Bug 1836063 - Add invalidation regression test r=gfx-reviewers,gw

Add a regression test for picture cache invalidation caused by scrolling
content with opacity-filtered stacking contexts.  This test ensures that
picture cache tiles are not invalidated by scrolling when such
sub-pictures are present, which was the problem in bug 1836063.

Depends on D181664

Differential Revision: https://phabricator.services.mozilla.com/D182496

gfx/wr/wrench/invalidation/scroll_subpic_1.yaml

@@ -0,0 +1,29 @@
+# This is intended to be a really simple imitation of what Gecko's
+# display-list around the content scrolling viewport.  In addition to the
+# scroll-frame's clip (added by clip-to-frame) it also adds equivalent clips
+# to everything inside, including inside the stacking context.  The stacking
+# context with partial opacity acts as a regression test for bug 1836063.
+
+root:
+  items:
+    - type: clip
+      id: 2
+      bounds: [0, 0, 50, 50]
+    - type: clip-chain
+      id: 3
+      clips: [2]
+
+    - type: scroll-frame
+      bounds: [0, 0, 50, 50]
+      scroll-offset: [0, 0]
+      clip-to-frame: true
+      items:
+        - type: stacking-context
+          bounds: [0, 0, 100, 500]
+          filters: [opacity(0.9)]
+          clip-chain: 3
+          items:
+            - type: rect
+              bounds: [0, 0, 100, 500]
+              color: green
+              clip-chain: 3

gfx/wr/wrench/invalidation/scroll_subpic_2.yaml

@@ -0,0 +1,26 @@
+# This file should be identical to scroll_subpic_1.yaml except for the
+# scroll-offset on the scroll-frame.
+
+root:
+  items:
+    - type: clip
+      id: 2
+      bounds: [0, 0, 50, 50]
+    - type: clip-chain
+      id: 3
+      clips: [2]
+
+    - type: scroll-frame
+      bounds: [0, 0, 50, 50]
+      scroll-offset: [0, 10]
+      clip-to-frame: true
+      items:
+        - type: stacking-context
+          bounds: [0, 0, 100, 500]
+          filters: [opacity(0.9)]
+          clip-chain: 3
+          items:
+            - type: rect
+              bounds: [0, 0, 100, 500]
+              color: green
+              clip-chain: 3

gfx/wr/wrench/src/test_invalidation.rs

@@ -50,6 +50,7 @@ impl<'a> TestHarness<'a> {
         // List all invalidation tests here
         self.test_basic();
         self.test_composite_nop();
+        self.test_scroll_subpic();
     }
 
     /// Simple validation / proof of concept of invalidation testing
@@ -105,6 +106,29 @@ impl<'a> TestHarness<'a> {
         assert!(results.composite_needed);
     }
 
+    /// Ensure that tile cache pictures are not invalidated upon scrolling
+    fn test_scroll_subpic(
+        &mut self,
+    ) {
+        // First frame at scroll-offset 0
+        let results = self.render_yaml("scroll_subpic_1");
+
+        // Ensure we actually rendered something
+        assert!(
+            matches!(results.pc_debug.slice(0).tile(0, 0), TileDebugInfo::Dirty(..)),
+            "Ensure the first test frame actually rendered something",
+        );
+
+        // Second frame just scrolls to scroll-offset 50
+        let results = self.render_yaml("scroll_subpic_2");
+
+        // Ensure the cache tile was not invalidated
+        assert!(
+            results.pc_debug.slice(0).tile(0, 0).is_valid(),
+            "Ensure the cache tile was not invalidated after scrolling",
+        );
+    }
+
     /// Render a YAML file, and return the picture cache debug info
     fn render_yaml(
         &mut self,