Bug 1766501 - Make backdrop-filter blurs use Duplicate for edgeMode r=gfx-reviewers,lsalzman

Differential Revision: https://phabricator.services.mozilla.com/D145682

gfx/wr/webrender/src/scene_building.rs

@@ -2456,6 +2456,7 @@ impl<'a> SceneBuilder<'a> {
             stacking_context.composite_ops.filters,
             stacking_context.composite_ops.filter_primitives,
             stacking_context.composite_ops.filter_datas,
+            None,
         );
 
         // Same for mix-blend-mode, except we can skip if this primitive is the first in the parent
@@ -3615,6 +3616,7 @@ impl<'a> SceneBuilder<'a> {
             filters,
             filter_primitives,
             filter_datas,
+            Some(false),
         );
 
         // Clip the backdrop filter to the outline of the backdrop-filter prim. If this is
@@ -3661,6 +3663,7 @@ impl<'a> SceneBuilder<'a> {
         mut filter_ops: Vec<Filter>,
         mut filter_primitives: Vec<FilterPrimitive>,
         filter_datas: Vec<FilterData>,
+        should_inflate_override: Option<bool>,
     ) -> PictureChainBuilder {
         // TODO(cbrewster): Currently CSS and SVG filters live side by side in WebRender, but unexpected results will
         // happen if they are used simulataneously. Gecko only provides either filter ops or filter primitives.
@@ -3704,7 +3707,18 @@ impl<'a> SceneBuilder<'a> {
                     if filter.is_noop() {
                         continue;
                     } else {
-                        PictureCompositeMode::Filter(filter.clone())
+                        let mut filter = filter.clone();
+
+                        // backdrop-filter spec says that blurs should assume edgeMode=Duplicate
+                        // We can do this by not inflating the bounds, which means the blur
+                        // shader will duplicate pixels outside the sample rect
+                        if let Some(should_inflate_override) = should_inflate_override {
+                            if let Filter::Blur { ref mut should_inflate, .. } = filter {
+                                *should_inflate = should_inflate_override;
+                            }
+                        }
+
+                        PictureCompositeMode::Filter(filter)
                     }
                 }
             };

gfx/wr/wrench/reftests/filters/backdrop-filter-blur-edge-mode-ref.yaml

@@ -0,0 +1,10 @@
+# Verify that blurs on backdrop-filters use edgeMode=duplicate
+---
+root:
+  items:
+    - type: rect
+      bounds: 0 0 400 400
+      color: red
+    - type: rect
+      bounds: 100 100 200 200
+      color: blue

gfx/wr/wrench/reftests/filters/backdrop-filter-blur-edge-mode.yaml

@@ -0,0 +1,17 @@
+# Verify that blurs on backdrop-filters use edgeMode=duplicate
+---
+root:
+  items:
+    - type: stacking-context
+      backdrop-root: true
+      bounds: 0 0 0 0
+      items:
+      - type: rect
+        bounds: 0 0 400 400
+        color: red
+      - type: rect
+        bounds: 100 100 200 200
+        color: blue
+      - type: backdrop-filter
+        bounds: 100 100 200 200
+        filters: ["blur(10,10)"]

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

@@ -69,6 +69,7 @@ fuzzy(1,1) platform(linux,mac) == svg-filter-drop-shadow-perspective.yaml svg-fi
 #platform(linux,mac) == backdrop-filter-overlap.yaml backdrop-filter-overlap.png
 #platform(linux,mac) == backdrop-filter-blur-across-tiles.yaml backdrop-filter-blur-across-tiles.png
 #platform(linux,mac) == backdrop-filter-drop-shadow.yaml backdrop-filter-drop-shadow.png
+#== backdrop-filter-blur-edge-mode.yaml backdrop-filter-blur-edge-mode-ref.yaml
 platform(linux,max) == svg-filter-offset.yaml svg-filter-offset-ref.yaml
 skip_on(android,device) == fuzzy(1,100) svg-filter-composite.yaml svg-filter-composite-ref.yaml
 skip_on(android,device) == filter-mix-blend-scaling.yaml filter-mix-blend-scaling-ref.yaml