Bug 1868026 - Fix compositor surface promotion with underlay + masks on translucent slices r=gfx-reviewers,lsalzman

Differential Revision: https://phabricator.services.mozilla.com/D195384

gfx/wr/webrender/src/picture.rs

@@ -2463,20 +2463,30 @@ impl TileCacheInstance {
             return SurfacePromotionResult::Failed;
         }
 
-        // For now, only support a small (arbitrary) number of compositor surfaces.
-        if surface_kind == CompositorSurfaceKind::Overlay {
-            // Non-opaque compositor surfaces require sub-slices, as they are drawn
-            // as overlays.
-            if sub_slice_index == self.sub_slices.len() - 1 {
-                return SurfacePromotionResult::Failed;
-            }
+        // Each strategy has different restrictions on whether we can promote
+        match surface_kind {
+            CompositorSurfaceKind::Overlay => {
+                // For now, only support a small (arbitrary) number of compositor surfaces.
+                // Non-opaque compositor surfaces require sub-slices, as they are drawn
+                // as overlays.
+                if sub_slice_index == self.sub_slices.len() - 1 {
+                    return SurfacePromotionResult::Failed;
+                }
 
-            // If a complex clip is being applied to this primitive, it can't be
-            // promoted directly to a compositor surface unless it's opaque (in
-            // which case we draw as an underlay + alpha cutout)
-            if prim_clip_chain.needs_mask {
-                return SurfacePromotionResult::Failed;
+                // If a complex clip is being applied to this primitive, it can't be
+                // promoted directly to a compositor surface unless it's opaque (in
+                // which case we draw as an underlay + alpha cutout)
+                if prim_clip_chain.needs_mask {
+                    return SurfacePromotionResult::Failed;
+                }
             }
+            CompositorSurfaceKind::Underlay => {
+                // Underlay strategy relies on the slice being opaque if a mask is needed
+                if prim_clip_chain.needs_mask && self.backdrop.kind.is_none() {
+                    return SurfacePromotionResult::Failed;
+                }
+            }
+            CompositorSurfaceKind::Blit => unreachable!(),
         }
 
         // If not on the root picture cache, it has some kind of

gfx/wr/wrench/reftests/compositor-surface/reftest.list

@@ -7,3 +7,4 @@ fuzzy(2,2500) == filter-overlay.yaml filter-overlay-ref.yaml
 platform(linux,mac) == mask.yaml mask.png
 platform(linux) fuzzy(7,86000) == underlay.yaml underlay.png
 fuzzy(2,2600) == transparent-opaque-image.yaml transparent-opaque-image-ref.yaml
+platform(linux) == underlay-mask-on-translucent-slice.yaml underlay-mask-on-translucent-slice.png

gfx/wr/wrench/reftests/compositor-surface/underlay-mask-on-translucent-slice.yaml

@@ -0,0 +1,24 @@
+# Verify that a compositor surface with a mask, which is placed on
+# a translucent picture cache slice draws correctly.
+---
+root:
+  items:
+    - type: rect
+      bounds: [50, 50, 440, 338]
+      color: red
+    - type: clip
+      id: 3
+      complex:
+        - rect: [70, 70, 400, 298]
+          radius: 32
+    - type: scroll-frame
+      bounds: [50, 50, 200, 200]
+      items:
+        - type: yuv-image
+          format: planar
+          src-y: barn-y.png
+          src-u: barn-u.png
+          src-v: barn-v.png
+          bounds: [70, 70, 400, 298]
+          prefer-compositor-surface: true
+          clip-chain: [3]