layout: Use FastTransform for hit testing (#38554)

`FastTransform` provides faster matrix operations when the involved
transforms are just translations.

Testing: Not needed (no change in behavior)

Signed-off-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>

Cargo.lock

@@ -6222,7 +6222,7 @@ dependencies = [
 [[package]]
 name = "peek-poke"
 version = "0.3.0"
-source = "git+https://github.com/servo/webrender?branch=0.67#ae2477d9a6da403e5b5dce8a17415a2cd1563074"
+source = "git+https://github.com/servo/webrender?branch=0.67#15318d6627e91ec19fc0a44a7434b08673413140"
 dependencies = [
  "euclid",
  "peek-poke-derive",
@@ -6231,7 +6231,7 @@ dependencies = [
 [[package]]
 name = "peek-poke-derive"
 version = "0.3.0"
-source = "git+https://github.com/servo/webrender?branch=0.67#ae2477d9a6da403e5b5dce8a17415a2cd1563074"
+source = "git+https://github.com/servo/webrender?branch=0.67#15318d6627e91ec19fc0a44a7434b08673413140"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -7666,6 +7666,7 @@ dependencies = [
  "euclid",
  "malloc_size_of_derive",
  "servo_malloc_size_of",
+ "webrender",
  "webrender_api",
 ]
 
@@ -9656,7 +9657,7 @@ dependencies = [
 [[package]]
 name = "webrender"
 version = "0.66.0"
-source = "git+https://github.com/servo/webrender?branch=0.67#ae2477d9a6da403e5b5dce8a17415a2cd1563074"
+source = "git+https://github.com/servo/webrender?branch=0.67#15318d6627e91ec19fc0a44a7434b08673413140"
 dependencies = [
  "allocator-api2",
  "bincode",
@@ -9691,7 +9692,7 @@ dependencies = [
 [[package]]
 name = "webrender_api"
 version = "0.66.0"
-source = "git+https://github.com/servo/webrender?branch=0.67#ae2477d9a6da403e5b5dce8a17415a2cd1563074"
+source = "git+https://github.com/servo/webrender?branch=0.67#15318d6627e91ec19fc0a44a7434b08673413140"
 dependencies = [
  "app_units",
  "bitflags 2.9.1",
@@ -9712,7 +9713,7 @@ dependencies = [
 [[package]]
 name = "webrender_build"
 version = "0.0.2"
-source = "git+https://github.com/servo/webrender?branch=0.67#ae2477d9a6da403e5b5dce8a17415a2cd1563074"
+source = "git+https://github.com/servo/webrender?branch=0.67#15318d6627e91ec19fc0a44a7434b08673413140"
 dependencies = [
  "bitflags 2.9.1",
  "lazy_static",
@@ -10424,7 +10425,7 @@ dependencies = [
 [[package]]
 name = "wr_glyph_rasterizer"
 version = "0.1.0"
-source = "git+https://github.com/servo/webrender?branch=0.67#ae2477d9a6da403e5b5dce8a17415a2cd1563074"
+source = "git+https://github.com/servo/webrender?branch=0.67#15318d6627e91ec19fc0a44a7434b08673413140"
 dependencies = [
  "core-foundation 0.9.4",
  "core-graphics",
@@ -10449,7 +10450,7 @@ dependencies = [
 [[package]]
 name = "wr_malloc_size_of"
 version = "0.2.0"
-source = "git+https://github.com/servo/webrender?branch=0.67#ae2477d9a6da403e5b5dce8a17415a2cd1563074"
+source = "git+https://github.com/servo/webrender?branch=0.67#15318d6627e91ec19fc0a44a7434b08673413140"
 dependencies = [
  "app_units",
  "euclid",

components/geometry/Cargo.toml

@@ -16,4 +16,5 @@ app_units = { workspace = true }
 euclid = { workspace = true }
 malloc_size_of = { workspace = true }
 malloc_size_of_derive = { workspace = true }
+webrender = { workspace = true }
 webrender_api = { workspace = true }

components/geometry/lib.rs

@@ -8,9 +8,10 @@ use app_units::{Au, MAX_AU, MIN_AU};
 use euclid::default::{Point2D as UntypedPoint2D, Rect as UntypedRect, Size2D as UntypedSize2D};
 use euclid::{Box2D, Length, Point2D, Scale, SideOffsets2D, Size2D, Vector2D};
 use malloc_size_of_derive::MallocSizeOf;
+use webrender::FastTransform;
 use webrender_api::units::{
-    DeviceIntRect, DeviceIntSize, DevicePixel, FramebufferPixel, LayoutPoint, LayoutRect,
-    LayoutSize,
+    DeviceIntRect, DeviceIntSize, DevicePixel, FramebufferPixel, LayoutPixel, LayoutPoint,
+    LayoutRect, LayoutSize,
 };
 
