.
    ///
    /// All layout values are scaled by this factor in the renderer.
    pub fn scale_factor(&self) -> Factor {
        self.scale_factor
    }

    /// If is building a frame for a headless and renderless window.
    ///
    /// In this mode only the meta and layout information will be used as a *frame*.
    pub fn is_renderless(&self) -> bool {
        self.renderer.is_none()
    }

    /// Set the color used to clear the pixel frame before drawing this frame.
    ///
    /// Note the default clear color is `rgba(0, 0, 0, 0)`, and it is not retained, a property
    /// that sets the clear color must set it every render.
    ///
    /// Note that the clear color is always *rendered* first before all other layers, if more then
    /// one layer sets the clear color only the value set on the top-most layer is used.
    pub fn set_clear_color(&mut self, color: Rgba) {
        self.clear_color = Some(color);
    }

    /// Connection to the renderer that will render this frame.
    ///
    /// Returns `None` when in [renderless](Self::is_renderless) mode.
    pub fn renderer(&self) -> Option<&ViewRenderer> {
        self.renderer.as_ref()
    }

    /// Id of the new frame.
    pub fn frame_id(&self) -> FrameId {
        self.frame_id
    }

    /// Id of the current widget context.
    pub fn widget_id(&self) -> WidgetId {
        self.widget_id
    }

    /// Current transform.
    pub fn transform(&self) -> &PxTransform {
        &self.transform
    }

    /// Returns `true` if hit-testing is enabled in the widget context, if `false` methods that push
    /// a hit-test silently skip.
    ///
    /// This can be set to `false` in a context using [`with_hit_tests_disabled`].
    ///
    /// [`with_hit_tests_disabled`]: Self::with_hit_tests_disabled
    pub fn is_hit_testable(&self) -> bool {
        self.hit_testable
    }

    /// Returns `true` if display items are actually generated, if `false` only transforms and hit-test are rendered.
    pub fn is_visible(&self) -> bool {
        self.visible
    }

    /// Returns `true` if hit-tests are automatically pushed by `push_*` methods.
    ///
    /// Note that hit-tests are only added if [`is_hit_testable`] is `true`.
    ///
    /// [`is_hit_testable`]: Self::is_hit_testable
    pub fn auto_hit_test(&self) -> bool {
        self.auto_hit_test
    }

    /// Runs `render` with `aa` used as the default text anti-aliasing mode.
    pub fn with_default_font_aa(&mut self, aa: FontAntiAliasing, render: impl FnOnce(&mut Self)) {
        let parent = mem::replace(&mut self.default_font_aa, aa);
        render(self);
        self.default_font_aa = parent;
    }

    /// Runs `render` with hit-tests disabled, inside `render` [`is_hit_testable`] is `false`, after
    /// it is the current value.
    ///
    /// [`is_hit_testable`]: Self::is_hit_testable
    pub fn with_hit_tests_disabled(&mut self, render: impl FnOnce(&mut Self)) {
        let prev = mem::replace(&mut self.hit_testable, false);
        render(self);
        self.hit_testable = prev;
    }

    /// Runs `render` with [`auto_hit_test`] set to a value for the duration of the `render` call.
    ///
    /// If this is used, [`FrameUpdate::with_auto_hit_test`] must also be used.
    ///
    /// [`auto_hit_test`]: Self::auto_hit_test
    pub fn with_auto_hit_test(&mut self, auto_hit_test: bool, render: impl FnOnce(&mut Self)) {
        let prev = mem::replace(&mut self.auto_hit_test, auto_hit_test);
        render(self);
        self.auto_hit_test = prev;
    }

    /// Current culling rect, widgets with outer-bounds that don't intersect this rect are rendered [hidden].
    ///
    /// [hidden]: Self::hide
    pub fn auto_hide_rect(&self) -> PxRect {
        self.auto_hide_rect
    }

    /// Runs `render` and [`hide`] all widgets with outer-bounds that don't intersect with the `auto_hide_rect`.
    ///
    /// [`hide`]: Self::hide
    pub fn with_auto_hide_rect(&mut self, auto_hide_rect: PxRect, render: impl FnOnce(&mut Self)) {
        let parent_rect = mem::replace(&mut self.auto_hide_rect, auto_hide_rect);
        render(self);
        self.auto_hide_rect = parent_rect;
    }

    /// Start a new widget outer context, this sets [`is_outer`] to `true` until an inner call to [`push_inner`],
    /// during this period properties can configure the widget stacking context and actual rendering and transforms
    /// are discouraged.
    ///
    /// If the widget has been rendered before, render was not requested for it and [`can_reuse`] allows reuse, the `render`
    /// closure is not called, an only a reference to the widget range in the previous frame is send.
    ///
    /// If the widget is collapsed during layout it is not rendered. See [`WidgetLayout::collapse`] for more details.
    ///
    /// [`is_outer`]: Self::is_outer
    /// [`push_inner`]: Self::push_inner
    /// [`can_reuse`]: Self::can_reuse
    /// [`WidgetLayout::collapse`]: crate::widget::info::WidgetLayout::collapse
    pub fn push_widget(&mut self, render: impl FnOnce(&mut Self)) {
        let wgt_info = WIDGET.info();
        let id = wgt_info.id();

        #[cfg(debug_assertions)]
        if self.widget_data.is_some() && WIDGET.parent_id().is_some() {
            tracing::error!(
                "called `push_widget` for `{}` without calling `push_inner` for the parent `{}`",
                WIDGET.trace_id(),
                self.widget_id
            );
        }

        let bounds = wgt_info.bounds_info();
        let tree = wgt_info.tree();

        if bounds.is_collapsed() {
            // collapse
            for info in wgt_info.self_and_descendants() {
                info.bounds_info().set_rendered(None, tree);
            }
            // LAYOUT can be pending if parent called `collapse_child`, cleanup here.
            let _ = WIDGET.take_update(UpdateFlags::LAYOUT | UpdateFlags::RENDER | UpdateFlags::RENDER_UPDATE);
            let _ = WIDGET.take_render_reuse(&self.render_widgets, &self.render_update_widgets);
            return;
        } else {
            #[cfg(debug_assertions)]
            if WIDGET.pending_update().contains(UpdateFlags::LAYOUT) {
                // pending layout requested from inside the widget should have updated before render,
                // this indicates that a widget skipped layout without properly collapsing.
                tracing::error!("called `push_widget` for `{}` with pending layout", WIDGET.trace_id());
            }
        }

        let mut try_reuse = true;

        let prev_outer = bounds.outer_transform();
        let outer_transform = PxTransform::from(self.child_offset).then(&self.transform);
        bounds.set_outer_transform(outer_transform, tree);

        if bounds.parent_child_offset() != self.child_offset {
            bounds.set_parent_child_offset(self.child_offset);
            try_reuse = false;
        }
        let outer_bounds = bounds.outer_bounds();

        let parent_visible = self.visible;

        if bounds.can_auto_hide() {
            // collapse already handled, don't hide empty bounds here
            // the bounds could be empty with visible content still,
            // for example a Preserve3D object rotated 90º with 3D children also rotated.
            let mut outer_bounds = outer_bounds;
            if outer_bounds.size.width < Px(1) {
                outer_bounds.size.width = Px(1);
            }
            if outer_bounds.size.height < Px(1) {
                outer_bounds.size.height = Px(1);
            }
            match self.auto_hide_rect.intersection(&outer_bounds) {
                Some(cull) => {
                    let partial = cull != outer_bounds;
                    if partial || bounds.is_partially_culled() {
                        // partial cull, cannot reuse because descendant vis may have changed.
                        try_reuse = false;
                        bounds.set_is_partially_culled(partial);
                    }
                }
                None => {
                    // full cull
                    self.visible = false;
                }
            }
        } else {
            bounds.set_is_partially_culled(false);
        }

        let parent_perspective = self.perspective;
        self.perspective = wgt_info.perspective();
        if let Some((_, o)) = &mut self.perspective {
            *o -= self.child_offset;
        }

        let can_reuse = self.view_process_has_frame
            && match bounds.render_info() {
                Some(i) => i.visible == self.visible && i.parent_perspective == self.perspective,
                // cannot reuse if the widget was not rendered in the previous frame (clear stale reuse ranges in descendants).
                None => false,
            };
        let parent_can_reuse = mem::replace(&mut self.can_reuse, can_reuse);

        try_reuse &= can_reuse;

        self.widget_count += 1;
        let widget_z = self.widget_count;

        let mut reuse = WIDGET.take_render_reuse(&self.render_widgets, &self.render_update_widgets);
        if !try_reuse {
            reuse = None;
        }

        let mut undo_prev_outer_transform = None;
        if reuse.is_some() {
            // check if is possible to reuse.
            if let Some(undo_prev) = prev_outer.inverse() {
                undo_prev_outer_transform = Some(undo_prev);
            } else {
                reuse = None; // cannot reuse because cannot undo prev-transform.
            }
        }

        let index = self.hit_clips.push_child(id);
        bounds.set_hit_index(index);

        let mut reused = true;
        let display_count = self.display_list.len();

        let child_offset = mem::take(&mut self.child_offset);

        // try to reuse, or calls the closure and saves the reuse range.
        self.push_reuse(&mut reuse, |frame| {
            // did not reuse, render widget.

            reused = false;
            undo_prev_outer_transform = None;

            frame.widget_data = Some(WidgetData {
                filter: vec![],
                blend: RenderMixBlendMode::Normal,
                backdrop_filter: vec![],
                parent_child_offset: child_offset,
                inner_is_set: frame.perspective.is_some(),
                inner_transform: PxTransform::identity(),
            });
            let parent_widget = mem::replace(&mut frame.widget_id, id);

            render(frame);

            frame.widget_id = parent_widget;
            frame.widget_data = None;
        });

        WIDGET.set_render_reuse(reuse);

        if reused {
            // if did reuse, patch transforms and z-indexes.

            let _span = tracing::trace_span!("reuse-descendants", ?id).entered();

            let transform_patch = undo_prev_outer_transform.and_then(|t| {
                let t = t.then(&outer_transform);
                if t != PxTransform::identity() {
                    Some(t)
                } else {
                    None
                }
            });

            let current_wgt = tree.get(id).unwrap();
            let z_patch = widget_z as i64 - current_wgt.z_index().map(|(b, _)| b.0 as i64).unwrap_or(0);

            let update_transforms = transform_patch.is_some();
            let seg_id = self.widget_count_offsets.id();

            // apply patches, only iterates over descendants once.
            if update_transforms {
                let transform_patch = transform_patch.unwrap();

                // patch descendants outer and inner.
                let update_transforms_and_z = |info: WidgetInfo| {
                    let b = info.bounds_info();

                    if b != bounds {
                        // only patch outer of descendants
                        b.set_outer_transform(b.outer_transform().then(&transform_patch), tree);
                    }
                    b.set_inner_transform(
                        b.inner_transform().then(&transform_patch),
                        tree,
                        info.id(),
                        info.parent().map(|p| p.inner_bounds()),
                    );

                    if let Some(i) = b.render_info() {
                        let (back, front) = info.z_index().unwrap();
                        let back = back.0 as i64 + z_patch;
                        let front = front.0 as i64 + z_patch;

                        b.set_rendered(
                            Some(WidgetRenderInfo {
                                visible: i.visible,
                                parent_perspective: i.parent_perspective,
                                seg_id,
                                back: back.try_into().unwrap(),
                                front: front.try_into().unwrap(),
                            }),
                            tree,
                        );
                    }
                };

                let targets = current_wgt.self_and_descendants();
                if PARALLEL_VAR.get().contains(Parallel::RENDER) {
                    targets.par_bridge().for_each(update_transforms_and_z);
                } else {
                    targets.for_each(update_transforms_and_z);
                }
            } else {
                let update_z = |info: WidgetInfo| {
                    let bounds = info.bounds_info();

                    if let Some(i) = bounds.render_info() {
                        let (back, front) = info.z_index().unwrap();
                        let mut back = back.0 as i64 + z_patch;
                        let mut front = front.0 as i64 + z_patch;
                        if back < 0 {
                            tracing::error!("incorrect back Z-index ({back}) after patch ({z_patch})");
                            back = 0;
                        }
                        if front < 0 {
                            tracing::error!("incorrect front Z-index ({front}) after patch ({z_patch})");
                            front = 0;
                        }
                        bounds.set_rendered(
                            Some(WidgetRenderInfo {
                                visible: i.visible,
                                parent_perspective: i.parent_perspective,
                                seg_id,
                                back: back as _,
                                front: front as _,
                            }),
                            tree,
                        );
                    }
                };

                let targets = current_wgt.self_and_descendants();
                if PARALLEL_VAR.get().contains(Parallel::RENDER) {
                    targets.par_bridge().for_each(update_z);
                } else {
                    targets.for_each(update_z);
                }
            }

