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>

Cargo.lock

@@ -1426,6 +1426,7 @@ dependencies = [
  "profile_traits",
  "raw-window-handle",
  "serde",
+ "servo_geometry",
  "servo_malloc_size_of",
  "smallvec",
  "strum_macros",

components/compositing/compositor.rs

@@ -227,6 +227,11 @@ pub(crate) struct PipelineDetails {
     /// The paint metric status of the first contentful paint.
     pub first_contentful_paint_metric: PaintMetricState,
 
+    /// The CSS pixel to device pixel scale of the viewport of this pipeline, including
+    /// page zoom, but not including any pinch zoom amount. This is used to detect
+    /// situations where the current display list is for an old scale.
+    pub viewport_scale: Option<Scale<f32, CSSPixel, DevicePixel>>,
+
     /// Which parts of Servo have reported that this `Pipeline` has exited. Only when all
     /// have done so will it be discarded.
     pub exited: PipelineExitSource,
@@ -248,6 +253,7 @@ impl PipelineDetails {
             pipeline: None,
             parent_pipeline_id: None,
             most_recent_display_list_epoch: None,
+            viewport_scale: None,
             animations_running: false,
             animation_callbacks_running: false,
             throttled: false,
@@ -761,14 +767,18 @@ impl IOCompositor {
                 let Some(webview_renderer) = self.webview_renderers.get_mut(webview_id) else {
                     return warn!("Could not find WebView for incoming display list");
                 };
+
                 // WebRender is not ready until we receive "NewWebRenderFrameReady"
                 webview_renderer.webrender_frame_ready.set(false);
+                let old_scale = webview_renderer.device_pixels_per_page_pixel();
 
                 let pipeline_id = display_list_info.pipeline_id;
                 let details = webview_renderer.ensure_pipeline_details(pipeline_id.into());
                 details.most_recent_display_list_epoch = Some(display_list_info.epoch);
                 details.hit_test_items = display_list_info.hit_test_info;
                 details.install_new_scroll_tree(display_list_info.scroll_tree);
+                details.viewport_scale =
+                    Some(display_list_info.viewport_details.hidpi_scale_factor);
 
                 let epoch = display_list_info.epoch;
                 let first_reflow = display_list_info.first_reflow;
@@ -783,6 +793,14 @@ impl IOCompositor {
                 }
 
                 let mut transaction = Transaction::new();
+
+                let is_root_pipeline =
+                    Some(pipeline_id.into()) == webview_renderer.root_pipeline_id;
+                if is_root_pipeline && old_scale != webview_renderer.device_pixels_per_page_pixel()
+                {
+                    self.send_root_pipeline_display_list_in_transaction(&mut transaction);
+                }
+
                 transaction
                     .set_display_list(display_list_info.epoch, (pipeline_id, built_display_list));
                 self.update_transaction_with_all_scroll_offsets(&mut transaction);
@@ -1227,9 +1245,8 @@ impl IOCompositor {
         }
 
         if let Some(webview_renderer) = self.webview_renderers.get_mut(webview_id) {
-            webview_renderer.set_page_zoom(1.0);
+            webview_renderer.set_page_zoom(Scale::new(1.0));
         }
-        self.send_root_pipeline_display_list();
     }
 
     pub fn on_zoom_window_event(&mut self, webview_id: WebViewId, magnification: f32) {
@@ -1238,9 +1255,9 @@ impl IOCompositor {
         }
 
         if let Some(webview_renderer) = self.webview_renderers.get_mut(webview_id) {
-            webview_renderer.set_page_zoom(magnification);
+            let current_page_zoom = webview_renderer.page_zoom();
+            webview_renderer.set_page_zoom(current_page_zoom * Scale::new(magnification));
         }
-        self.send_root_pipeline_display_list();
     }
 
     fn details_for_pipeline(&self, pipeline_id: PipelineId) -> Option<&PipelineDetails> {