 // Units for use with euclid::length and euclid::scale_factor.
@@ -46,6 +47,8 @@ pub type DeviceIndependentPoint = Point2D<f32, DeviceIndependentPixel>;
 pub type DeviceIndependentVector2D = Vector2D<f32, DeviceIndependentPixel>;
 pub type DeviceIndependentSize = Size2D<f32, DeviceIndependentPixel>;
 
+pub type FastLayoutTransform = FastTransform<LayoutPixel, LayoutPixel>;
+
 // An Au is an "App Unit" and represents 1/60th of a CSS pixel.  It was
 // originally proposed in 2002 as a standard unit of measure in Gecko.
 // See https://bugzilla.mozilla.org/show_bug.cgi?id=177805 for more info.

components/layout/display_list/hit_test.rs

@@ -7,16 +7,17 @@ use std::collections::HashMap;
 use app_units::Au;
 use base::id::ScrollTreeNodeId;
 use embedder_traits::Cursor;
-use euclid::{Box2D, Point2D, Point3D, Vector2D};
+use euclid::{Box2D, Vector2D};
 use kurbo::{Ellipse, Shape};
 use layout_api::{ElementsFromPointFlags, ElementsFromPointResult};
+use servo_geometry::FastLayoutTransform;
 use style::computed_values::backface_visibility::T as BackfaceVisibility;
 use style::computed_values::pointer_events::T as PointerEvents;
 use style::computed_values::visibility::T as Visibility;
 use style::properties::ComputedValues;
 use style::values::computed::ui::CursorKind;
 use webrender_api::BorderRadius;
-use webrender_api::units::{LayoutPoint, LayoutRect, LayoutSize, LayoutTransform, RectExt};
+use webrender_api::units::{LayoutPoint, LayoutRect, LayoutSize, RectExt};
 
 use crate::display_list::clip::{Clip, ClipId};
 use crate::display_list::stacking_context::StackingContextSection;
@@ -33,7 +34,7 @@ pub(crate) struct HitTest<'a> {
     point_to_test: LayoutPoint,
     /// A cached version of [`Self::point_to_test`] projected to a spatial node, to avoid
     /// doing a lot of matrix math over and over.
-    projected_point_to_test: Option<(ScrollTreeNodeId, LayoutPoint, LayoutTransform)>,
+    projected_point_to_test: Option<(ScrollTreeNodeId, LayoutPoint, FastLayoutTransform)>,
     /// The stacking context tree against which to perform the hit test.
     stacking_context_tree: &'a StackingContextTree,
     /// The resulting [`HitTestResultItems`] for this hit test.
@@ -89,7 +90,7 @@ impl<'a> HitTest<'a> {
     fn location_in_spatial_node(
         &mut self,
         scroll_tree_node_id: ScrollTreeNodeId,
-    ) -> Option<(LayoutPoint, LayoutTransform)> {
+    ) -> Option<(LayoutPoint, FastLayoutTransform)> {
         match self.projected_point_to_test {
             Some((cached_scroll_tree_node_id, projected_point, transform))
                 if cached_scroll_tree_node_id == scroll_tree_node_id =>
@@ -105,21 +106,7 @@ impl<'a> HitTest<'a> {
             .scroll_tree
             .cumulative_root_to_node_transform(&scroll_tree_node_id)?;
 
-        // This comes from WebRender at `webrender/utils.rs`.
-        // See https://bugzilla.mozilla.org/show_bug.cgi?id=1765204#c3.
-        //
-        // We are going from world coordinate space to spatial node coordinate space.
-        // Normally, that transformation happens in the opposite direction, but for hit
-        // testing everything is reversed. The result of the display transformation comes
-        // with a z-coordinate that we do not have access to here.
-        //
-        // We must solve for a value of z here that transforms to 0 (the value of z for our
-        // point).
-        let point = self.point_to_test;
-        let z =
-            -(point.x * transform.m13 + point.y * transform.m23 + transform.m43) / transform.m33;
-        let projected_point = transform.transform_point3d(Point3D::new(point.x, point.y, z))?;
-        let projected_point = Point2D::new(projected_point.x, projected_point.y);
+        let projected_point = transform.project_point2d(self.point_to_test)?;
 
         self.projected_point_to_test = Some((scroll_tree_node_id, projected_point, transform));
         Some((projected_point, transform))

components/layout/display_list/mod.rs

@@ -272,7 +272,7 @@ impl DisplayListBuilder<'_> {
                         info.origin,
                         *parent_spatial_node_id,
                         info.transform_style,
-                        PropertyBinding::Value(info.transform),
+                        PropertyBinding::Value(*info.transform.to_transform()),
                         info.kind,
                         spatial_tree_item_key,
                     );