            // increment by reused
            self.widget_count = bounds.render_info().map(|i| i.front).unwrap_or(self.widget_count);
        } else {
            // if did not reuse and rendered
            bounds.set_rendered(
                Some(WidgetRenderInfo {
                    visible: self.display_list.len() > display_count,
                    parent_perspective: self.perspective,
                    seg_id: self.widget_count_offsets.id(),
                    back: widget_z,
                    front: self.widget_count,
                }),
                tree,
            );
        }

        self.visible = parent_visible;
        self.perspective = parent_perspective;
        self.can_reuse = parent_can_reuse;
    }

    /// If previously generated display list items are available for reuse.
    ///
    /// If `false` widgets must do a full render using [`push_widget`] even if they did not request a render.
    ///
    /// [`push_widget`]: Self::push_widget
    pub fn can_reuse(&self) -> bool {
        self.can_reuse
    }

    /// Calls `render` with [`can_reuse`] set to `false`.
    ///
    /// [`can_reuse`]: Self::can_reuse
    pub fn with_no_reuse(&mut self, render: impl FnOnce(&mut Self)) {
        let prev_can_reuse = self.can_reuse;
        self.can_reuse = false;
        render(self);
        self.can_reuse = prev_can_reuse;
    }

    /// If `group` has a range and [`can_reuse`] a reference to the items is added, otherwise `generate` is called and
    /// any display items generated by it are tracked in `group`.
    ///
    /// Note that hit-test items are not part of `group`, only display items are reused here, hit-test items for a widget are only reused if the entire
    /// widget is reused in [`push_widget`]. This method is recommended for widgets that render a large volume of display data that is likely to be reused
    /// even when the widget itself is not reused, an example is a widget that renders text and a background, the entire widget is invalidated when the
    /// background changes, but the text is the same, so placing the text in a reuse group avoids having to upload all glyphs again.
    ///
    /// [`can_reuse`]: Self::can_reuse
    /// [`push_widget`]: Self::push_widget
    pub fn push_reuse(&mut self, group: &mut Option<ReuseRange>, generate: impl FnOnce(&mut Self)) {
        if self.can_reuse {
            if let Some(g) = &group {
                if self.visible {
                    self.display_list.push_reuse_range(g);
                }
                return;
            }
        }
        *group = None;
        let parent_group = self.open_reuse.replace(self.display_list.start_reuse_range());

        generate(self);

        let start = self.open_reuse.take().unwrap();
        let range = self.display_list.finish_reuse_range(start);
        *group = Some(range);
        self.open_reuse = parent_group;
    }

    /// Calls `render` with [`is_visible`] set to `false`.
    ///
    /// Nodes that set the visibility to [`Hidden`] must render using this method and update using the [`FrameUpdate::hidden`] method.
    ///
    /// Note that for [`Collapsed`] the widget is automatically not rendered if [`WidgetLayout::collapse`] or other related
    /// collapse method was already called for it.
    ///
    /// [`is_visible`]: Self::is_visible
    /// [`Hidden`]: crate::widget::info::Visibility::Hidden
    /// [`Collapsed`]: crate::widget::info::Visibility::Collapsed
    /// [`WidgetLayout::collapse`]: crate::widget::info::WidgetLayout::collapse
    pub fn hide(&mut self, render: impl FnOnce(&mut Self)) {
        let parent_visible = mem::replace(&mut self.visible, false);
        render(self);
        self.visible = parent_visible;
    }

    /// Calls `render` with back face visibility set to `visible`.
    ///
    /// All visual display items pushed inside `render` will have the `visible` flag.
    pub fn with_backface_visibility(&mut self, visible: bool, render: impl FnOnce(&mut Self)) {
        if self.backface_visible != visible {
            let parent = self.backface_visible;
            self.display_list.set_backface_visibility(visible);
            render(self);
            self.display_list.set_backface_visibility(parent);
            self.backface_visible = parent;
        } else {
            render(self);
        }
    }

    /// Returns `true` if the widget stacking context is still being build.
    ///
    /// This is `true` when inside an [`push_widget`] call but `false` when inside an [`push_inner`] call.
    ///
    /// [`push_widget`]: Self::push_widget
    /// [`push_inner`]: Self::push_inner
    pub fn is_outer(&self) -> bool {
        self.widget_data.is_some()
    }

    /// Includes a widget filter and continues the render build.
    ///
    /// This is valid only when [`is_outer`].
    ///
    /// When [`push_inner`] is called a stacking context is created for the widget that includes the `filter`.
    ///
    /// [`is_outer`]: Self::is_outer
    /// [`push_inner`]: Self::push_inner
    pub fn push_inner_filter(&mut self, filter: RenderFilter, render: impl FnOnce(&mut Self)) {
        if let Some(data) = self.widget_data.as_mut() {
            let mut filter = filter;
            filter.reverse();
            data.filter.extend(filter.iter().copied());

            render(self);
        } else {
            tracing::error!("called `push_inner_filter` inside inner context of `{}`", self.widget_id);
            render(self);
        }
    }

    /// Includes a widget opacity filter and continues the render build.
    ///
    /// This is valid only when [`is_outer`].
    ///
    /// When [`push_inner`] is called a stacking context is created for the widget that includes the opacity filter.
    ///
    /// [`is_outer`]: Self::is_outer
    /// [`push_inner`]: Self::push_inner
    pub fn push_inner_opacity(&mut self, bind: FrameValue<f32>, render: impl FnOnce(&mut Self)) {
        if let Some(data) = self.widget_data.as_mut() {
            data.filter.push(FilterOp::Opacity(bind));

            render(self);
        } else {
            tracing::error!("called `push_inner_opacity` inside inner context of `{}`", self.widget_id);
            render(self);
        }
    }

    /// Include a widget backdrop filter and continue the render build.
    ///
    /// This is valid only when [`is_outer`].
    ///
    /// When [`push_inner`] is called the widget are is first filled with the backdrop filters.
    ///
    /// [`is_outer`]: Self::is_outer
    /// [`push_inner`]: Self::push_inner
    pub fn push_inner_backdrop_filter(&mut self, filter: RenderFilter, render: impl FnOnce(&mut Self)) {
        if let Some(data) = self.widget_data.as_mut() {
            let mut filter = filter;
            filter.reverse();
            data.backdrop_filter.extend(filter.iter().copied());

            render(self);
        } else {
            tracing::error!("called `push_inner_backdrop_filter` inside inner context of `{}`", self.widget_id);
            render(self);
        }
    }

    /// Sets the widget blend mode and continue the render build.
    ///
    /// This is valid only when [`is_outer`].
    ///
    /// When [`push_inner`] is called the `mode` is used to blend with the parent content.
    ///
    /// [`is_outer`]: Self::is_outer
    /// [`push_inner`]: Self::push_inner
    pub fn push_inner_blend(&mut self, mode: RenderMixBlendMode, render: impl FnOnce(&mut Self)) {
        if let Some(data) = self.widget_data.as_mut() {
            data.blend = mode;

            render(self);
        } else {
            tracing::error!("called `push_inner_blend` inside inner context of `{}`", self.widget_id);
            render(self);
        }
    }

    /// Pre-starts the scope of a widget with `offset` set for the inner reference frame. The
    /// `render` closure must call [`push_widget`] before attempting to render.
    ///
    /// Nodes that use [`WidgetLayout::with_child`] to optimize reference frames must use this method when
    /// a reference frame was not created during render.
    ///
    /// Nodes that use this must also use [`FrameUpdate::with_child`].
    ///
    /// [`push_widget`]: Self::push_widget
    /// [`WidgetLayout::with_child`]: crate::widget::info::WidgetLayout::with_child
    pub fn push_child(&mut self, offset: PxVector, render: impl FnOnce(&mut Self)) {
        if self.widget_data.is_some() {
            tracing::error!("called `push_child` outside inner context of `{}`", self.widget_id);
        }

        self.child_offset = offset;
        render(self);
        self.child_offset = PxVector::zero();
    }

    /// Include the `transform` on the widget inner reference frame.
    ///
    /// This is valid only when [`is_outer`].
    ///
    /// When [`push_inner`] is called a reference frame is created for the widget that applies the layout transform then the `transform`.
    ///
    /// [`is_outer`]: Self::is_outer
    /// [`push_inner`]: Self::push_inner
    pub fn push_inner_transform(&mut self, transform: &PxTransform, render: impl FnOnce(&mut Self)) {
        if let Some(data) = &mut self.widget_data {
            let parent_transform = data.inner_transform;
            let parent_is_set = mem::replace(&mut data.inner_is_set, true);
            data.inner_transform = data.inner_transform.then(transform);

            render(self);

            if let Some(data) = &mut self.widget_data {
                data.inner_transform = parent_transform;
                data.inner_is_set = parent_is_set;
            }
        } else {
            tracing::error!("called `push_inner_transform` inside inner context of `{}`", self.widget_id);
            render(self);
        }
    }

    /// Push the widget reference frame and stacking context then call `render` inside of it.
    ///
    /// If `layout_translation_animating` is `false` the view-process can still be updated using [`FrameUpdate::update_inner`], but
    /// a full webrender frame will be generated for each update, if is `true` webrender frame updates are used, but webrender
    /// skips some optimizations, such as auto-merging transforms. When in doubt setting this to `true` is better than `false` as
    /// a webrender frame update is faster than a full frame, and the transform related optimizations don't gain much.
    pub fn push_inner(
        &mut self,
        layout_translation_key: FrameValueKey<PxTransform>,
        layout_translation_animating: bool,
        render: impl FnOnce(&mut Self),
    ) {
        if let Some(mut data) = self.widget_data.take() {
            let parent_transform = self.transform;
            let parent_transform_style = self.transform_style;
            let parent_hit_clips = mem::take(&mut self.hit_clips);

            let wgt_info = WIDGET.info();
            let id = wgt_info.id();
            let bounds = wgt_info.bounds_info();
            let tree = wgt_info.tree();

            let inner_offset = bounds.inner_offset();
            let mut inner_transform = data.inner_transform;
            if let Some((d, mut o)) = self.perspective {
                o -= inner_offset;
                let x = o.x.0 as f32;
                let y = o.y.0 as f32;
                let p = PxTransform::translation(-x, -y)
                    .then(&PxTransform::perspective(d))
                    .then_translate(euclid::vec2(x, y));
                inner_transform = inner_transform.then(&p);
            }
            let inner_transform = inner_transform.then_translate((data.parent_child_offset + inner_offset).cast());

            self.transform = inner_transform.then(&parent_transform);

            bounds.set_inner_transform(self.transform, tree, id, self.parent_inner_bounds);

            let parent_parent_inner_bounds = mem::replace(&mut self.parent_inner_bounds, Some(bounds.inner_bounds()));

            if self.visible {
                self.transform_style = wgt_info.transform_style();

                let has_3d_ctx = matches!(self.transform_style, TransformStyle::Preserve3D);
                let has_filters = !data.filter.is_empty() || data.blend != RenderMixBlendMode::Normal;

                let mut ctx_outside_ref_frame = 0;
                let mut ctx_inside_ref_frame = 0;

                // reference frame must be just outside the stacking context, except for the
                // pre-filter context in Preserve3D roots.
                macro_rules! push_reference_frame {
                    () => {
                        self.display_list.push_reference_frame(
                            ReferenceFrameId::from_widget(self.widget_id).into(),
                            layout_translation_key.bind(inner_transform, layout_translation_animating),
                            self.transform_style.into(),
                            !data.inner_is_set,
                        );
                        if !data.backdrop_filter.is_empty() {
                            self.display_list
                                .push_backdrop_filter(PxRect::from_size(bounds.inner_size()), &data.backdrop_filter);
                        }
                    };
                }

                if has_filters {
                    // we want to apply filters in the top-to-bottom, left-to-right order they appear in
                    // the widget declaration, but the widget declaration expands to have the top property
                    // node be inside the bottom property node, so the bottom property ends up inserting
                    // a filter first, because we cannot insert filters after the child node render is called
                    // so we need to reverse the filters here. Left-to-right sequences are reversed on insert
                    // so they get reversed again here and everything ends up in order.
                    data.filter.reverse();

                    if has_3d_ctx {
                        // webrender ignores Preserve3D if there are filters, we work around the issue when possible here.