components/compositing/webview_renderer.rs

@@ -10,7 +10,7 @@ use std::rc::Rc;
 use base::id::{PipelineId, WebViewId};
 use compositing_traits::display_list::ScrollType;
 use compositing_traits::viewport_description::{
-    DEFAULT_ZOOM, MAX_ZOOM, MIN_ZOOM, ViewportDescription,
+    DEFAULT_PAGE_ZOOM, MAX_PAGE_ZOOM, MIN_PAGE_ZOOM, ViewportDescription,
 };
 use compositing_traits::{PipelineExitSource, SendableFrameTree, WebViewTrait};
 use constellation_traits::{EmbedderToConstellationMessage, WindowSizeType};
@@ -100,7 +100,8 @@ pub(crate) struct WebViewRenderer {
     pending_point_input_events: RefCell<VecDeque<InputEvent>>,
     /// WebRender is not ready between `SendDisplayList` and `WebRenderFrameReady` messages.
     pub webrender_frame_ready: Cell<bool>,
-    /// Viewport Description
+    /// A [`ViewportDescription`] for this [`WebViewRenderer`], which contains the limitations
+    /// and initial values for zoom derived from the `viewport` meta tag in web content.
     viewport_description: Option<ViewportDescription>,
 }
 
@@ -130,8 +131,8 @@ impl WebViewRenderer {
             touch_handler: TouchHandler::new(),
             global,
             pending_scroll_zoom_events: Default::default(),
-            page_zoom: Scale::new(DEFAULT_ZOOM),
-            pinch_zoom: PinchZoomFactor::new(DEFAULT_ZOOM),
+            page_zoom: DEFAULT_PAGE_ZOOM,
+            pinch_zoom: PinchZoomFactor::new(1.0),
             hidpi_scale_factor: Scale::new(hidpi_scale_factor.0),
             animating: false,
             pending_point_input_events: Default::default(),
@@ -964,15 +965,39 @@ impl WebViewRenderer {
         old_zoom != self.pinch_zoom
     }
 
-    pub(crate) fn set_page_zoom(&mut self, magnification: f32) {
-        self.page_zoom =
-            Scale::new((self.page_zoom.get() * magnification).clamp(MIN_ZOOM, MAX_ZOOM));
+    pub(crate) fn page_zoom(&mut self) -> Scale<f32, CSSPixel, DeviceIndependentPixel> {
+        self.page_zoom
     }
 
+    pub(crate) fn set_page_zoom(
+        &mut self,
+        new_page_zoom: Scale<f32, CSSPixel, DeviceIndependentPixel>,
+    ) {
+        let new_page_zoom = new_page_zoom.clamp(MIN_PAGE_ZOOM, MAX_PAGE_ZOOM);
+        let old_zoom = std::mem::replace(&mut self.page_zoom, new_page_zoom);
+        if old_zoom != self.page_zoom {
+            self.send_window_size_message();
+        }
+    }
+
+    /// The scale to use when displaying this [`WebViewRenderer`] in WebRender
+    /// including both viewport scale (page zoom and hidpi scale) as well as any
+    /// pinch zoom applied. This is based on the latest display list received,
+    /// as page zoom changes are applied asynchronously and the rendered view
+    /// should reflect the latest display list.
     pub(crate) fn device_pixels_per_page_pixel(&self) -> Scale<f32, CSSPixel, DevicePixel> {
-        self.page_zoom * self.hidpi_scale_factor * self.pinch_zoom_level()
+        let viewport_scale = self
+            .root_pipeline_id
+            .and_then(|pipeline_id| self.pipelines.get(&pipeline_id))
+            .and_then(|pipeline| pipeline.viewport_scale)
+            .unwrap_or_else(|| self.page_zoom * self.hidpi_scale_factor);
+        viewport_scale * self.pinch_zoom_level()
     }
 