components/layout/display_list/stacking_context.rs

@@ -234,7 +234,7 @@ impl StackingContextTree {
                 origin,
                 frame_origin_for_query,
                 transform_style,
-                transform,
+                transform: transform.into(),
                 kind,
             }),
         )

components/layout/query.rs

@@ -14,7 +14,7 @@ use layout_api::wrapper_traits::{LayoutNode, ThreadSafeLayoutElement, ThreadSafe
 use layout_api::{LayoutElementType, LayoutNodeType, OffsetParentResponse};
 use script::layout_dom::ServoLayoutNode;
 use servo_arc::Arc as ServoArc;
-use servo_geometry::{au_rect_to_f32_rect, f32_rect_to_au_rect};
+use servo_geometry::{FastLayoutTransform, au_rect_to_f32_rect, f32_rect_to_au_rect};
 use servo_url::ServoUrl;
 use style::computed_values::display::T as Display;
 use style::computed_values::position::T as Position;
@@ -39,7 +39,6 @@ use style::values::specified::GenericGridTemplateComponent;
 use style::values::specified::box_::DisplayInside;
 use style::values::specified::text::TextTransformCase;
 use style_traits::{ParsingMode, ToCss};
-use webrender_api::units::LayoutTransform;
 
 use crate::ArcRefCell;
 use crate::display_list::StackingContextTree;
@@ -55,7 +54,7 @@ use crate::taffy::SpecificTaffyGridInfo;
 fn root_transform_for_layout_node(
     scroll_tree: &ScrollTree,
     node: ServoLayoutNode<'_>,
-) -> Option<LayoutTransform> {
+) -> Option<FastLayoutTransform> {
     let fragments = node.fragments_for_pseudo(None);
     let box_fragment = fragments
         .first()
@@ -90,7 +89,7 @@ pub(crate) fn process_content_box_request(
         return Some(rect_union);
     };
 
-    Some(transform_au_rectangle(rect_union, transform))
+    transform_au_rectangle(rect_union, transform)
 }
 
 pub(crate) fn process_content_boxes_request(
@@ -110,7 +109,7 @@ pub(crate) fn process_content_boxes_request(
     };
 
     content_boxes
-        .map(|rect| transform_au_rectangle(rect, transform))
+        .filter_map(|rect| transform_au_rectangle(rect, transform))
         .collect()
 }
 
@@ -1150,9 +1149,17 @@ where
     Some(computed_values.clone_font())
 }
 
-fn transform_au_rectangle(rect_to_transform: Rect<Au>, transform: LayoutTransform) -> Rect<Au> {
-    transform
-        .outer_transformed_rect(&au_rect_to_f32_rect(rect_to_transform).cast_unit())
+fn transform_au_rectangle(
+    rect_to_transform: Rect<Au>,
+    transform: FastLayoutTransform,
+) -> Option<Rect<Au>> {
+    let rect_to_transform = &au_rect_to_f32_rect(rect_to_transform).cast_unit();
+    let outer_transformed_rect = match transform {
+        FastLayoutTransform::Offset(offset) => Some(rect_to_transform.translate(offset)),
+        FastLayoutTransform::Transform { transform, .. } => {
+            transform.outer_transformed_rect(rect_to_transform)
+        },
+    };
+    outer_transformed_rect
         .map(|transformed_rect| f32_rect_to_au_rect(transformed_rect.to_untyped()))
-        .unwrap_or(rect_to_transform)
 }

components/shared/compositing/display_list.rs

@@ -11,13 +11,12 @@ use base::id::ScrollTreeNodeId;
 use base::print_tree::PrintTree;
 use bitflags::bitflags;
 use embedder_traits::ViewportDetails;
-use euclid::{SideOffsets2D, Transform3D};
+use euclid::SideOffsets2D;
 use malloc_size_of_derive::MallocSizeOf;
 use serde::{Deserialize, Serialize};
+use servo_geometry::FastLayoutTransform;
 use style::values::specified::Overflow;
-use webrender_api::units::{
-    LayoutPixel, LayoutPoint, LayoutRect, LayoutSize, LayoutTransform, LayoutVector2D,
-};
+use webrender_api::units::{LayoutPixel, LayoutPoint, LayoutRect, LayoutSize, LayoutVector2D};
 use webrender_api::{
     Epoch, ExternalScrollId, PipelineId, ReferenceFrameKind, ScrollLocation, SpatialId,
     StickyOffsetBounds, TransformStyle,
@@ -167,7 +166,7 @@ pub struct ReferenceFrameNodeInfo {
     /// Origin of this frame relative to the document for bounding box queries.
     pub frame_origin_for_query: LayoutPoint,
     pub transform_style: TransformStyle,
-    pub transform: LayoutTransform,
+    pub transform: FastLayoutTransform,
     pub kind: ReferenceFrameKind,
 }
 