                        // push the Preserve3D, unlike CSS we prefer this over filters.

                        if matches!(
                            (self.transform_style, bounds.transform_style()),
                            (TransformStyle::Preserve3D, TransformStyle::Flat)
                        ) {
                            // is "flat root", push a nested stacking context with the filters.
                            push_reference_frame!();
                            self.display_list
                                .push_stacking_context(RenderMixBlendMode::Normal, self.transform_style, &[]);
                            self.display_list
                                .push_stacking_context(data.blend, TransformStyle::Flat, &data.filter);
                            ctx_inside_ref_frame = 2;
                        } else if wgt_info
                            .parent()
                            .map(|p| matches!(p.bounds_info().transform_style(), TransformStyle::Flat))
                            .unwrap_or(false)
                        {
                            // is "3D root", push the filters first, then the 3D root.

                            self.display_list
                                .push_stacking_context(data.blend, TransformStyle::Flat, &data.filter);
                            ctx_outside_ref_frame = 1;
                            push_reference_frame!();
                            self.display_list
                                .push_stacking_context(RenderMixBlendMode::Normal, self.transform_style, &[]);
                            ctx_inside_ref_frame = 1;
                        } else {
                            // extends 3D space, cannot splice a filters stacking context because that
                            // would disconnect the sub-tree from the parent space.
                            tracing::warn!(
                                "widget `{id}` cannot have filters because it is `Preserve3D` inside `Preserve3D`, filters & blend ignored"
                            );

                            push_reference_frame!();
                            self.display_list
                                .push_stacking_context(RenderMixBlendMode::Normal, self.transform_style, &[]);
                            ctx_inside_ref_frame = 1;
                        }
                    } else {
                        // no 3D context, push the filters context
                        push_reference_frame!();
                        self.display_list
                            .push_stacking_context(data.blend, TransformStyle::Flat, &data.filter);
                        ctx_inside_ref_frame = 1;
                    }
                } else if has_3d_ctx {
                    // just 3D context
                    push_reference_frame!();
                    self.display_list
                        .push_stacking_context(RenderMixBlendMode::Normal, self.transform_style, &[]);
                    ctx_inside_ref_frame = 1;
                } else {
                    // just flat, no filters
                    push_reference_frame!();
                }

                render(self);

                while ctx_inside_ref_frame > 0 {
                    self.display_list.pop_stacking_context();
                    ctx_inside_ref_frame -= 1;
                }

                self.display_list.pop_reference_frame();

                while ctx_outside_ref_frame > 0 {
                    self.display_list.pop_stacking_context();
                    ctx_outside_ref_frame -= 1;
                }
            } else {
                render(self);
            }

            self.transform = parent_transform;
            self.transform_style = parent_transform_style;
            self.parent_inner_bounds = parent_parent_inner_bounds;

            let hit_clips = mem::replace(&mut self.hit_clips, parent_hit_clips);
            bounds.set_hit_clips(hit_clips);

            if !self.debug_dot_overlays.is_empty() && wgt_info.parent().is_none() {
                for (offset, color) in mem::take(&mut self.debug_dot_overlays) {
                    self.push_debug_dot(offset, color);
                }
            }
        } else {
            tracing::error!("called `push_inner` more then once for `{}`", self.widget_id);
            render(self)
        }
    }

    /// Returns `true` if the widget reference frame and stacking context is pushed and now is time for rendering the widget.
    ///
    /// This is `true` when inside a [`push_inner`] call but `false` when inside a [`push_widget`] call.
    ///
    /// [`push_widget`]: Self::push_widget
    /// [`push_inner`]: Self::push_inner
    pub fn is_inner(&self) -> bool {
        self.widget_data.is_none()
    }

    /// Gets the inner-bounds hit-test shape builder.
    ///
    /// Note that all hit-test is clipped by the inner-bounds, the shapes pushed with this builder
    /// only refine the widget inner-bounds, shapes out-of-bounds are clipped.
    pub fn hit_test(&mut self) -> HitTestBuilder {
        expect_inner!(self.hit_test);

        HitTestBuilder {
            hit_clips: &mut self.hit_clips,
            is_hit_testable: self.hit_testable,
        }
    }

    /// Calls `render` with a new clip context that adds the `clip_rect`.
    ///
    /// If `clip_out` is `true` only pixels outside the rect are visible. If `hit_test` is `true` the hit-test shapes
    /// rendered inside `render` are also clipped.
    ///
    /// Note that hit-test will be generated if `hit_test` or [`auto_hit_test`] is `true`.
    ///
    /// [`auto_hit_test`]: Self::auto_hit_test
    pub fn push_clip_rect(&mut self, clip_rect: PxRect, clip_out: bool, hit_test: bool, render: impl FnOnce(&mut FrameBuilder)) {
        self.push_clips(move |c| c.push_clip_rect(clip_rect, clip_out, hit_test), render)
    }

    /// Calls `render` with a new clip context that adds the `clip_rect` with rounded `corners`.
    ///
    /// If `clip_out` is `true` only pixels outside the rounded rect are visible. If `hit_test` is `true` the hit-test shapes
    /// rendered inside `render` are also clipped.
    ///
    /// Note that hit-test will be generated if `hit_test` or [`auto_hit_test`] is `true`.
    ///
    /// [`auto_hit_test`]: Self::auto_hit_test
    pub fn push_clip_rounded_rect(
        &mut self,
        clip_rect: PxRect,
        corners: PxCornerRadius,
        clip_out: bool,
        hit_test: bool,
        render: impl FnOnce(&mut FrameBuilder),
    ) {
        self.push_clips(move |c| c.push_clip_rounded_rect(clip_rect, corners, clip_out, hit_test), render)
    }

    /// Calls `clips` to push multiple clips that define a new clip context, then calls `render` in the clip context.
    pub fn push_clips(&mut self, clips: impl FnOnce(&mut ClipBuilder), render: impl FnOnce(&mut FrameBuilder)) {
        expect_inner!(self.push_clips);

        let (mut render_count, mut hit_test_count) = {
            let mut clip_builder = ClipBuilder {
                builder: self,
                render_count: 0,
                hit_test_count: 0,
            };
            clips(&mut clip_builder);
            (clip_builder.render_count, clip_builder.hit_test_count)
        };

        render(self);

        while hit_test_count > 0 {
            hit_test_count -= 1;

            self.hit_clips.pop_clip();
        }
        while render_count > 0 {
            render_count -= 1;

            self.display_list.pop_clip();
        }
    }

    /// Push an image mask that affects all visual rendered by `render`.
    pub fn push_mask(&mut self, image: &impl Img, rect: PxRect, render: impl FnOnce(&mut Self)) {
        let mut pop = false;
        if self.visible {
            if let Some(r) = &self.renderer {
                self.display_list.push_mask(image.renderer_id(r), rect);
                pop = true;
            }
        }

        render(self);

        if pop {
            self.display_list.pop_mask();
        }
    }

    /// Calls `render` inside a new reference frame transformed by `transform`.
    ///
    /// The `is_2d_scale_translation` flag optionally marks the `transform` as only ever having a simple 2D scale or translation,
    /// allowing for webrender optimizations.
    ///
    /// If `hit_test` is `true` the hit-test shapes rendered inside `render` for the same widget are also transformed.
    ///
    /// Note that [`auto_hit_test`] overwrites `hit_test` if it is `true`.
    ///
    /// [`push_inner`]: Self::push_inner
    /// [`WidgetLayout`]: crate::widget::info::WidgetLayout
    /// [`auto_hit_test`]: Self::auto_hit_test
    /// [`Preserve3D`]: TransformStyle::Preserve3D
    pub fn push_reference_frame(
        &mut self,
        key: ReferenceFrameId,
        transform: FrameValue<PxTransform>,
        is_2d_scale_translation: bool,
        hit_test: bool,
        render: impl FnOnce(&mut Self),
    ) {
        let transform_value = transform.value();

        let prev_transform = self.transform;
        self.transform = transform_value.then(&prev_transform);

        if self.visible {
            self.display_list
                .push_reference_frame(key.into(), transform, self.transform_style, is_2d_scale_translation);
        }

        let hit_test = hit_test || self.auto_hit_test;

        if hit_test {
            self.hit_clips.push_transform(transform);
        }

        render(self);

        if self.visible {
            self.display_list.pop_reference_frame();
        }
        self.transform = prev_transform;

        if hit_test {
            self.hit_clips.pop_transform();
        }
    }

    /// Calls `render` with added `blend` and `filter` stacking context.
    ///
    /// Note that this introduces a new stacking context, you can use the [`push_inner_blend`] and [`push_inner_filter`] methods to
    /// add to the widget stacking context.
    ///
    /// [`push_inner_blend`]: Self::push_inner_blend
    /// [`push_inner_filter`]: Self::push_inner_filter
    pub fn push_filter(&mut self, blend: RenderMixBlendMode, filter: &RenderFilter, render: impl FnOnce(&mut Self)) {
        expect_inner!(self.push_filter);

        if self.visible {
            self.display_list.push_stacking_context(blend, self.transform_style, filter);

            render(self);

            self.display_list.pop_stacking_context();
        } else {
            render(self);
        }
    }

    /// Calls `render` with added opacity stacking context.
    ///
    /// Note that this introduces a new stacking context, you can use the [`push_inner_opacity`] method to
    /// add to the widget stacking context.
    ///
    /// [`push_inner_opacity`]: Self::push_inner_opacity
    pub fn push_opacity(&mut self, bind: FrameValue<f32>, render: impl FnOnce(&mut Self)) {
        expect_inner!(self.push_opacity);

        if self.visible {
            self.display_list
                .push_stacking_context(RenderMixBlendMode::Normal, self.transform_style, &[FilterOp::Opacity(bind)]);

            render(self);

            self.display_list.pop_stacking_context();
        } else {
            render(self);
        }
    }

    /// Push a standalone backdrop filter.
    ///
    /// The `filter` will apply to all pixels already rendered in `clip_rect`.
    ///
    /// Note that you can add backdrop filters to the widget using the [`push_inner_backdrop_filter`] method.
    ///
    /// [`push_inner_backdrop_filter`]: Self::push_inner_backdrop_filter
    pub fn push_backdrop_filter(&mut self, clip_rect: PxRect, filter: &RenderFilter) {
        expect_inner!(self.push_backdrop_filter);
        warn_empty!(self.push_backdrop_filter(clip_rect));

        if self.visible {
            self.display_list.push_backdrop_filter(clip_rect, filter);
        }

        if self.auto_hit_test {
            self.hit_test().push_rect(clip_rect);
        }
    }

    /// Push a border.
    pub fn push_border(&mut self, bounds: PxRect, widths: PxSideOffsets, sides: BorderSides, radius: PxCornerRadius) {
        expect_inner!(self.push_border);
        warn_empty!(self.push_border(bounds));

        if self.visible {
            self.display_list.push_border(
                bounds,
                widths,
                sides.top.into(),
                sides.right.into(),
                sides.bottom.into(),
                sides.left.into(),
                radius,
            );
        }

        if self.auto_hit_test {
            self.hit_test().push_border(bounds, widths, radius);
        }
    }

