compositor: Request reflow when doing a page zooming (#38166)

Request a reflow when doing page zoom and only modify the scaling of the
WebView scene after the first root pipeline display list with the new
zoom is ready. In addition:

  - store zoom limits in `Scale` types
  - send `ViewportDetails` along with the display list so that we can
    detect when the root pipeline scale is ready.

Testing: This is quite hard to test as it requires verification that
contents are zoomed appropriately at the right time.
Fixes: #38091.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

components/shared/compositing/Cargo.toml

@@ -32,6 +32,7 @@ malloc_size_of_derive = { workspace = true }
 profile_traits = { path = '../profile' }
 raw-window-handle = { version = "0.6" }
 serde = { workspace = true }
+servo_geometry = { path = "../../geometry" }
 smallvec = { workspace = true }
 strum_macros = { workspace = true }
 stylo = { workspace = true }

components/shared/compositing/display_list.rs

@@ -9,7 +9,7 @@ use std::collections::HashMap;
 use base::id::ScrollTreeNodeId;
 use base::print_tree::PrintTree;
 use bitflags::bitflags;
-use embedder_traits::Cursor;
+use embedder_traits::{Cursor, ViewportDetails};
 use euclid::SideOffsets2D;
 use malloc_size_of_derive::MallocSizeOf;
 use serde::{Deserialize, Serialize};
@@ -486,8 +486,9 @@ pub struct CompositorDisplayListInfo {
     /// The WebRender [PipelineId] of this display list.
     pub pipeline_id: PipelineId,
 
-    /// The size of the viewport that this display list renders into.
-    pub viewport_size: LayoutSize,
+    /// The [`ViewportDetails`] that describe the viewport in the script/layout thread at
+    /// the time this display list was created.
+    pub viewport_details: ViewportDetails,
 
     /// The size of this display list's content.
     pub content_size: LayoutSize,
@@ -526,7 +527,7 @@ impl CompositorDisplayListInfo {
     /// Create a new CompositorDisplayListInfo with the root reference frame
     /// and scroll frame already added to the scroll tree.
     pub fn new(
-        viewport_size: LayoutSize,
+        viewport_details: ViewportDetails,
         content_size: LayoutSize,
         pipeline_id: PipelineId,
         epoch: Epoch,
@@ -548,7 +549,10 @@ impl CompositorDisplayListInfo {
             SpatialTreeNodeInfo::Scroll(ScrollableNodeInfo {
                 external_id: ExternalScrollId(0, pipeline_id),
                 content_rect: LayoutRect::from_origin_and_size(LayoutPoint::zero(), content_size),
-                clip_rect: LayoutRect::from_origin_and_size(LayoutPoint::zero(), viewport_size),
+                clip_rect: LayoutRect::from_origin_and_size(
+                    LayoutPoint::zero(),
+                    viewport_details.layout_size(),
+                ),
                 scroll_sensitivity: viewport_scroll_sensitivity,
                 offset: LayoutVector2D::zero(),
             }),
@@ -556,7 +560,7 @@ impl CompositorDisplayListInfo {
 
         CompositorDisplayListInfo {
             pipeline_id,
-            viewport_size,
+            viewport_details,
             content_size,
             epoch,
             hit_test_info: Default::default(),

components/shared/compositing/viewport_description.rs

@@ -7,17 +7,19 @@
 use std::collections::HashMap;
 use std::str::FromStr;
 
-use euclid::default::Scale;
+use euclid::Scale;
 use serde::{Deserialize, Serialize};
+use servo_geometry::DeviceIndependentPixel;
+use style_traits::CSSPixel;
 