@@ -281,8 +280,8 @@ impl ScrollableNodeInfo {
 ///    multiplication when transforms are not involved.
 #[derive(Clone, Copy, Debug, Default, Deserialize, Serialize)]
 pub struct ScrollTreeNodeTransformationCache {
-    node_to_root_transform: LayoutTransform,
-    root_to_node_transform: Option<LayoutTransform>,
+    node_to_root_transform: FastLayoutTransform,
+    root_to_node_transform: Option<FastLayoutTransform>,
 }
 
 #[derive(Default)]
@@ -604,7 +603,10 @@ impl ScrollTree {
 
     /// Find a transformation that can convert a point in the node coordinate system to a
     /// point in the root coordinate system.
-    pub fn cumulative_node_to_root_transform(&self, node_id: &ScrollTreeNodeId) -> LayoutTransform {
+    pub fn cumulative_node_to_root_transform(
+        &self,
+        node_id: &ScrollTreeNodeId,
+    ) -> FastLayoutTransform {
         let node = self.get_node(node_id);
         if let Some(cached_transforms) = node.transformation_cache.get() {
             return cached_transforms.node_to_root_transform;
@@ -621,7 +623,7 @@ impl ScrollTree {
     pub fn cumulative_root_to_node_transform(
         &self,
         node_id: &ScrollTreeNodeId,
-    ) -> Option<LayoutTransform> {
+    ) -> Option<FastLayoutTransform> {
         let node = self.get_node(node_id);
         if let Some(cached_transforms) = node.transformation_cache.get() {
             return cached_transforms.root_to_node_transform;
@@ -642,25 +644,16 @@ impl ScrollTree {
             None => (Default::default(), Default::default()),
         };
 
-        let change_basis =
-            |transform: &Transform3D<f32, LayoutPixel, LayoutPixel>, x: f32, y: f32| {
-                let pre_translation = Transform3D::translation(x, y, 0.0);
-                let post_translation = Transform3D::translation(-x, -y, 0.0);
-                post_translation.then(transform).then(&pre_translation)
-            };
-
         let (node_to_parent_transform, parent_to_node_transform) = match &node.info {
             SpatialTreeNodeInfo::ReferenceFrame(info) => {
                 // To apply a transformation we need to make sure the rectangle's
                 // coordinate space is the same as reference frame's coordinate space.
-                let node_to_parent_transform = change_basis(
-                    &info.transform,
-                    info.frame_origin_for_query.x,
-                    info.frame_origin_for_query.y,
-                );
+                let offset = info.frame_origin_for_query.to_vector();
+                let node_to_parent_transform =
+                    info.transform.pre_translate(-offset).then_translate(offset);
 
                 let parent_to_node_transform =
-                    Transform3D::translation(-info.origin.x, -info.origin.y, 0.0);
+                    FastLayoutTransform::Offset(-info.origin.to_vector());
                 let parent_to_node_transform = info
                     .transform
                     .inverse()
@@ -675,20 +668,15 @@ impl ScrollTree {
             SpatialTreeNodeInfo::Scroll(info) => {
                 sticky_info.nearest_scrolling_ancestor_viewport = info.clip_rect;
                 sticky_info.nearest_scrolling_ancestor_offset = -info.offset;
-
-                (
-                    Transform3D::translation(-info.offset.x, -info.offset.y, 0.0),
-                    Some(Transform3D::translation(info.offset.x, info.offset.y, 0.0)),
-                )
+                let offset_transform = FastLayoutTransform::Offset(-info.offset);
+                (offset_transform, offset_transform.inverse())
             },
 
             SpatialTreeNodeInfo::Sticky(info) => {
                 let offset = info.calculate_sticky_offset(&sticky_info);
                 sticky_info.nearest_scrolling_ancestor_offset += offset;
-                (
-                    Transform3D::translation(offset.x, offset.y, 0.0),
-                    Some(Transform3D::translation(-offset.x, -offset.y, 0.0)),
-                )
+                let offset_transform = FastLayoutTransform::Offset(offset);
+                (offset_transform, offset_transform.inverse())
             },
         };
 
@@ -845,7 +833,7 @@ impl CompositorDisplayListInfo {
                 origin: Default::default(),
                 frame_origin_for_query: Default::default(),
                 transform_style: TransformStyle::Flat,
-                transform: LayoutTransform::identity(),
+                transform: FastLayoutTransform::identity(),
                 kind: ReferenceFrameKind::default(),
             }),
         );