    /// Push a nine-patch border with image source.
    #[allow(clippy::too_many_arguments)]
    pub fn push_border_image(
        &mut self,
        bounds: PxRect,
        widths: PxSideOffsets,
        fill: bool,
        repeat_horizontal: RepeatMode,
        repeat_vertical: RepeatMode,
        image: &impl Img,
        rendering: ImageRendering,
    ) {
        expect_inner!(self.push_border_image);
        warn_empty!(self.push_border_image(bounds));

        if let (true, Some(r)) = (self.visible, &self.renderer) {
            let image_id = image.renderer_id(r);
            self.display_list.push_nine_patch_border(
                bounds,
                NinePatchSource::Image { image_id, rendering },
                widths,
                fill,
                repeat_horizontal,
                repeat_vertical,
            )
        }
    }

    /// Push a nine-patch border with linear gradient source.
    #[allow(clippy::too_many_arguments)]
    pub fn push_border_linear_gradient(
        &mut self,
        bounds: PxRect,
        widths: PxSideOffsets,
        fill: bool,
        repeat_horizontal: RepeatMode,
        repeat_vertical: RepeatMode,
        line: PxLine,
        stops: &[RenderGradientStop],
        extend_mode: RenderExtendMode,
    ) {
        debug_assert!(stops.len() >= 2);
        debug_assert!(stops[0].offset.abs() < 0.00001, "first color stop must be at offset 0.0");
        debug_assert!(
            (stops[stops.len() - 1].offset - 1.0).abs() < 0.00001,
            "last color stop must be at offset 1.0"
        );
        expect_inner!(self.push_border_linear_gradient);
        warn_empty!(self.push_border_linear_gradient(bounds));

        if self.visible && !stops.is_empty() {
            self.display_list.push_nine_patch_border(
                bounds,
                NinePatchSource::LinearGradient {
                    start_point: line.start.cast(),
                    end_point: line.end.cast(),
                    extend_mode,
                    stops: stops.to_vec().into_boxed_slice(),
                },
                widths,
                fill,
                repeat_horizontal,
                repeat_vertical,
            );
        }
    }

    /// Push a nine-patch border with radial gradient source.
    #[allow(clippy::too_many_arguments)]
    pub fn push_border_radial_gradient(
        &mut self,
        bounds: PxRect,
        widths: PxSideOffsets,
        fill: bool,
        repeat_horizontal: RepeatMode,
        repeat_vertical: RepeatMode,
        center: PxPoint,
        radius: PxSize,
        stops: &[RenderGradientStop],
        extend_mode: RenderExtendMode,
    ) {
        debug_assert!(stops.len() >= 2);
        debug_assert!(stops[0].offset.abs() < 0.00001, "first color stop must be at offset 0.0");
        debug_assert!(
            (stops[stops.len() - 1].offset - 1.0).abs() < 0.00001,
            "last color stop must be at offset 1.0"
        );

        expect_inner!(self.push_border_radial_gradient);
        warn_empty!(self.push_border_radial_gradient(bounds));

        if self.visible && !stops.is_empty() {
            self.display_list.push_nine_patch_border(
                bounds,
                NinePatchSource::RadialGradient {
                    center: center.cast(),
                    radius: radius.cast(),
                    start_offset: 0.0,
                    end_offset: 1.0,
                    extend_mode,
                    stops: stops.to_vec().into_boxed_slice(),
                },
                widths,
                fill,
                repeat_horizontal,
                repeat_vertical,
            );
        }
    }

    /// Push a nine-patch border with conic gradient source.
    #[allow(clippy::too_many_arguments)]
    pub fn push_border_conic_gradient(
        &mut self,
        bounds: PxRect,
        widths: PxSideOffsets,
        fill: bool,
        repeat_horizontal: RepeatMode,
        repeat_vertical: RepeatMode,
        center: PxPoint,
        angle: AngleRadian,
        stops: &[RenderGradientStop],
        extend_mode: RenderExtendMode,
    ) {
        debug_assert!(stops.len() >= 2);
        debug_assert!(stops[0].offset.abs() < 0.00001, "first color stop must be at offset 0.0");
        debug_assert!(
            (stops[stops.len() - 1].offset - 1.0).abs() < 0.00001,
            "last color stop must be at offset 1.0"
        );

        expect_inner!(self.push_border_conic_gradient);
        warn_empty!(self.push_border_conic_gradient(bounds));

        if self.visible && !stops.is_empty() {
            self.display_list.push_nine_patch_border(
                bounds,
                NinePatchSource::ConicGradient {
                    center: center.cast(),
                    angle,
                    start_offset: 0.0,
                    end_offset: 1.0,
                    extend_mode,
                    stops: stops.to_vec().into_boxed_slice(),
                },
                widths,
                fill,
                repeat_horizontal,
                repeat_vertical,
            );
        }
    }

    /// Push a text run.
    pub fn push_text(
        &mut self,
        clip_rect: PxRect,
        glyphs: &[GlyphInstance],
        font: &impl Font,
        color: FrameValue<Rgba>,
        synthesis: FontSynthesis,
        aa: FontAntiAliasing,
    ) {
        expect_inner!(self.push_text);
        warn_empty!(self.push_text(clip_rect));

        if let Some(r) = &self.renderer {
            if !glyphs.is_empty() && self.visible && !font.is_empty_fallback() {
                let font_id = font.renderer_id(r, synthesis);

                let opts = GlyphOptions {
                    aa: match aa {
                        FontAntiAliasing::Default => self.default_font_aa,
                        aa => aa,
                    },
                    synthetic_bold: synthesis.contains(FontSynthesis::BOLD),
                    synthetic_oblique: synthesis.contains(FontSynthesis::OBLIQUE),
                };
                self.display_list.push_text(clip_rect, font_id, glyphs, color, opts);
            }
        }

        if self.auto_hit_test {
            self.hit_test().push_rect(clip_rect);
        }
    }

    /// Push an image.
    pub fn push_image(
        &mut self,
        clip_rect: PxRect,
        img_size: PxSize,
        tile_size: PxSize,
        tile_spacing: PxSize,
        image: &impl Img,
        rendering: ImageRendering,
    ) {
        expect_inner!(self.push_image);
        warn_empty!(self.push_image(clip_rect));

        if let Some(r) = &self.renderer {
            if self.visible {
                let image_key = image.renderer_id(r);
                self.display_list.push_image(
                    clip_rect,
                    image_key,
                    img_size,
                    tile_size,
                    tile_spacing,
                    rendering,
                    image.alpha_type(),
                );
            }
        }

        if self.auto_hit_test {
            self.hit_test().push_rect(clip_rect);
        }
    }

    /// Push a color rectangle.
    ///
    /// The `color` can be bound and updated using [`FrameUpdate::update_color`], note that if the color binding or update
    /// is flagged as `animating` webrender frame updates are used when color updates are send, but webrender disables some
    /// caching for the entire `clip_rect` region, this can have a big performance impact in [`RenderMode::Software`] if a large
    /// part of the screen is affected, as the entire region is redraw every full frame even if the color did not actually change.
    ///
    /// [`RenderMode::Software`]: zng_view_api::window::RenderMode::Software
    pub fn push_color(&mut self, clip_rect: PxRect, color: FrameValue<Rgba>) {
        expect_inner!(self.push_color);
        warn_empty!(self.push_color(clip_rect));

        if self.visible {
            self.display_list.push_color(clip_rect, color);
        }

        if self.auto_hit_test {
            self.hit_test().push_rect(clip_rect);
        }
    }

    /// Push a repeating linear gradient rectangle.
    ///
    /// The gradient fills the `tile_size`, the tile is repeated to fill the `rect`.
    /// The `extend_mode` controls how the gradient fills the tile after the last color stop is reached.
    ///
    /// The gradient `stops` must be normalized, first stop at 0.0 and last stop at 1.0, this
    /// is asserted in debug builds.
    #[allow(clippy::too_many_arguments)]
    pub fn push_linear_gradient(
        &mut self,
        clip_rect: PxRect,
        line: PxLine,
        stops: &[RenderGradientStop],
        extend_mode: RenderExtendMode,
        tile_origin: PxPoint,
        tile_size: PxSize,
        tile_spacing: PxSize,
    ) {
        debug_assert!(stops.len() >= 2);
        debug_assert!(stops[0].offset.abs() < 0.00001, "first color stop must be at offset 0.0");
        debug_assert!(
            (stops[stops.len() - 1].offset - 1.0).abs() < 0.00001,
            "last color stop must be at offset 1.0"
        );

        expect_inner!(self.push_linear_gradient);
        warn_empty!(self.push_linear_gradient(clip_rect));

        if !stops.is_empty() && self.visible {
            self.display_list.push_linear_gradient(
                clip_rect,
                line.start.cast(),
                line.end.cast(),
                extend_mode,
                stops,
                tile_origin,
                tile_size,
                tile_spacing,
            );
        }

        if self.auto_hit_test {
            self.hit_test().push_rect(clip_rect);
        }
    }

    /// Push a repeating radial gradient rectangle.
    ///
    /// The gradient fills the `tile_size`, the tile is repeated to fill the `rect`.
    /// The `extend_mode` controls how the gradient fills the tile after the last color stop is reached.
    ///
    /// The `center` point is relative to the top-left of the tile, the `radius` is the distance between the first
    /// and last color stop in both directions and must be a non-zero positive value.
    ///
    /// The gradient `stops` must be normalized, first stop at 0.0 and last stop at 1.0, this
    /// is asserted in debug builds.
    #[allow(clippy::too_many_arguments)]
    pub fn push_radial_gradient(
        &mut self,
        clip_rect: PxRect,
        center: PxPoint,
        radius: PxSize,
        stops: &[RenderGradientStop],
        extend_mode: RenderExtendMode,
        tile_origin: PxPoint,
        tile_size: PxSize,
        tile_spacing: PxSize,
    ) {
        debug_assert!(stops.len() >= 2);
        debug_assert!(stops[0].offset.abs() < 0.00001, "first color stop must be at offset 0.0");
        debug_assert!(
            (stops[stops.len() - 1].offset - 1.0).abs() < 0.00001,
            "last color stop must be at offset 1.0"
        );

        expect_inner!(self.push_radial_gradient);
        warn_empty!(self.push_radial_gradient(clip_rect));

        if !stops.is_empty() && self.visible {
            self.display_list.push_radial_gradient(
                clip_rect,
                center.cast(),
                radius.cast(),
                0.0,
                1.0,
                extend_mode,
                stops,
                tile_origin,
                tile_size,
                tile_spacing,
            );
        }

        if self.auto_hit_test {
            self.hit_test().push_rect(clip_rect);
        }
    }

    /// Push a repeating conic gradient rectangle.
    ///
    /// The gradient fills the `tile_size`, the tile is repeated to fill the `rect`.
    /// The `extend_mode` controls how the gradient fills the tile after the last color stop is reached.
    ///
    /// The gradient `stops` must be normalized, first stop at 0.0 and last stop at 1.0, this
    /// is asserted in debug builds.
    #[allow(clippy::too_many_arguments)]
    pub fn push_conic_gradient(
        &mut self,
        clip_rect: PxRect,
        center: PxPoint,
        angle: AngleRadian,
        stops: &[RenderGradientStop],
        extend_mode: RenderExtendMode,
        tile_origin: PxPoint,
        tile_size: PxSize,
        tile_spacing: PxSize,
    ) {
        debug_assert!(stops.len() >= 2);
        debug_assert!(stops[0].offset.abs() < 0.00001, "first color stop must be at offset 0.0");
        debug_assert!(
            (stops[stops.len() - 1].offset - 1.0).abs() < 0.00001,
            "last color stop must be at offset 1.0"
        );

        expect_inner!(self.push_conic_gradient);
        warn_empty!(self.push_conic_gradient(clip_rect));

        if !stops.is_empty() && self.visible {
            self.display_list.push_conic_gradient(
                clip_rect,
                center.cast(),
                angle,
                0.0,
                1.0,
                extend_mode,
                stops,
                tile_origin,
                tile_size,
                tile_spacing,
            );
        }

        if self.auto_hit_test {
            self.hit_test().push_rect(clip_rect);
        }
    }