+    /// The current viewport scale (hidpi scale and page zoom and not pinch
+    /// zoom) based on the current setting of the WebView. Note that this may
+    /// not be the rendered viewport zoom as that is based on the latest display
+    /// list and zoom changes are applied asynchronously.
     pub(crate) fn device_pixels_per_page_pixel_not_including_pinch_zoom(
         &self,
     ) -> Scale<f32, CSSPixel, DevicePixel> {

components/layout/display_list/background.rs

@@ -65,7 +65,11 @@ impl<'a> BackgroundPainter<'a> {
         if &BackgroundAttachment::Fixed ==
             get_cyclic(&background.background_attachment.0, layer_index)
         {
-            return builder.compositor_info.viewport_size.into();
+            return builder
+                .compositor_info
+                .viewport_details
+                .layout_size()
+                .into();
         }
 
         match get_cyclic(&background.background_clip.0, layer_index) {
@@ -149,7 +153,11 @@ impl<'a> BackgroundPainter<'a> {
                 Origin::PaddingBox => *fragment_builder.padding_rect(),
                 Origin::BorderBox => fragment_builder.border_rect,
             },
-            BackgroundAttachment::Fixed => builder.compositor_info.viewport_size.into(),
+            BackgroundAttachment::Fixed => builder
+                .compositor_info
+                .viewport_details
+                .layout_size()
+                .into(),
         }
     }
 }

components/layout/display_list/stacking_context.rs

@@ -14,6 +14,7 @@ use compositing_traits::display_list::{
     AxesScrollSensitivity, CompositorDisplayListInfo, ReferenceFrameNodeInfo, ScrollableNodeInfo,
     SpatialTreeNodeInfo, StickyNodeInfo,
 };
+use embedder_traits::ViewportDetails;
 use euclid::SideOffsets2D;
 use euclid::default::{Point2D, Rect, Size2D};
 use log::warn;
@@ -120,7 +121,7 @@ impl StackingContextTree {
     /// pipeline id.
     pub fn new(
         fragment_tree: &FragmentTree,
-        viewport_size: LayoutSize,
+        viewport_details: ViewportDetails,
         pipeline_id: wr::PipelineId,
         first_reflow: bool,
         debug: &DebugOptions,
@@ -131,8 +132,9 @@ impl StackingContextTree {
             scrollable_overflow.size.height.to_f32_px(),
         ));
 
+        let viewport_size = viewport_details.layout_size();
         let compositor_info = CompositorDisplayListInfo::new(
-            viewport_size,
+            viewport_details,
             scrollable_overflow,
             pipeline_id,
             // This epoch is set when the WebRender display list is built. For now use a dummy value.
@@ -145,7 +147,7 @@ impl StackingContextTree {
         let cb_for_non_fixed_descendants = ContainingBlock::new(
             fragment_tree.initial_containing_block,
             root_scroll_node_id,
-            Some(compositor_info.viewport_size),
+            Some(viewport_size),
             ClipId::INVALID,
         );
         let cb_for_fixed_descendants = ContainingBlock::new(
@@ -1504,7 +1506,10 @@ impl BoxFragment {
             Some(size) => size,
             None => {
                 // This is a direct descendant of a reference frame.
-                &stacking_context_tree.compositor_info.viewport_size
+                &stacking_context_tree
+                    .compositor_info
+                    .viewport_details
+                    .layout_size()
             },
         };
 

components/layout/layout_impl.rs

@@ -75,7 +75,7 @@ use style::{Zero, driver};
 use style_traits::{CSSPixel, SpeculativePainter};
 use stylo_atoms::Atom;
 use url::Url;
-use webrender_api::units::{DevicePixel, DevicePoint, LayoutSize, LayoutVector2D};
+use webrender_api::units::{DevicePixel, DevicePoint, LayoutVector2D};
 use webrender_api::{ExternalScrollId, HitTestFlags};
 
 use crate::context::{CachedImageOrError, ImageResolver, LayoutContext};
@@ -960,12 +960,6 @@ impl LayoutThread {
             return;
         }
 
-        let viewport_size = self.stylist.device().au_viewport_size();
-        let viewport_size = LayoutSize::new(
-            viewport_size.width.to_f32_px(),
-            viewport_size.height.to_f32_px(),
-        );
-
         let mut stacking_context_tree = self.stacking_context_tree.borrow_mut();
         let old_scroll_offsets = stacking_context_tree
             .as_ref()
@@ -976,7 +970,7 @@ impl LayoutThread {
         // applicable spatial and clip nodes.
         let mut new_stacking_context_tree = StackingContextTree::new(
             fragment_tree,
-            viewport_size,
+            reflow_request.viewport_details,
             self.id.into(),
             !self.have_ever_generated_display_list.get(),
             &self.debug,

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)]