 /// Default viewport constraints
 ///
 /// <https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag#initial-scale>
-pub const MIN_ZOOM: f32 = 0.1;
+pub const MIN_PAGE_ZOOM: Scale<f32, CSSPixel, DeviceIndependentPixel> = Scale::new(0.1);
 /// <https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag#initial-scale>
-pub const MAX_ZOOM: f32 = 10.0;
+pub const MAX_PAGE_ZOOM: Scale<f32, CSSPixel, DeviceIndependentPixel> = Scale::new(10.0);
 /// <https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag#initial-scale>
-pub const DEFAULT_ZOOM: f32 = 1.0;
+pub const DEFAULT_PAGE_ZOOM: Scale<f32, CSSPixel, DeviceIndependentPixel> = Scale::new(1.0);
 
 /// <https://drafts.csswg.org/css-viewport/#parsing-algorithm>
 const SEPARATORS: [char; 2] = [',', ';']; // Comma (0x2c) and Semicolon (0x3b)
@@ -35,15 +37,15 @@ pub struct ViewportDescription {
     // TODO: height Needs to be implemented
     /// <https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag#initial-scale>
     /// the zoom level when the page is first loaded
-    pub initial_scale: Scale<f32>,
+    pub initial_scale: Scale<f32, CSSPixel, DeviceIndependentPixel>,
 
     /// <https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag#minimum_scale>
     /// how much zoom out is allowed on the page.
-    pub minimum_scale: Scale<f32>,
+    pub minimum_scale: Scale<f32, CSSPixel, DeviceIndependentPixel>,
 
     /// <https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag#maximum_scale>
     /// how much zoom in is allowed on the page
-    pub maximum_scale: Scale<f32>,
+    pub maximum_scale: Scale<f32, CSSPixel, DeviceIndependentPixel>,
 
     /// <https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag#user_scalable>
     /// whether zoom in and zoom out actions are allowed on the page
@@ -85,9 +87,9 @@ impl TryFrom<&str> for UserScalable {
 impl Default for ViewportDescription {
     fn default() -> Self {
         ViewportDescription {
-            initial_scale: Scale::new(DEFAULT_ZOOM),
-            minimum_scale: Scale::new(MIN_ZOOM),
-            maximum_scale: Scale::new(MAX_ZOOM),
+            initial_scale: DEFAULT_PAGE_ZOOM,
+            minimum_scale: MIN_PAGE_ZOOM,
+            maximum_scale: MAX_PAGE_ZOOM,
             user_scalable: UserScalable::Yes,
         }
     }
@@ -126,7 +128,9 @@ impl ViewportDescription {
     }
 
     /// Parses a viewport zoom value.
-    fn parse_viewport_value_as_zoom(value: &str) -> Option<Scale<f32>> {
+    fn parse_viewport_value_as_zoom(
+        value: &str,
+    ) -> Option<Scale<f32, CSSPixel, DeviceIndependentPixel>> {
         value
             .to_lowercase()
             .as_str()

components/shared/embedder/lib.rs

@@ -38,7 +38,7 @@ use style::queries::values::PrefersColorScheme;
 use style_traits::CSSPixel;
 use url::Url;
 use uuid::Uuid;
-use webrender_api::units::{DeviceIntPoint, DeviceIntRect, DeviceIntSize, DevicePixel};
+use webrender_api::units::{DeviceIntPoint, DeviceIntRect, DeviceIntSize, DevicePixel, LayoutSize};
 
 pub use crate::input_events::*;
 pub use crate::webdriver::*;
@@ -319,6 +319,14 @@ pub struct ViewportDetails {
     pub hidpi_scale_factor: Scale<f32, CSSPixel, DevicePixel>,
 }
 
+impl ViewportDetails {
+    /// Convert this [`ViewportDetails`] size to a [`LayoutSize`]. This is the same numerical
+    /// value as [`Self::size`], because a `LayoutPixel` is the same as a `CSSPixel`.
+    pub fn layout_size(&self) -> LayoutSize {
+        Size2D::from_untyped(self.size.to_untyped())
+    }
+}
+
 /// Unlike [`ScreenGeometry`], the data is in device-independent pixels
 /// to be used by DOM APIs
 #[derive(Default, Deserialize, Serialize)]