    /// Push a styled vertical or horizontal line.
    pub fn push_line(&mut self, clip_rect: PxRect, orientation: border::LineOrientation, color: Rgba, style: border::LineStyle) {
        expect_inner!(self.push_line);
        warn_empty!(self.push_line(clip_rect));

        if self.visible {
            match style.render_command() {
                RenderLineCommand::Line(style) => {
                    self.display_list.push_line(clip_rect, color, style, orientation);
                }
                RenderLineCommand::Border(style) => {
                    use border::LineOrientation as LO;
                    let widths = match orientation {
                        LO::Vertical => PxSideOffsets::new(Px(0), Px(0), Px(0), clip_rect.width()),
                        LO::Horizontal => PxSideOffsets::new(clip_rect.height(), Px(0), Px(0), Px(0)),
                    };
                    self.display_list.push_border(
                        clip_rect,
                        widths,
                        zng_view_api::BorderSide { color, style },
                        zng_view_api::BorderSide {
                            color: colors::BLACK.transparent(),
                            style: zng_view_api::BorderStyle::Hidden,
                        },
                        zng_view_api::BorderSide {
                            color: colors::BLACK.transparent(),
                            style: zng_view_api::BorderStyle::Hidden,
                        },
                        zng_view_api::BorderSide { color, style },
                        PxCornerRadius::zero(),
                    );
                }
            }
        }

        if self.auto_hit_test {
            self.hit_test().push_rect(clip_rect);
        }
    }

    /// Record the `offset` in the current context and [`push_debug_dot`] after render.
    ///
    /// [`push_debug_dot`]: Self::push_debug_dot
    pub fn push_debug_dot_overlay(&mut self, offset: PxPoint, color: impl Into<Rgba>) {
        if let Some(offset) = self.transform.transform_point(offset) {
            self.debug_dot_overlays.push((offset, color.into()));
        }
    }

    /// Push a `color` dot to mark the `offset`.
    ///
    /// The *dot* is a circle of the `color` highlighted by an white outline and shadow.
    pub fn push_debug_dot(&mut self, offset: PxPoint, color: impl Into<Rgba>) {
        if !self.visible {
            return;
        }
        let scale = self.scale_factor();

        let radius = PxSize::splat(Px(6)) * scale;
        let color = color.into();

        let center = radius.to_vector().to_point();
        let bounds = radius * 2.0.fct();

        let offset = offset - radius.to_vector();

        self.display_list.push_radial_gradient(
            PxRect::new(offset, bounds),
            center.cast(),
            radius.cast(),
            0.0,
            1.0,
            RenderExtendMode::Clamp,
            &[
                RenderGradientStop { offset: 0.0, color },
                RenderGradientStop { offset: 0.5, color },
                RenderGradientStop {
                    offset: 0.6,
                    color: colors::WHITE,
                },
                RenderGradientStop {
                    offset: 0.7,
                    color: colors::WHITE,
                },
                RenderGradientStop {
                    offset: 0.8,
                    color: colors::BLACK,
                },
                RenderGradientStop {
                    offset: 1.0,
                    color: colors::BLACK.transparent(),
                },
            ],
            PxPoint::zero(),
            bounds,
            PxSize::zero(),
        );
    }

    /// Push a custom display extension context with custom encoding.
    pub fn push_extension_context_raw(
        &mut self,
        extension_id: ApiExtensionId,
        payload: ApiExtensionPayload,
        render: impl FnOnce(&mut Self),
    ) {
        self.display_list.push_extension(extension_id, payload);
        render(self);
        self.display_list.pop_extension(extension_id);
    }

    /// Push a custom display extension context that wraps `render`.
    pub fn push_extension_context<T: serde::Serialize>(
        &mut self,
        extension_id: ApiExtensionId,
        payload: &T,
        render: impl FnOnce(&mut Self),
    ) {
        self.push_extension_context_raw(extension_id, ApiExtensionPayload::serialize(payload).unwrap(), render)
    }

    /// Push a custom display extension item with custom encoding.
    pub fn push_extension_item_raw(&mut self, extension_id: ApiExtensionId, payload: ApiExtensionPayload) {
        self.display_list.push_extension(extension_id, payload);
    }

    /// Push a custom display extension item.
    pub fn push_extension_item<T: serde::Serialize>(&mut self, extension_id: ApiExtensionId, payload: &T) {
        self.push_extension_item_raw(extension_id, ApiExtensionPayload::serialize(payload).unwrap())
    }

    /// Create a new display list builder that can be built in parallel and merged back onto this one using [`parallel_fold`].
    ///
    /// Note that split list must be folded before any open reference frames, stacking contexts or clips are closed in this list.
    ///
    /// [`parallel_fold`]: Self::parallel_fold
    pub fn parallel_split(&self) -> ParallelBuilder<Self> {
        if self.widget_data.is_some() && WIDGET.parent_id().is_some() {
            tracing::error!(
                "called `parallel_split` inside `{}` and before calling `push_inner`",
                self.widget_id
            );
        }

        ParallelBuilder(Some(Self {
            render_widgets: self.render_widgets.clone(),
            render_update_widgets: self.render_update_widgets.clone(),
            frame_id: self.frame_id,
            widget_id: self.widget_id,
            transform: self.transform,
            transform_style: self.transform_style,
            default_font_aa: self.default_font_aa,
            renderer: self.renderer.clone(),
            scale_factor: self.scale_factor,
            display_list: self.display_list.parallel_split(),
            hit_testable: self.hit_testable,
            visible: self.visible,
            backface_visible: self.backface_visible,
            auto_hit_test: self.auto_hit_test,
            hit_clips: self.hit_clips.parallel_split(),
            auto_hide_rect: self.auto_hide_rect,
            widget_data: None,
            child_offset: self.child_offset,
            parent_inner_bounds: self.parent_inner_bounds,
            perspective: self.perspective,
            view_process_has_frame: self.view_process_has_frame,
            can_reuse: self.can_reuse,
            open_reuse: None,
            clear_color: None,
            widget_count: 0,
            widget_count_offsets: self.widget_count_offsets.parallel_split(),
            debug_dot_overlays: vec![],
        }))
    }

    /// Collect display list from `split` into `self`.
    pub fn parallel_fold(&mut self, mut split: ParallelBuilder<Self>) {
        let split = split.take();
        if split.clear_color.is_some() {
            self.clear_color = split.clear_color;
        }
        self.hit_clips.parallel_fold(split.hit_clips);
        self.display_list.parallel_fold(split.display_list);
        self.widget_count_offsets
            .parallel_fold(split.widget_count_offsets, self.widget_count);

        self.widget_count += split.widget_count;
        self.debug_dot_overlays.extend(split.debug_dot_overlays);
    }

    /// Finalizes the build.
    pub fn finalize(self, info_tree: &WidgetInfoTree) -> BuiltFrame {
        info_tree.root().bounds_info().set_rendered(
            Some(WidgetRenderInfo {
                visible: self.visible,
                parent_perspective: self.perspective,
                seg_id: 0,
                back: 0,
                front: self.widget_count,
            }),
            info_tree,
        );

        info_tree.after_render(
            self.frame_id,
            self.scale_factor,
            Some(
                self.renderer
                    .as_ref()
                    .and_then(|r| r.generation().ok())
                    .unwrap_or(ViewProcessGen::INVALID),
            ),
            Some(self.widget_count_offsets),
        );

        let display_list = self.display_list.finalize();

        let clear_color = self.clear_color.unwrap_or_default();

        BuiltFrame { display_list, clear_color }
    }
}

/// Builder for a chain of render and hit-test clips.
///
/// The builder is available in [`FrameBuilder::push_clips`].
pub struct ClipBuilder<'a> {
    builder: &'a mut FrameBuilder,
    render_count: usize,
    hit_test_count: usize,
}
impl<'a> ClipBuilder<'a> {
    /// Pushes the `clip_rect`.
    ///
    /// If `clip_out` is `true` only pixels outside the rect are visible. If `hit_test` is `true` the hit-test shapes
    /// rendered inside `render` are also clipped.
    ///
    /// Note that hit-test will be generated if `hit_test` or [`auto_hit_test`] is `true`.
    ///
    /// [`auto_hit_test`]: FrameBuilder::auto_hit_test
    pub fn push_clip_rect(&mut self, clip_rect: PxRect, clip_out: bool, hit_test: bool) {
        if self.builder.visible {
            self.builder.display_list.push_clip_rect(clip_rect, clip_out);
            self.render_count += 1;
        }

        if hit_test || self.builder.auto_hit_test {
            self.builder.hit_clips.push_clip_rect(clip_rect.to_box2d(), clip_out);
            self.hit_test_count += 1;
        }
    }

    /// Push the `clip_rect` with rounded `corners`.
    ///
    /// If `clip_out` is `true` only pixels outside the rounded rect are visible. If `hit_test` is `true` the hit-test shapes
    /// rendered inside `render` are also clipped.
    ///
    /// Note that hit-test will be generated if `hit_test` or [`auto_hit_test`] is `true`.
    ///
    /// [`auto_hit_test`]: FrameBuilder::auto_hit_test
    pub fn push_clip_rounded_rect(&mut self, clip_rect: PxRect, corners: PxCornerRadius, clip_out: bool, hit_test: bool) {
        if self.builder.visible {
            self.builder.display_list.push_clip_rounded_rect(clip_rect, corners, clip_out);
            self.render_count += 1;
        }

        if hit_test || self.builder.auto_hit_test {
            self.builder
                .hit_clips
                .push_clip_rounded_rect(clip_rect.to_box2d(), corners, clip_out);
            self.hit_test_count += 1;
        }
    }
}

/// Builder for a chain of hit-test clips.
///
/// The build is available in [`HitTestBuilder::push_clips`].
pub struct HitTestClipBuilder<'a> {
    hit_clips: &'a mut HitTestClips,
    count: usize,
}
impl<'a> HitTestClipBuilder<'a> {
    /// Push a clip `rect`.
    ///
    /// If `clip_out` is `true` only hits outside the rect are valid.
    pub fn push_clip_rect(&mut self, rect: PxRect, clip_out: bool) {
        self.hit_clips.push_clip_rect(rect.to_box2d(), clip_out);
        self.count += 1;
    }

    /// Push a clip `rect` with rounded `corners`.
    ///
    /// If `clip_out` is `true` only hits outside the rect are valid.
    pub fn push_clip_rounded_rect(&mut self, rect: PxRect, corners: PxCornerRadius, clip_out: bool) {
        self.hit_clips.push_clip_rounded_rect(rect.to_box2d(), corners, clip_out);
        self.count += 1;
    }

    /// Push a clip ellipse.
    ///
    /// If `clip_out` is `true` only hits outside the ellipses are valid.
    pub fn push_clip_ellipse(&mut self, center: PxPoint, radii: PxSize, clip_out: bool) {
        self.hit_clips.push_clip_ellipse(center, radii, clip_out);
        self.count += 1;
    }
}

/// Builder for the hit-testable shape of the inner-bounds of a widget.
///
/// This builder is available in [`FrameBuilder::hit_test`] inside the inner-bounds of the rendering widget.
pub struct HitTestBuilder<'a> {
    hit_clips: &'a mut HitTestClips,
    is_hit_testable: bool,
}
impl<'a> HitTestBuilder<'a> {
    /// If the widget is hit-testable, if this is `false` all hit-test push methods are ignored.
    pub fn is_hit_testable(&self) -> bool {
        self.is_hit_testable
    }

    /// Push a hit-test `rect`.
    pub fn push_rect(&mut self, rect: PxRect) {
        if self.is_hit_testable && rect.size != PxSize::zero() {
            self.hit_clips.push_rect(rect.to_box2d());
        }
    }

    /// Push a hit-test `rect` with rounded `corners`.
    pub fn push_rounded_rect(&mut self, rect: PxRect, corners: PxCornerRadius) {
        if self.is_hit_testable && rect.size != PxSize::zero() {
            self.hit_clips.push_rounded_rect(rect.to_box2d(), corners);
        }
    }

