Changeset 267067 in webkit

Timestamp:

Sep 14, 2020, 7:17:25 PM (6 years ago)

Author:

Simon Fraser

Message:

REGRESSION (Async overflow scroll): Code snippets on getkirby.com appear and disappear as content is scrolled
​https://bugs.webkit.org/show_bug.cgi?id=216490
<rdar://problem/67018073>

Reviewed by Zalan Bujtas.
Source/WebCore:

The content in question had a z-order layer tree like this:

A (0,0) width=997 height=829 (layerID 20) {sc 2} RenderView

+ B (0,0) width=997 height=8 RenderBlock HTML class='no-js'

+ C (0,0) width=997 height=829 RenderFlexibleBox MAIN

n D (0,0) width=256 height=829 RenderFlexibleBox NAV class='left panel'

n E (0,0) width=256 height=829 (layerID 25) {sc 3} RenderBlock DIV class='scroller'

n F (256,0) width=741 height=829 RenderFlexibleBox ARTICLE class='main panel'

n G (0,0) width=741 height=829 (layerID 26) {sc 4} RenderBlock DIV class='scroller'

n H (0,-816) width=741 height=2810 RenderBlock DIV class='article-content'

+ I (0,0) width=256 height=1000 (layerID 27) overlap RenderBlock (relative positioned) DIV class='content'
+ J (10,300) width=721 height=202 (layerID 28) overlap RenderBlock (relative positioned) DIV class='relative-box'
+ K (10,802) width=721 height=202 (layerID 29) overlap RenderBlock (relative positioned) DIV class='relative-box'
+ L (10,1304) width=721 height=202 (layerID 30) overlap RenderBlock (relative positioned) DIV class='relative-box'
+ M (10,1806) width=721 height=202 (layerID 31) overlap RenderBlock (relative positioned) DIV class='relative-box'
+ M (10,2308) width=721 height=202 (layerID 32) overlap RenderBlock (relative positioned) DIV class='relative-box'

When layer 'G' is scrolled, the code would find the paint-order parent, F, which is normal-flow because it has overflow:hidden,
and would call setDescendantsNeedUpdateBackingAndHierarchyTraversal() on it. However, that doesn't go high enough, because
we need to update J-M since their ancestor clipping stacks have geometry that relies on the scroll position of G. If we don't
update that geometry, GraphicsLayers have an incorrect notion of what's visible, and we don't attach backing store.

The fix is to climb up to the stacking context B and call setDescendantsNeedUpdateBackingAndHierarchyTraversal() on it.

Test: compositing/scrolling/async-overflow-scrolling/nested-scrollers-backing-attachment.html

• rendering/RenderLayer.cpp:

(WebCore::RenderLayer::scrollTo):

LayoutTests:

• compositing/scrolling/async-overflow-scrolling/nested-scrollers-backing-attachment-expected.txt: Added.
• compositing/scrolling/async-overflow-scrolling/nested-scrollers-backing-attachment.html: Added.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/compositing/scrolling/async-overflow-scrolling/clipped-layer-in-overflow-nested-expected.txt (modified) (1 diff)
• LayoutTests/compositing/scrolling/async-overflow-scrolling/nested-scrollers-backing-attachment-expected.txt (added)
• LayoutTests/compositing/scrolling/async-overflow-scrolling/nested-scrollers-backing-attachment.html (added)
• LayoutTests/platform/ios-wk2/compositing/scrolling/async-overflow-scrolling/clipped-layer-in-overflow-nested-expected.txt (modified) (1 diff)
• LayoutTests/platform/ios-wk2/compositing/scrolling/async-overflow-scrolling/nested-scrollers-backing-attachment-expected.txt (added)
• Source/WebCore/ChangeLog (modified) (1 diff)
• Source/WebCore/rendering/RenderLayer.cpp (modified) (1 diff)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2020-09-14  Simon Fraser  <simon.fraser@apple.com>
+
+        REGRESSION (Async overflow scroll): Code snippets on getkirby.com appear and disappear as content is scrolled
+        https://bugs.webkit.org/show_bug.cgi?id=216490
+        <rdar://problem/67018073>
+
+        Reviewed by Zalan Bujtas.
+
+        * compositing/scrolling/async-overflow-scrolling/nested-scrollers-backing-attachment-expected.txt: Added.
+        * compositing/scrolling/async-overflow-scrolling/nested-scrollers-backing-attachment.html: Added.
+
 2020-09-14  Chris Dumez  <cdumez@apple.com>
 

trunk/LayoutTests/compositing/scrolling/async-overflow-scrolling/clipped-layer-in-overflow-nested-expected.txt

