Changeset 288429 in webkit

Timestamp:

Jan 23, 2022 8:48:29 PM (6 months ago)

Author:

commit-queue@webkit.org

Message:

Position:fixed layers shouldn't allocate a backing buffer if all children are offscreen.
​https://bugs.webkit.org/show_bug.cgi?id=235420
<rdar://86612099>

Patch by Matt Woodrow <Matt Woodrow> on 2022-01-23
Reviewed by Simon Fraser and Darin Adler.

Source/WebCore:

Adds a bounds intersection check to isPaintDestinationForDescendantLayers,
so that we can exclude descendants that definitely won't draw anything into
the compositing layer. Uses a conservative check, which gives up if there are
any transforms in the ancestor chain.

Test: compositing/backing/no-backing-for-offscreen-children-of-position-fixed.html

• rendering/RenderLayerBacking.cpp:

(WebCore::intersectsWithAncestor):
(WebCore::RenderLayerBacking::isPaintDestinationForDescendantLayers const):

LayoutTests:

Adds a test that has a viewport sized position:fixed element (with compositing
layer), and a single child which is entirely offscreen. Tests that we correctly
determine that we don't need a backing store for the layer.

• compositing/backing/no-backing-for-offscreen-children-of-position-fixed-expected.txt: Added.
• compositing/backing/no-backing-for-offscreen-children-of-position-fixed.html: Added.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/compositing/backing/no-backing-for-offscreen-children-of-position-fixed-expected.txt (copied) (copied from trunk/LayoutTests/compositing/clip-child-by-non-stacking-ancestor-expected.txt) (1 diff)
• LayoutTests/compositing/backing/no-backing-for-offscreen-children-of-position-fixed.html (added)
• LayoutTests/compositing/clip-child-by-non-stacking-ancestor-expected.txt (modified) (1 diff)
• LayoutTests/compositing/geometry/limit-layer-bounds-fixed-expected.txt (modified) (1 diff)
• LayoutTests/platform/ios-wk2/compositing/geometry/limit-layer-bounds-fixed-expected.txt (modified) (1 diff)
• Source/WebCore/ChangeLog (modified) (1 diff)
• Source/WebCore/rendering/RenderLayerBacking.cpp (modified) (1 diff)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2022-01-23  Matt Woodrow  <mattwoodrow@apple.com>
+
+        Position:fixed layers shouldn't allocate a backing buffer if all children are offscreen.
+        https://bugs.webkit.org/show_bug.cgi?id=235420
+        <rdar://86612099>
+
+        Reviewed by Simon Fraser and Darin Adler.
+
+        Adds a test that has a viewport sized position:fixed element (with compositing
+        layer), and a single child which is entirely offscreen. Tests that we correctly
+        determine that we don't need a backing store for the layer.
+
+        * compositing/backing/no-backing-for-offscreen-children-of-position-fixed-expected.txt: Added.
+        * compositing/backing/no-backing-for-offscreen-children-of-position-fixed.html: Added.
+
 2022-01-23  Tyler Wilcock  <tyler_w@apple.com>
 

trunk/LayoutTests/compositing/backing/no-backing-for-offscreen-children-of-position-fixed-expected.txt

@@ -8 +8 @@
       (children 1
         (GraphicsLayer
-          (position 8.00 8.00)
-          (bounds 100.00 100.00)
-          (contentsOpaque 1)
-          (drawsContent 1)
+          (bounds 200.00 200.00)
         )
       )

trunk/LayoutTests/compositing/clip-child-by-non-stacking-ancestor-expected.txt

@@ -11 +11 @@
           (bounds 100.00 100.00)
           (contentsOpaque 1)
-          (drawsContent 1)
         )
       )

trunk/LayoutTests/compositing/geometry/limit-layer-bounds-fixed-expected.txt

@@ -16 +16 @@
           (position 0.00 3000.00)
           (bounds 300.00 200.00)
-          (drawsContent 1)
         )
       )

trunk/LayoutTests/platform/ios-wk2/compositing/geometry/limit-layer-bounds-fixed-expected.txt

@@ -16 +16 @@
           (position 0.00 3000.00)
           (bounds 300.00 200.00)
-          (drawsContent 1)
         )
       )

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2022-01-23  Matt Woodrow  <mattwoodrow@apple.com>
+
+        Position:fixed layers shouldn't allocate a backing buffer if all children are offscreen.
+        https://bugs.webkit.org/show_bug.cgi?id=235420
+        <rdar://86612099>
+
+        Reviewed by Simon Fraser and Darin Adler.
+
+        Adds a bounds intersection check to isPaintDestinationForDescendantLayers,
+        so that we can exclude descendants that definitely won't draw anything into
+        the compositing layer. Uses a conservative check, which gives up if there are
+        any transforms in the ancestor chain.
+
+        Test: compositing/backing/no-backing-for-offscreen-children-of-position-fixed.html
+
+        * rendering/RenderLayerBacking.cpp:
+        (WebCore::intersectsWithAncestor):
+        (WebCore::RenderLayerBacking::isPaintDestinationForDescendantLayers const):
+
 2022-01-23  Darin Adler  <darin@apple.com>
 

trunk/Source/WebCore/rendering/RenderLayerBacking.cpp

@@ -2791 +2791 @@
 }
 
+static std::optional<bool> intersectsWithAncestor(const RenderLayer& child, const RenderLayer& ancestor, const LayoutRect& ancestorCompositedBounds)
+{
+    // If any layers between child and ancestor are transformed, then adjusting the offset is
+    // insufficient to convert coordinates into ancestor's coordinate space.
+    for (auto* layer = &child; layer != &ancestor; layer = layer->parent()) {
+        if (!layer->canUseOffsetFromAncestor())
+            return std::nullopt;
+    }
+
+    auto offset = child.convertToLayerCoords(&ancestor, { }, RenderLayer::AdjustForColumns);
+    auto overlap = child.overlapBounds();
+    overlap.moveBy(offset);
+    return overlap.intersects(ancestorCompositedBounds);
+}
+
 // Conservative test for having no rendered children.
 bool RenderLayerBacking::isPaintDestinationForDescendantLayers(RenderLayer::PaintedContentRequest& request) const
 {
     bool hasPaintingDescendant = false;
-    traverseVisibleNonCompositedDescendantLayers(m_owningLayer, [&hasPaintingDescendant, &request](const RenderLayer& layer) {
-        hasPaintingDescendant |= layer.isVisuallyNonEmpty(&request);
+    traverseVisibleNonCompositedDescendantLayers(m_owningLayer, [&hasPaintingDescendant, &request, this](const RenderLayer& layer) {
+        RenderLayer::PaintedContentRequest localRequest;
+        if (layer.isVisuallyNonEmpty(&localRequest)) {
+            bool mayIntersect = intersectsWithAncestor(layer, m_owningLayer, compositedBounds()).value_or(true);
+            if (mayIntersect) {
+                hasPaintingDescendant = true;
+                request.setHasPaintedContent();
+            }
+        }
         return (hasPaintingDescendant && request.isSatisfied()) ? LayerTraversal::Stop : LayerTraversal::Continue;
     });