    /// Push a hit-test ellipse.
    pub fn push_ellipse(&mut self, center: PxPoint, radii: PxSize) {
        if self.is_hit_testable && radii != PxSize::zero() {
            self.hit_clips.push_ellipse(center, radii);
        }
    }

    /// Push a clip `rect` that affects the `inner_hit_test`.
    pub fn push_clip_rect(&mut self, rect: PxRect, clip_out: bool, inner_hit_test: impl FnOnce(&mut Self)) {
        if !self.is_hit_testable {
            return;
        }

        self.hit_clips.push_clip_rect(rect.to_box2d(), clip_out);

        inner_hit_test(self);

        self.hit_clips.pop_clip();
    }

    /// Push a clip `rect` with rounded `corners` that affects the `inner_hit_test`.
    pub fn push_clip_rounded_rect(
        &mut self,
        rect: PxRect,
        corners: PxCornerRadius,
        clip_out: bool,
        inner_hit_test: impl FnOnce(&mut Self),
    ) {
        self.push_clips(move |c| c.push_clip_rounded_rect(rect, corners, clip_out), inner_hit_test);
    }

    /// Push a clip ellipse that affects the `inner_hit_test`.
    pub fn push_clip_ellipse(&mut self, center: PxPoint, radii: PxSize, clip_out: bool, inner_hit_test: impl FnOnce(&mut Self)) {
        self.push_clips(move |c| c.push_clip_ellipse(center, radii, clip_out), inner_hit_test);
    }

    /// Push clips that affect the `inner_hit_test`.
    pub fn push_clips(&mut self, clips: impl FnOnce(&mut HitTestClipBuilder), inner_hit_test: impl FnOnce(&mut Self)) {
        if !self.is_hit_testable {
            return;
        }

        let mut count = {
            let mut builder = HitTestClipBuilder {
                hit_clips: &mut *self.hit_clips,
                count: 0,
            };
            clips(&mut builder);
            builder.count
        };

        inner_hit_test(self);

        while count > 0 {
            count -= 1;
            self.hit_clips.pop_clip();
        }
    }

    /// Pushes a transform that affects the `inner_hit_test`.
    pub fn push_transform(&mut self, transform: PxTransform, inner_hit_test: impl FnOnce(&mut Self)) {
        if !self.is_hit_testable {
            return;
        }

        self.hit_clips.push_transform(FrameValue::Value(transform));

        inner_hit_test(self);

        self.hit_clips.pop_transform();
    }

    /// Pushes a composite hit-test that defines a border.
    pub fn push_border(&mut self, bounds: PxRect, widths: PxSideOffsets, corners: PxCornerRadius) {
        if !self.is_hit_testable {
            return;
        }

        let bounds = bounds.to_box2d();
        let mut inner_bounds = bounds;
        inner_bounds.min.x += widths.left;
        inner_bounds.min.y += widths.top;
        inner_bounds.max.x -= widths.right;
        inner_bounds.max.y -= widths.bottom;

        if inner_bounds.is_negative() {
            self.hit_clips.push_rounded_rect(bounds, corners);
        } else if corners == PxCornerRadius::zero() {
            self.hit_clips.push_clip_rect(inner_bounds, true);
            self.hit_clips.push_rect(bounds);
            self.hit_clips.pop_clip();
        } else {
            let inner_radii = corners.deflate(widths);

            self.hit_clips.push_clip_rounded_rect(inner_bounds, inner_radii, true);
            self.hit_clips.push_rounded_rect(bounds, corners);
            self.hit_clips.pop_clip();
        }
    }
}

/// Output of a [`FrameBuilder`].
pub struct BuiltFrame {
    /// Built display list.
    pub display_list: DisplayList,
    /// Clear color selected for the frame.
    pub clear_color: Rgba,
}

enum RenderLineCommand {
    Line(zng_view_api::LineStyle),
    Border(zng_view_api::BorderStyle),
}
impl border::LineStyle {
    fn render_command(self) -> RenderLineCommand {
        use border::LineStyle as LS;
        use RenderLineCommand::*;
        match self {
            LS::Solid => Line(zng_view_api::LineStyle::Solid),
            LS::Double => Border(zng_view_api::BorderStyle::Double),
            LS::Dotted => Line(zng_view_api::LineStyle::Dotted),
            LS::Dashed => Line(zng_view_api::LineStyle::Dashed),
            LS::Groove => Border(zng_view_api::BorderStyle::Groove),
            LS::Ridge => Border(zng_view_api::BorderStyle::Ridge),
            LS::Wavy(thickness) => Line(zng_view_api::LineStyle::Wavy(thickness)),
            LS::Hidden => Border(zng_view_api::BorderStyle::Hidden),
        }
    }
}

/// A frame quick update.
///
/// A frame update causes a frame render without needing to fully rebuild the display list. It
/// is a more performant but also more limited way of generating a frame.
///
/// Any [`FrameValueKey`] used in the creation of the frame can be used for updating the frame.
pub struct FrameUpdate {
    render_update_widgets: Arc<RenderUpdates>,

    transforms: Vec<FrameValueUpdate<PxTransform>>,
    floats: Vec<FrameValueUpdate<f32>>,
    colors: Vec<FrameValueUpdate<Rgba>>,

    extensions: Vec<(ApiExtensionId, ApiExtensionPayload)>,

    current_clear_color: Rgba,
    clear_color: Option<Rgba>,
    frame_id: FrameId,

    widget_id: WidgetId,
    transform: PxTransform,
    parent_child_offset: PxVector,
    perspective: Option<(f32, PxPoint)>,
    inner_transform: Option<PxTransform>,
    child_offset: PxVector,
    can_reuse_widget: bool,
    widget_bounds: WidgetBoundsInfo,
    parent_inner_bounds: Option<PxRect>,

    auto_hit_test: bool,
    visible: bool,
}
impl FrameUpdate {
    /// New frame update builder.
    ///
    /// * `render_update_widgets` - External update requests.
    /// * `frame_id` - Id of the new frame.
    /// * `root_id` - Id of the window root widget.
    /// * `renderer` - Reference to the renderer that will update.
    /// * `clear_color` - The current clear color.
    pub fn new(
        render_update_widgets: Arc<RenderUpdates>,
        frame_id: FrameId,
        root_id: WidgetId,
        root_bounds: WidgetBoundsInfo,
        renderer: Option<&ViewRenderer>,
        clear_color: Rgba,
    ) -> Self {
        let _ = renderer;
        FrameUpdate {
            render_update_widgets,
            widget_id: root_id,
            widget_bounds: root_bounds,
            transforms: vec![],
            floats: vec![],
            colors: vec![],
            extensions: vec![],
            clear_color: None,
            frame_id,
            current_clear_color: clear_color,

            transform: PxTransform::identity(),
            perspective: None,
            parent_child_offset: PxVector::zero(),
            inner_transform: Some(PxTransform::identity()),
            child_offset: PxVector::zero(),
            can_reuse_widget: true,

            auto_hit_test: false,
            parent_inner_bounds: None,
            visible: true,
        }
    }

    /// Id of the new frame.
    pub fn frame_id(&self) -> FrameId {
        self.frame_id
    }

    /// Returns `true` if the widget inner transform update is still being build.
    ///
    /// This is `true` when inside an [`update_widget`] call but `false` when inside an [`update_inner`] call.
    ///
    /// [`update_widget`]: Self::update_widget
    /// [`update_inner`]: Self::update_inner
    pub fn is_outer(&self) -> bool {
        self.inner_transform.is_some()
    }

    /// Current transform.
    pub fn transform(&self) -> &PxTransform {
        &self.transform
    }

    /// Change the color used to clear the pixel buffer when redrawing the frame.
    pub fn set_clear_color(&mut self, color: Rgba) {
        if self.visible {
            self.clear_color = Some(color);
        }
    }

    /// Returns `true` if all transform updates are also applied to hit-test transforms.
    pub fn auto_hit_test(&self) -> bool {
        self.auto_hit_test
    }
    /// Runs `render_update` with [`auto_hit_test`] set to a value for the duration of the `render` call.
    ///
    /// [`auto_hit_test`]: Self::auto_hit_test
    pub fn with_auto_hit_test(&mut self, auto_hit_test: bool, render_update: impl FnOnce(&mut Self)) {
        let prev = mem::replace(&mut self.auto_hit_test, auto_hit_test);
        render_update(self);
        self.auto_hit_test = prev;
    }

    /// Returns `true` if view updates are actually collected, if `false` only transforms and hit-test are updated.
    pub fn is_visible(&self) -> bool {
        self.visible
    }

    /// Calls `update` with [`is_visible`] set to `false`.
    ///
    /// Nodes that set the visibility to [`Hidden`] must render using the [`FrameBuilder::hide`] method and update using this method.
    ///
    /// [`is_visible`]: Self::is_visible
    /// [`Hidden`]: crate::widget::info::Visibility::Hidden
    pub fn hidden(&mut self, update: impl FnOnce(&mut Self)) {
        let parent_visible = mem::replace(&mut self.visible, false);
        update(self);
        self.visible = parent_visible;
    }

    /// Update a transform value that does not potentially affect widget bounds.
    ///
    /// Use [`with_transform`] to update transforms that affect widget bounds.
    ///
    /// If `hit_test` is `true` the hit-test transform is also updated.
    ///
    /// [`with_transform`]: Self::with_transform
    pub fn update_transform(&mut self, new_value: FrameValueUpdate<PxTransform>, hit_test: bool) {
        if self.visible {
            self.transforms.push(new_value);
        }

        if hit_test || self.auto_hit_test {
            self.widget_bounds.update_hit_test_transform(new_value);
        }
    }

    /// Update a transform value, if there is one.
    pub fn update_transform_opt(&mut self, new_value: Option<FrameValueUpdate<PxTransform>>, hit_test: bool) {
        if let Some(value) = new_value {
            self.update_transform(value, hit_test)
        }
    }

    /// Update a transform that potentially affects widget bounds.
    ///
    /// The [`transform`] is updated to include this space for the call to the `render_update` closure. The closure
    /// must call render update on child nodes.
    ///
    /// If `hit_test` is `true` the hit-test transform is also updated.
    ///
    /// [`transform`]: Self::transform
    pub fn with_transform(&mut self, new_value: FrameValueUpdate<PxTransform>, hit_test: bool, render_update: impl FnOnce(&mut Self)) {
        self.with_transform_value(&new_value.value, render_update);
        self.update_transform(new_value, hit_test);
    }

    /// Update a transform that potentially affects widget bounds, if there is one.
    ///
    /// The `render_update` is always called.
    pub fn with_transform_opt(
        &mut self,
        new_value: Option<FrameValueUpdate<PxTransform>>,
        hit_test: bool,
        render_update: impl FnOnce(&mut Self),
    ) {
        match new_value {
            Some(value) => self.with_transform(value, hit_test, render_update),
            None => render_update(self),
        }
    }

    /// Calls `render_update` with an `offset` that affects the first inner child inner bounds.
    ///
    /// Nodes that used [`FrameBuilder::push_child`] during render must use this method to update the value.
    pub fn with_child(&mut self, offset: PxVector, render_update: impl FnOnce(&mut Self)) {
        self.child_offset = offset;
        render_update(self);
        self.child_offset = PxVector::zero();
    }

    /// Calls `render_update` while the [`transform`] is updated to include the `value` space.
    ///
    /// This is useful for cases where the inner transforms are affected by a `value` that is only rendered, never updated.
    ///
    /// [`transform`]: Self::transform
    pub fn with_transform_value(&mut self, value: &PxTransform, render_update: impl FnOnce(&mut Self)) {
        let parent_transform = self.transform;
        self.transform = value.then(&parent_transform);

        render_update(self);
        self.transform = parent_transform;
    }

    /// Update the transform applied after the inner bounds translate.
    ///
    /// This is only valid if [`is_outer`].
    ///
    /// [`is_outer`]: Self::is_outer
    pub fn with_inner_transform(&mut self, transform: &PxTransform, render_update: impl FnOnce(&mut Self)) {
        if let Some(inner_transform) = &mut self.inner_transform {
            let parent = *inner_transform;
            *inner_transform = inner_transform.then(transform);

            render_update(self);

            if let Some(inner_transform) = &mut self.inner_transform {
                *inner_transform = parent;
            }
        } else {
            tracing::error!("called `with_inner_transform` inside inner context of `{}`", self.widget_id);
            render_update(self);
        }
    }

