Bug 1704478 - Ensure clips are applied to root level blend containers. r=gfx-reviewers,lsalzman

When a root level blend container matches the criteria to be optimized
from a stacking context to a tile cache, we need to ensure that if
the source stacking context had any valid clips, they are propagated
to the shared clips applied by the tile cache.

Differential Revision: https://phabricator.services.mozilla.com/D111988

gfx/wr/webrender/src/scene_building.rs

@@ -1999,6 +1999,7 @@ impl<'a> SceneBuilder<'a> {
         {
             self.tile_cache_builder.add_tile_cache(
                 stacking_context.prim_list,
+                stacking_context.clip_chain_id,
                 &self.spatial_tree,
                 &self.clip_store,
                 self.interners,

gfx/wr/webrender/src/tile_cache.rs

@@ -112,6 +112,7 @@ impl TileCacheBuilder {
     pub fn add_tile_cache(
         &mut self,
         prim_list: PrimitiveList,
+        clip_chain_id: ClipChainId,
         spatial_tree: &SpatialTree,
         clip_store: &ClipStore,
         interners: &Interners,
@@ -216,6 +217,22 @@ impl TileCacheBuilder {
             }
         }
 
+        // If a blend-container has any clips on the stacking context we are removing,
+        // we need to ensure those clips are added to the shared clips applied to the
+        // tile cache we are creating.
+        let mut current_clip_chain_id = clip_chain_id;
+        while current_clip_chain_id != ClipChainId::NONE {
+            let clip_chain_node = &clip_store
+                .clip_chain_nodes[current_clip_chain_id.0 as usize];
+
+            let clip_node_data = &interners.clip[clip_chain_node.handle];
+            if let ClipNodeKind::Rectangle = clip_node_data.clip_node_kind {
+                shared_clips.push(ClipInstance::new(clip_chain_node.handle, clip_chain_node.spatial_node_index));
+            }
+
+            current_clip_chain_id = clip_chain_node.parent_clip_chain_id;
+        }
+
         // Construct the new tile cache and add to the list to be built
         let slice = self.pending_tile_caches.len();
 

gfx/wr/wrench/reftests/clip/blend-container-ref.yaml

@@ -0,0 +1,6 @@
+---
+root:
+  items:
+    - type: rect
+      bounds: [ 50, 50, 100, 100 ]
+      color: blue

gfx/wr/wrench/reftests/clip/blend-container.yaml

@@ -0,0 +1,15 @@
+# Verify that clip-chains are correctly applied to root level blend containers (which get
+# optimized to be tile caches).
+---
+root:
+  items:
+    - type: clip
+      id: 2
+      bounds: [ 50, 50, 100, 100 ]
+    - type: stacking-context
+      blend-container: true
+      clip-node: 2
+      items:
+        - type: rect
+          bounds: [ 0, 0, 200, 200 ]
+          color: blue

gfx/wr/wrench/reftests/clip/reftest.list

@@ -18,3 +18,4 @@ color_targets(1) alpha_targets(0) == clip-out-rotation.yaml blank.yaml # Unexpec
 == iframe-nested-in-stacking-context.yaml iframe-nested-in-stacking-context-ref.yaml
 == clip-rectangle-redundant-sc.yaml clip-rectangle-redundant-sc-ref.yaml
 fuzzy(128,707) == clip-filter-raster-root.yaml clip-filter-raster-root-ref.yaml
+== blend-container.yaml blend-container-ref.yaml