@@ -88 +88 @@
                 (GraphicsLayer
                   (position 23.00 23.00)
+                  (bounds origin 0.00 150.00)
                   (bounds 195.00 210.00)
                   (clips 1)

trunk/LayoutTests/platform/ios-wk2/compositing/scrolling/async-overflow-scrolling/clipped-layer-in-overflow-nested-expected.txt

@@ -77 +77 @@
                 (GraphicsLayer
                   (position 23.00 23.00)
+                  (bounds origin 0.00 150.00)
                   (bounds 210.00 210.00)
                   (clips 1)

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2020-09-14  Simon Fraser  <simon.fraser@apple.com>
+
+        REGRESSION (Async overflow scroll): Code snippets on getkirby.com appear and disappear as content is scrolled
+        https://bugs.webkit.org/show_bug.cgi?id=216490
+        <rdar://problem/67018073>
+
+        Reviewed by Zalan Bujtas.
+        
+        The content in question had a z-order layer tree like this:
+
+            A (0,0) width=997 height=829 (layerID 20) {sc 2} RenderView 
+              + B (0,0) width=997 height=8 RenderBlock  HTML  class='no-js'
+                + C (0,0) width=997 height=829 RenderFlexibleBox  MAIN 
+                  n D (0,0) width=256 height=829 RenderFlexibleBox  NAV  class='left panel'
+                    n E (0,0) width=256 height=829 (layerID 25) {sc 3} RenderBlock  DIV  class='scroller'
+                  n F (256,0) width=741 height=829 RenderFlexibleBox  ARTICLE  class='main panel'
+                    n G (0,0) width=741 height=829 (layerID 26) {sc 4} RenderBlock  DIV  class='scroller'
+                      n H (0,-816) width=741 height=2810 RenderBlock  DIV  class='article-content'
+                + I (0,0) width=256 height=1000 (layerID 27) overlap RenderBlock (relative positioned)  DIV  class='content'
+                + J (10,300) width=721 height=202 (layerID 28) overlap RenderBlock (relative positioned)  DIV  class='relative-box'
+                + K (10,802) width=721 height=202 (layerID 29) overlap RenderBlock (relative positioned)  DIV  class='relative-box'
+                + L (10,1304) width=721 height=202 (layerID 30) overlap RenderBlock (relative positioned)  DIV  class='relative-box'
+                + M (10,1806) width=721 height=202 (layerID 31) overlap RenderBlock (relative positioned)  DIV  class='relative-box'
+                + M (10,2308) width=721 height=202 (layerID 32) overlap RenderBlock (relative positioned)  DIV  class='relative-box'
+
+        When layer 'G' is scrolled, the code would find the paint-order parent, F, which is normal-flow because it has overflow:hidden,
+        and would call setDescendantsNeedUpdateBackingAndHierarchyTraversal() on it. However, that doesn't go high enough, because
+        we need to update J-M since their ancestor clipping stacks have geometry that relies on the scroll position of G. If we don't
+        update that geometry, GraphicsLayers have an incorrect notion of what's visible, and we don't attach backing store.
+
+        The fix is to climb up to the stacking context B and call setDescendantsNeedUpdateBackingAndHierarchyTraversal() on it.
+
+        Test: compositing/scrolling/async-overflow-scrolling/nested-scrollers-backing-attachment.html
+
+        * rendering/RenderLayer.cpp:
+        (WebCore::RenderLayer::scrollTo):
+
 2020-09-14  Chris Dumez  <cdumez@apple.com>
 

trunk/Source/WebCore/rendering/RenderLayer.cpp

@@ -2730 +2730 @@
 
                 // Scroll position can affect the location of a composited descendant (which may be a sibling in z-order),
-                // so trigger a descendant walk from the paint-order parent.
-                if (auto* paintParent = paintOrderParent())
+                // so trigger a descendant walk from the stacking context.
+                if (auto* paintParent = stackingContext())
                     paintParent->setDescendantsNeedUpdateBackingAndHierarchyTraversal();
             }