    /// If widget update can be *skipped* by setting reuse in [`update_widget`].
    ///
    /// [`update_widget`]: Self::update_widget
    pub fn can_reuse_widget(&self) -> bool {
        self.can_reuse_widget
    }

    /// Calls `render_update` with [`can_reuse_widget`] set to `false`.
    ///
    /// [`can_reuse_widget`]: Self::can_reuse_widget
    pub fn with_no_reuse(&mut self, render_update: impl FnOnce(&mut Self)) {
        let prev_can_reuse = self.can_reuse_widget;
        self.can_reuse_widget = false;
        render_update(self);
        self.can_reuse_widget = prev_can_reuse;
    }

    /// Update the widget's outer transform.
    ///
    /// If render-update was not requested for the widget and [`can_reuse_widget`] only update outer/inner transforms of descendants.
    /// If the widget is reused the `render_update` is not called.
    ///
    /// [`can_reuse_widget`]: Self::can_reuse_widget
    pub fn update_widget(&mut self, render_update: impl FnOnce(&mut Self)) {
        let wgt_info = WIDGET.info();
        let id = wgt_info.id();

        #[cfg(debug_assertions)]
        if self.inner_transform.is_some() && wgt_info.parent().is_some() {
            tracing::error!(
                "called `update_widget` for `{}` without calling `update_inner` for the parent `{}`",
                WIDGET.trace_id(),
                self.widget_id
            );
        }

        let bounds = wgt_info.bounds_info();
        if bounds.is_collapsed() {
            let _ = WIDGET.take_update(UpdateFlags::LAYOUT | UpdateFlags::RENDER | UpdateFlags::RENDER_UPDATE);
            return;
        } else {
            #[cfg(debug_assertions)]
            if WIDGET.pending_update().contains(UpdateFlags::LAYOUT) {
                tracing::error!("called `update_widget` for `{}` with pending layout", WIDGET.trace_id());
            }
        }

        let tree = wgt_info.tree();

        let parent_can_reuse = self.can_reuse_widget;
        let parent_perspective = mem::replace(&mut self.perspective, wgt_info.perspective());
        let parent_bounds = mem::replace(&mut self.widget_bounds, bounds.clone());

        if let Some((_, o)) = &mut self.perspective {
            *o -= self.child_offset;
        }

        let render_info = bounds.render_info();
        if let Some(i) = &render_info {
            if i.parent_perspective != self.perspective {
                self.can_reuse_widget = false;
            }
        }

        let outer_transform = PxTransform::from(self.child_offset).then(&self.transform);

        if !WIDGET.take_update(UpdateFlags::RENDER_UPDATE)
            && self.can_reuse_widget
            && !self.render_update_widgets.delivery_list().enter_widget(id)
            && bounds.parent_child_offset() == self.child_offset
        {
            let _span = tracing::trace_span!("reuse-descendants", id=?self.widget_id).entered();

            let prev_outer = bounds.outer_transform();
            if prev_outer != outer_transform {
                if let Some(undo_prev) = prev_outer.inverse() {
                    let patch = undo_prev.then(&outer_transform);

                    let update = |info: WidgetInfo| {
                        let bounds = info.bounds_info();
                        bounds.set_outer_transform(bounds.outer_transform().then(&patch), tree);
                        bounds.set_inner_transform(
                            bounds.inner_transform().then(&patch),
                            tree,
                            info.id(),
                            info.parent().map(|p| p.inner_bounds()),
                        );
                    };
                    let targets = tree.get(id).unwrap().self_and_descendants();
                    if PARALLEL_VAR.get().contains(Parallel::RENDER) {
                        targets.par_bridge().for_each(update);
                    } else {
                        targets.for_each(update);
                    }

                    return; // can reuse and patched.
                }
            } else {
                return; // can reuse and no change.
            }

            // actually cannot reuse because cannot undo prev-transform.
            self.can_reuse_widget = false;
        }

        bounds.set_parent_child_offset(self.child_offset);
        bounds.set_outer_transform(outer_transform, tree);
        self.parent_child_offset = mem::take(&mut self.child_offset);
        self.inner_transform = Some(PxTransform::identity());
        let parent_id = self.widget_id;
        self.widget_id = id;

        render_update(self);

        if let Some(mut i) = render_info {
            i.parent_perspective = self.perspective;
            bounds.set_rendered(Some(i), tree);
        }
        self.parent_child_offset = PxVector::zero();
        self.inner_transform = None;
        self.widget_id = parent_id;
        self.can_reuse_widget = parent_can_reuse;
        self.perspective = parent_perspective;
        self.widget_bounds = parent_bounds;
    }

    /// Update the info transforms of the widget and descendants.
    ///
    /// Widgets that did not request render-update can use this method to update only the outer and inner transforms
    /// of itself and descendants as those values are global and the parent widget may have changed.
    pub fn reuse_widget(&mut self) {
        if self.inner_transform.is_some() {
            tracing::error!(
                "called `reuse_widget` for `{}` without calling `update_inner` for the parent `{}`",
                WIDGET.trace_id(),
                self.widget_id
            );
        }
    }

    /// Update the widget's inner transform.
    ///
    /// The `layout_translation_animating` affects some webrender caches, see [`FrameBuilder::push_inner`] for details.
    pub fn update_inner(
        &mut self,
        layout_translation_key: FrameValueKey<PxTransform>,
        layout_translation_animating: bool,
        render_update: impl FnOnce(&mut Self),
    ) {
        let id = WIDGET.id();
        if let Some(mut inner_transform) = self.inner_transform.take() {
            let bounds = WIDGET.bounds();
            let tree = WINDOW.info();

            let inner_offset = bounds.inner_offset();
            if let Some((p, mut o)) = self.perspective {
                o -= inner_offset;
                let x = o.x.0 as f32;
                let y = o.y.0 as f32;
                let p = PxTransform::translation(-x, -y)
                    .then(&PxTransform::perspective(p))
                    .then_translate(euclid::vec2(x, y));
                inner_transform = inner_transform.then(&p);
            }
            let inner_transform = inner_transform.then_translate((self.parent_child_offset + inner_offset).cast());
            self.update_transform(layout_translation_key.update(inner_transform, layout_translation_animating), false);
            let parent_transform = self.transform;

            self.transform = inner_transform.then(&parent_transform);

            bounds.set_inner_transform(self.transform, &tree, id, self.parent_inner_bounds);
            let parent_inner_bounds = mem::replace(&mut self.parent_inner_bounds, Some(bounds.inner_bounds()));

            render_update(self);

            self.transform = parent_transform;
            self.parent_inner_bounds = parent_inner_bounds;
        } else {
            tracing::error!("called `update_inner` more then once for `{}`", id);
            render_update(self)
        }
    }

    /// Update a float value.
    pub fn update_f32(&mut self, new_value: FrameValueUpdate<f32>) {
        if self.visible {
            self.floats.push(new_value);
        }
    }

    /// Update a float value, if there is one.
    pub fn update_f32_opt(&mut self, new_value: Option<FrameValueUpdate<f32>>) {
        if let Some(value) = new_value {
            self.update_f32(value)
        }
    }

    /// Update a color value.
    ///
    /// See [`FrameBuilder::push_color`] for details.
    pub fn update_color(&mut self, new_value: FrameValueUpdate<Rgba>) {
        if self.visible {
            self.colors.push(new_value)
        }
    }

    /// Update a color value, if there is one.
    pub fn update_color_opt(&mut self, new_value: Option<FrameValueUpdate<Rgba>>) {
        if let Some(value) = new_value {
            self.update_color(value)
        }
    }

    /// Update a custom extension value with custom encoding.
    pub fn update_extension_raw(&mut self, extension_id: ApiExtensionId, extension_payload: ApiExtensionPayload) {
        self.extensions.push((extension_id, extension_payload))
    }

    /// Update a custom extension value.
    pub fn update_extension<T: serde::Serialize>(&mut self, extension_id: ApiExtensionId, payload: &T) {
        self.update_extension_raw(extension_id, ApiExtensionPayload::serialize(payload).unwrap())
    }

    /// Create an update builder that can be send to a parallel task and must be folded back into this builder.
    ///
    /// This should be called just before the call to [`update_widget`], an error is traced if called inside a widget outer bounds.
    ///
    /// [`update_widget`]: Self::update_widget
    pub fn parallel_split(&self) -> ParallelBuilder<Self> {
        if self.inner_transform.is_some() && WIDGET.parent_id().is_some() {
            tracing::error!(
                "called `parallel_split` inside `{}` and before calling `update_inner`",
                self.widget_id
            );
        }

        ParallelBuilder(Some(Self {
            render_update_widgets: self.render_update_widgets.clone(),
            current_clear_color: self.current_clear_color,
            frame_id: self.frame_id,

            transforms: vec![],
            floats: vec![],
            colors: vec![],
            extensions: vec![],
            clear_color: None,

            widget_id: self.widget_id,
            transform: self.transform,
            perspective: self.perspective,
            parent_child_offset: self.parent_child_offset,
            inner_transform: self.inner_transform,
            child_offset: self.child_offset,
            can_reuse_widget: self.can_reuse_widget,
            widget_bounds: self.widget_bounds.clone(),
            parent_inner_bounds: self.parent_inner_bounds,
            auto_hit_test: self.auto_hit_test,
            visible: self.visible,
        }))
    }

    /// Collect updates from `split` into `self`.
    pub fn parallel_fold(&mut self, mut split: ParallelBuilder<Self>) {
        let mut split = split.take();

        debug_assert_eq!(self.frame_id, split.frame_id);
        debug_assert_eq!(self.widget_id, split.widget_id);

        fn take_or_append<T>(t: &mut Vec<T>, s: &mut Vec<T>) {
            if t.is_empty() {
                *t = mem::take(s);
            } else {
                t.append(s)
            }
        }

        take_or_append(&mut self.transforms, &mut split.transforms);
        take_or_append(&mut self.floats, &mut split.floats);
        take_or_append(&mut self.colors, &mut split.colors);
        take_or_append(&mut self.extensions, &mut split.extensions);

        if let Some(c) = self.clear_color.take() {
            self.clear_color = Some(c);
        }
    }

    /// Finalize the update.
    ///
    /// Returns the property updates and the new clear color if any was set.
    pub fn finalize(mut self, info_tree: &WidgetInfoTree) -> BuiltFrameUpdate {
        info_tree.after_render_update(self.frame_id);

        if self.clear_color == Some(self.current_clear_color) {
            self.clear_color = None;
        }

        BuiltFrameUpdate {
            clear_color: self.clear_color,
            transforms: self.transforms,
            floats: self.floats,
            colors: self.colors,
            extensions: self.extensions,
        }
    }
}

/// Output of a [`FrameBuilder`].
pub struct BuiltFrameUpdate {
    /// Bound transforms update.
    pub transforms: Vec<FrameValueUpdate<PxTransform>>,
    /// Bound floats update.
    pub floats: Vec<FrameValueUpdate<f32>>,
    /// Bound colors update.
    pub colors: Vec<FrameValueUpdate<Rgba>>,
    /// New clear color.
    pub clear_color: Option<Rgba>,
    /// Renderer extension updates.
    pub extensions: Vec<(ApiExtensionId, ApiExtensionPayload)>,
}

unique_id_32! {
    #[derive(Debug)]
    struct FrameBindingKeyId;
}
impl_unique_id_bytemuck!(FrameBindingKeyId);

unique_id_32! {
    /// Unique ID of a reference frame.
    #[derive(Debug)]
    pub struct SpatialFrameId;
}
impl_unique_id_bytemuck!(SpatialFrameId);

