Changeset 279748 in webkit

Timestamp:

Jul 8, 2021 1:29:32 PM (13 months ago)

Author:

Simon Fraser

Message:

Scrollbar hidden when scroller has a negative z-index child
​https://bugs.webkit.org/show_bug.cgi?id=227545

Reviewed by Alan Bujtas.
Source/WebCore:

The code to ensure that overflow:scroll scrollbars appeared on top of composited descendant
layers had incorrect behavior if the only descendant had negative z-index; it would move the
overflow controls container layer to be after that descendant, and thus behind foreground
content.

Fix by inserting the overflow controls container layer in front of the frontmost of the
descendant and the scroller itself.

Test: compositing/scrolling/async-overflow-scrolling/negative-z-in-scroller-hidden-scrollbar.html

• rendering/RenderLayerCompositor.cpp:

(WebCore::RenderLayerCompositor::adjustOverflowScrollbarContainerLayers):

LayoutTests:

• compositing/scrolling/async-overflow-scrolling/layer-for-negative-z-in-scroller-expected.txt: Rebaseline
• compositing/scrolling/async-overflow-scrolling/negative-z-in-scroller-hidden-scrollbar-expected.html: Added.
• compositing/scrolling/async-overflow-scrolling/negative-z-in-scroller-hidden-scrollbar.html: Added.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/compositing/scrolling/async-overflow-scrolling/layer-for-negative-z-in-scroller-expected.txt (modified) (2 diffs)
• LayoutTests/compositing/scrolling/async-overflow-scrolling/negative-z-in-scroller-hidden-scrollbar-expected.html (added)
• LayoutTests/compositing/scrolling/async-overflow-scrolling/negative-z-in-scroller-hidden-scrollbar.html (added)
• Source/WebCore/ChangeLog (modified) (1 diff)
• Source/WebCore/rendering/RenderLayerCompositor.cpp (modified) (2 diffs)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2021-07-08  Simon Fraser  <simon.fraser@apple.com>
+
+        Scrollbar hidden when scroller has a negative z-index child
+        https://bugs.webkit.org/show_bug.cgi?id=227545
+
+        Reviewed by Alan Bujtas.
+
+        * compositing/scrolling/async-overflow-scrolling/layer-for-negative-z-in-scroller-expected.txt: Rebaseline
+        * compositing/scrolling/async-overflow-scrolling/negative-z-in-scroller-hidden-scrollbar-expected.html: Added.
+        * compositing/scrolling/async-overflow-scrolling/negative-z-in-scroller-hidden-scrollbar.html: Added.
+
 2021-07-08  Yoshiaki Jitsukawa  <yoshiaki.jitsukawa@sony.com>
 

trunk/LayoutTests/compositing/scrolling/async-overflow-scrolling/layer-for-negative-z-in-scroller-expected.txt

@@ -20 +20 @@
                   (bounds 200.00 200.00)
                   (contentsOpaque 1)
-                )
-              )
-            )
-            (GraphicsLayer
-              (position 9.00 9.00)
-              (bounds 300.00 300.00)
-              (clips 1)
-              (children 1
-                (GraphicsLayer
-                  (position 285.00 0.00)
-                  (bounds 15.00 300.00)
-                  (drawsContent 1)
                 )
               )
@@ -59 +47 @@
               )
             )
+            (GraphicsLayer
+              (position 9.00 9.00)
+              (bounds 300.00 300.00)
+              (clips 1)
+              (children 1
+                (GraphicsLayer
+                  (position 285.00 0.00)
+                  (bounds 15.00 300.00)
+                  (drawsContent 1)
+                )
+              )
+            )
           )
         )

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2021-07-08  Simon Fraser  <simon.fraser@apple.com>
+
+        Scrollbar hidden when scroller has a negative z-index child
+        https://bugs.webkit.org/show_bug.cgi?id=227545
+
+        Reviewed by Alan Bujtas.
+        
+        The code to ensure that overflow:scroll scrollbars appeared on top of composited descendant
+        layers had incorrect behavior if the only descendant had negative z-index; it would move the
+        overflow controls container layer to be after that descendant, and thus behind foreground
+        content.
+
+        Fix by inserting the overflow controls container layer in front of the frontmost of the
+        descendant and the scroller itself.
+
+        Test: compositing/scrolling/async-overflow-scrolling/negative-z-in-scroller-hidden-scrollbar.html
+
+        * rendering/RenderLayerCompositor.cpp:
+        (WebCore::RenderLayerCompositor::adjustOverflowScrollbarContainerLayers):
+
 2021-07-08  Yoshiaki Jitsukawa  <yoshiaki.jitsukawa@sony.com>
 

trunk/Source/WebCore/rendering/RenderLayerCompositor.cpp

@@ -1485 +1485 @@
             continue;
 
-        LOG_WITH_STREAM(Compositing, stream << "Moving overflow controls layer for " << overflowScrollingLayer << " to appear after " << lastContainedDescendant);
-
         overflowContainerLayer->removeFromParent();
 
@@ -1500 +1498 @@
 
         auto* lastDescendantGraphicsLayer = lastContainedDescendantBacking->childForSuperlayers();
-        auto lastDescendantIndex = layerChildren.findMatching([&](auto& item) {
-            return item.ptr() == lastDescendantGraphicsLayer;
-        });
-
-        if (lastDescendantIndex != notFound)
-            layerChildren.insert(lastDescendantIndex + 1, *overflowContainerLayer);
+        auto* overflowScrollerGraphicsLayer = overflowBacking->childForSuperlayers();
+        
+        std::optional<size_t> lastDescendantLayerIndex;
+        std::optional<size_t> scrollerLayerIndex;
+        for (size_t i = 0; i < layerChildren.size(); ++i) {
+            const auto* graphicsLayer = layerChildren[i].ptr();
+            if (graphicsLayer == lastDescendantGraphicsLayer)
+                lastDescendantLayerIndex = i;
+            else if (graphicsLayer == overflowScrollerGraphicsLayer)
+                scrollerLayerIndex = i;
+        }
+
+        if (lastDescendantLayerIndex && scrollerLayerIndex) {
+            auto insertionIndex = std::max(lastDescendantLayerIndex.value() + 1, scrollerLayerIndex.value() + 1);
+            LOG_WITH_STREAM(Compositing, stream << "Moving overflow controls layer for " << overflowScrollingLayer << " to appear after " << lastContainedDescendant);
+            layerChildren.insert(insertionIndex, *overflowContainerLayer);
+        }
 
         overflowBacking->adjustOverflowControlsPositionRelativeToAncestor(stackingContextLayer);