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/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,