#[derive(Clone, Copy, PartialEq, Eq)]
enum ReferenceFrameIdInner {
    Unique(SpatialFrameId),
    UniqueIndex(SpatialFrameId, u32),
    Widget(WidgetId),
    WidgetIndex(WidgetId, u32),
    FrameValue(FrameValueKey<PxTransform>),
    FrameValueIndex(FrameValueKey<PxTransform>, u32),
}
impl ReferenceFrameIdInner {
    const UNIQUE: u64 = 1 << 63;
    const WIDGET: u64 = 1 << 62;
    const FRAME_VALUE: u64 = 1 << 61;
}
impl From<ReferenceFrameIdInner> for RenderReferenceFrameId {
    fn from(value: ReferenceFrameIdInner) -> Self {
        match value {
            ReferenceFrameIdInner::UniqueIndex(id, index) => {
                RenderReferenceFrameId(id.get() as u64, index as u64 | ReferenceFrameIdInner::UNIQUE)
            }
            ReferenceFrameIdInner::WidgetIndex(id, index) => RenderReferenceFrameId(id.get(), index as u64 | ReferenceFrameIdInner::WIDGET),
            ReferenceFrameIdInner::FrameValue(key) => {
                RenderReferenceFrameId(((key.id.get() as u64) << 32) | u32::MAX as u64, ReferenceFrameIdInner::FRAME_VALUE)
            }
            ReferenceFrameIdInner::FrameValueIndex(key, index) => {
                RenderReferenceFrameId(((key.id.get() as u64) << 32) | index as u64, ReferenceFrameIdInner::FRAME_VALUE)
            }
            ReferenceFrameIdInner::Unique(id) => {
                RenderReferenceFrameId(id.get() as u64, (u32::MAX as u64 + 1) | ReferenceFrameIdInner::UNIQUE)
            }
            ReferenceFrameIdInner::Widget(id) => RenderReferenceFrameId(id.get(), (u32::MAX as u64 + 1) | ReferenceFrameIdInner::WIDGET),
        }
    }
}

/// Represents an unique key for a spatial reference frame that is recreated in multiple frames.
///
/// The key can be generated from [`WidgetId`], [`SpatialFrameId`] or [`FrameValueKey<PxTransform>`] all guaranteed
/// to be unique even if the inner value of IDs is the same.
///
/// [`FrameValueKey<PxTransform>`]: FrameValueKey
#[derive(Clone, Copy, PartialEq, Eq)]
pub struct ReferenceFrameId(ReferenceFrameIdInner);
impl ReferenceFrameId {
    /// Key used for the widget inner transform.
    ///
    /// See [`FrameBuilder::push_inner`].
    fn from_widget(widget_id: WidgetId) -> Self {
        Self(ReferenceFrameIdInner::Widget(widget_id))
    }

    /// Key from [`WidgetId`] and [`u32`] index.
    ///
    /// This can be used in nodes that know that they are the only one rendering children nodes.
    pub fn from_widget_child(parent_id: WidgetId, child_index: u32) -> Self {
        Self(ReferenceFrameIdInner::WidgetIndex(parent_id, child_index))
    }

    /// Key from [`SpatialFrameId`].
    pub fn from_unique(id: SpatialFrameId) -> Self {
        Self(ReferenceFrameIdInner::Unique(id))
    }

    /// Key from [`SpatialFrameId`] and [`u32`] index.
    pub fn from_unique_child(id: SpatialFrameId, child_index: u32) -> Self {
        Self(ReferenceFrameIdInner::UniqueIndex(id, child_index))
    }

    /// Key from a [`FrameValueKey<PxTransform>`].
    pub fn from_frame_value(frame_value_key: FrameValueKey<PxTransform>) -> Self {
        Self(ReferenceFrameIdInner::FrameValue(frame_value_key))
    }

    /// Key from a [`FrameValueKey<PxTransform>`] and [`u32`] index.
    pub fn from_frame_value_child(frame_value_key: FrameValueKey<PxTransform>, child_index: u32) -> Self {
        Self(ReferenceFrameIdInner::FrameValueIndex(frame_value_key, child_index))
    }
}
impl From<ReferenceFrameId> for RenderReferenceFrameId {
    fn from(value: ReferenceFrameId) -> Self {
        value.0.into()
    }
}
impl From<FrameValueKey<PxTransform>> for ReferenceFrameId {
    fn from(value: FrameValueKey<PxTransform>) -> Self {
        Self::from_frame_value(value)
    }
}
impl From<SpatialFrameId> for ReferenceFrameId {
    fn from(id: SpatialFrameId) -> Self {
        Self::from_unique(id)
    }
}
impl From<(SpatialFrameId, u32)> for ReferenceFrameId {
    fn from((id, index): (SpatialFrameId, u32)) -> Self {
        Self::from_unique_child(id, index)
    }
}
impl From<(WidgetId, u32)> for ReferenceFrameId {
    fn from((id, index): (WidgetId, u32)) -> Self {
        Self::from_widget_child(id, index)
    }
}
impl From<(FrameValueKey<PxTransform>, u32)> for ReferenceFrameId {
    fn from((key, index): (FrameValueKey<PxTransform>, u32)) -> Self {
        Self::from_frame_value_child(key, index)
    }
}

/// Unique key of an updatable value in the view-process frame.
#[derive(Debug)]
pub struct FrameValueKey<T> {
    id: FrameBindingKeyId,
    _type: PhantomData<T>,
}
impl<T> PartialEq for FrameValueKey<T> {
    fn eq(&self, other: &Self) -> bool {
        self.id == other.id
    }
}
impl<T> Eq for FrameValueKey<T> {}
impl<T> Clone for FrameValueKey<T> {
    fn clone(&self) -> Self {
        *self
    }
}
impl<T> Copy for FrameValueKey<T> {}
impl<T> FrameValueKey<T> {
    /// Generates a new unique ID.
    pub fn new_unique() -> Self {
        FrameValueKey {
            id: FrameBindingKeyId::new_unique(),
            _type: PhantomData,
        }
    }

    /// To view key.
    pub fn to_wr(self) -> zng_view_api::display_list::FrameValueId {
        Self::to_wr_child(self, u32::MAX)
    }

    /// To view key with an extra `index` modifier.
    pub fn to_wr_child(self, child_index: u32) -> zng_view_api::display_list::FrameValueId {
        zng_view_api::display_list::FrameValueId::from_raw(((self.id.get() as u64) << 32) | child_index as u64)
    }

    /// Create a binding with this key.
    ///
    /// The `animating` flag controls if the binding will propagate to webrender, if `true`
    /// webrender frame updates are generated for
    pub fn bind(self, value: T, animating: bool) -> FrameValue<T> {
        self.bind_child(u32::MAX, value, animating)
    }

    /// Like [`bind`] but the key is modified to include the `child_index`.
    ///
    /// [`bind`]: Self::bind
    pub fn bind_child(self, child_index: u32, value: T, animating: bool) -> FrameValue<T> {
        FrameValue::Bind {
            id: self.to_wr_child(child_index),
            value,
            animating,
        }
    }

    /// Create a value update with this key.
    pub fn update(self, value: T, animating: bool) -> FrameValueUpdate<T> {
        self.update_child(u32::MAX, value, animating)
    }

    /// Like [`update`] but the key is modified to include the `child_index`.
    ///
    /// [`update`]: Self::update
    pub fn update_child(self, child_index: u32, value: T, animating: bool) -> FrameValueUpdate<T> {
        FrameValueUpdate {
            id: self.to_wr_child(child_index),
            value,
            animating,
        }
    }

    /// Create a binding with this key and `var`.
    ///
    /// The `map` must produce a copy or clone of the frame value.
    pub fn bind_var<VT: VarValue>(self, var: &impl Var<VT>, map: impl FnOnce(&VT) -> T) -> FrameValue<T> {
        self.bind_var_child(u32::MAX, var, map)
    }

    /// Like [`bind_var`] but the key is modified to include the `child_index`.
    ///
    /// [`bind_var`]: Self::bind_var
    pub fn bind_var_child<VT: VarValue>(self, child_index: u32, var: &impl Var<VT>, map: impl FnOnce(&VT) -> T) -> FrameValue<T> {
        if var.capabilities().contains(VarCapability::NEW) {
            FrameValue::Bind {
                id: self.to_wr_child(child_index),
                value: var.with(map),
                animating: var.is_animating(),
            }
        } else {
            FrameValue::Value(var.with(map))
        }
    }

    /// Create a binding with this key, `var` and already mapped `value`.
    pub fn bind_var_mapped<VT: VarValue>(&self, var: &impl Var<VT>, value: T) -> FrameValue<T> {
        self.bind_var_mapped_child(u32::MAX, var, value)
    }

    /// Like [`bind_var_mapped`] but the key is modified to include the `child_index`.
    ///
    /// [`bind_var_mapped`]: Self::bind_var_mapped
    pub fn bind_var_mapped_child<VT: VarValue>(&self, child_index: u32, var: &impl Var<VT>, value: T) -> FrameValue<T> {
        if var.capabilities().contains(VarCapability::NEW) {
            FrameValue::Bind {
                id: self.to_wr_child(child_index),
                value,
                animating: var.is_animating(),
            }
        } else {
            FrameValue::Value(value)
        }
    }

    /// Create a value update with this key and `var`.
    pub fn update_var<VT: VarValue>(self, var: &impl Var<VT>, map: impl FnOnce(&VT) -> T) -> Option<FrameValueUpdate<T>> {
        self.update_var_child(u32::MAX, var, map)
    }

    /// Like [`update_var`] but the key is modified to include the `child_index`.
    ///
    /// [`update_var`]: Self::update_var
    pub fn update_var_child<VT: VarValue>(
        self,
        child_index: u32,
        var: &impl Var<VT>,
        map: impl FnOnce(&VT) -> T,
    ) -> Option<FrameValueUpdate<T>> {
        if var.capabilities().contains(VarCapability::NEW) {
            Some(FrameValueUpdate {
                id: self.to_wr_child(child_index),
                value: var.with(map),
                animating: var.is_animating(),
            })
        } else {
            None
        }
    }

    /// Create a value update with this key, `var` and already mapped `value`.
    pub fn update_var_mapped<VT: VarValue>(self, var: &impl Var<VT>, value: T) -> Option<FrameValueUpdate<T>> {
        self.update_var_mapped_child(u32::MAX, var, value)
    }

    /// Like [`update_var_mapped`] but the key is modified to include the `child_index`.
    ///
    /// [`update_var_mapped`]: Self::update_var_mapped
    pub fn update_var_mapped_child<VT: VarValue>(self, child_index: u32, var: &impl Var<VT>, value: T) -> Option<FrameValueUpdate<T>> {
        if var.capabilities().contains(VarCapability::NEW) {
            Some(FrameValueUpdate {
                id: self.to_wr_child(child_index),
                value,
                animating: var.is_animating(),
            })
        } else {
            None
        }
    }
}

bitflags::bitflags! {
    /// Configure if a synthetic font is generated for fonts that do not implement **bold** or *oblique* variants.
    #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
    #[serde(transparent)]
    pub struct FontSynthesis: u8 {
        /// No synthetic font generated, if font resolution does not find a variant the matches the requested style and weight
        /// the request is ignored and the normal font is returned.
        const DISABLED = 0;
        /// Enable synthetic bold. Font resolution finds the closest bold variant, the difference is added using extra stroke.
        const BOLD = 1;
        /// Enable synthetic oblique. If the font resolution does not find an oblique or italic variant a skew transform is applied.
        const OBLIQUE = 2;
        /// Enabled all synthetic font possibilities.
        const ENABLED = Self::BOLD.bits() | Self::OBLIQUE.bits();
    }
}
impl Default for FontSynthesis {
    /// [`FontSynthesis::ENABLED`]
    fn default() -> Self {
        FontSynthesis::ENABLED
    }
}
impl_from_and_into_var! {
    /// Convert to full [`ENABLED`](FontSynthesis::ENABLED) or [`DISABLED`](FontSynthesis::DISABLED).
    fn from(enabled: bool) -> FontSynthesis {
        if enabled { FontSynthesis::ENABLED } else { FontSynthesis::DISABLED }
    }
}