Changeset 53173 in webkit

Timestamp:

Jan 12, 2010 6:08:10 PM (14 years ago)

Author:

Simon Fraser

Message:

2010-01-12 Simon Fraser <Simon Fraser>

Reviewed by Dan Bernstein.

position:fixed and transform on same element breaks fixed behavior
​https://bugs.webkit.org/show_bug.cgi?id=31283

Fix interactions of transforms and fixed positioning, namely that fixed position
elements with a transformed ancestor are positioned relative to that ancestor,
and an element with both a transform and fixed position respects that positioning.

Test: transforms/2d/transform-fixed-container.html

• rendering/RenderBox.cpp: (WebCore::RenderBox::mapLocalToContainer): (WebCore::RenderBox::mapAbsoluteToLocalPoint): Transforms should not unconditionally stop the propagation of the 'fixed' flag to ancestors, but only if the transformed element is not itself fixed.

• rendering/RenderLayer.cpp: (WebCore::RenderLayer::convertToLayerCoords): Fix this method to behave correctly for fixed position layers whose container is not the root, but some other (probably transformed) ancestor. In that case, we can fall into the "position: absolute" code path.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/platform/mac/transforms/2d/transform-fixed-container-expected.checksum (added)
• LayoutTests/platform/mac/transforms/2d/transform-fixed-container-expected.png (added)
• LayoutTests/platform/mac/transforms/2d/transform-fixed-container-expected.txt (added)
• LayoutTests/transforms/2d/transform-fixed-container.html (added)
• WebCore/ChangeLog (modified) (1 diff)
• WebCore/rendering/RenderBox.cpp (modified) (3 diffs)
• WebCore/rendering/RenderLayer.cpp (modified) (2 diffs)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2010-01-12  Simon Fraser  <simon.fraser@apple.com>
+
+        Reviewed by Dan Bernstein.
+
+        position:fixed and transform on same element breaks fixed behavior
+        https://bugs.webkit.org/show_bug.cgi?id=31283
+
+        Test for transforms combined with fixed positioning.
+
+        * platform/mac/transforms/2d/transform-fixed-container-expected.checksum: Added.
+        * platform/mac/transforms/2d/transform-fixed-container-expected.png: Added.
+        * platform/mac/transforms/2d/transform-fixed-container-expected.txt: Added.
+        * transforms/2d/transform-fixed-container.html: Added.
+
 2010-01-12  Dumitru Daniliuc  <dumi@chromium.org>
 

trunk/WebCore/ChangeLog

@@ +1 @@
+2010-01-12  Simon Fraser  <simon.fraser@apple.com>
+
+        Reviewed by Dan Bernstein.
+
+        position:fixed and transform on same element breaks fixed behavior
+        https://bugs.webkit.org/show_bug.cgi?id=31283
+
+        Fix interactions of transforms and fixed positioning, namely that fixed position
+        elements with a transformed ancestor are positioned relative to that ancestor,
+        and an element with both a transform and fixed position respects that positioning.
+        
+        Test: transforms/2d/transform-fixed-container.html
+
+        * rendering/RenderBox.cpp:
+        (WebCore::RenderBox::mapLocalToContainer):
+        (WebCore::RenderBox::mapAbsoluteToLocalPoint):
+        Transforms should not unconditionally stop the propagation of the 'fixed' flag to ancestors,
+        but only if the transformed element is not itself fixed.
+        
+        * rendering/RenderLayer.cpp:
+        (WebCore::RenderLayer::convertToLayerCoords):
+        Fix this method to behave correctly for fixed position layers whose container is not
+        the root, but some other (probably transformed) ancestor. In that case, we can fall into
+        the "position: absolute" code path.
+
 2010-01-12  Tony Chang  <tony@chromium.org>
 

trunk/WebCore/rendering/RenderBox.cpp

@@ -942 +942 @@
     }
 
-    if (style()->position() == FixedPosition)
-        fixed = true;
-
     bool containerSkipped;
     RenderObject* o = container(repaintContainer, &containerSkipped);
@@ -950 +947 @@
         return;
 
+    bool isFixedPos = style()->position() == FixedPosition;
     bool hasTransform = hasLayer() && layer()->transform();
-    if (hasTransform)
-        fixed = false;  // Elements with transforms act as a containing block for fixed position descendants
-
+    if (hasTransform) {
+        // If this box has a transform, it acts as a fixed position container for fixed descendants,
+        // and may itself also be fixed position. So propagate 'fixed' up only if this box is fixed position.
+        fixed &= isFixedPos;
+    } else
+        fixed |= isFixedPos;
+    
     IntSize containerOffset = offsetFromContainer(o);
 
@@ -980 +982 @@
     ASSERT(!view() || !view()->layoutStateEnabled());
     
-    if (style()->position() == FixedPosition)
-        fixed = true;
-
+    bool isFixedPos = style()->position() == FixedPosition;
     bool hasTransform = hasLayer() && layer()->transform();
-    if (hasTransform)
-        fixed = false;  // Elements with transforms act as a containing block for fixed position descendants
+    if (hasTransform) {
+        // If this box has a transform, it acts as a fixed position container for fixed descendants,
+        // and may itself also be fixed position. So propagate 'fixed' up only if this box is fixed position.
+        fixed &= isFixedPos;
+    } else
+        fixed |= isFixedPos;
     
     RenderObject* o = container();

trunk/WebCore/rendering/RenderLayer.cpp

@@ -987 +987 @@
     if (ancestorLayer == this)
         return;
-        
-    if (renderer()->style()->position() == FixedPosition) {
-        // Add in the offset of the view.  We can obtain this by calling
+
+    EPosition position = renderer()->style()->position();
+    if (position == FixedPosition && (!ancestorLayer || ancestorLayer == renderer()->view()->layer()) {
+        // If the fixed layer's container is the root, just add in the offset of the view. We can obtain this by calling
         // localToAbsolute() on the RenderView.
         FloatPoint absPos = renderer()->localToAbsolute(FloatPoint(), true);
@@ -998 +999 @@
  
     RenderLayer* parentLayer;
-    if (renderer()->style()->position() == AbsolutePosition) {
-        // Do what enclosingPositionedAncestor() does, but check for ancestorLayer along the way
+    // For a fixed layer, if we're asking for coords relative to some other ancestor, then it must be
+    // enclosed in a fixed position container (e.g. a transformed element), so it behaves like an absolutely
+    // positioned element.
+    if (position == AbsolutePosition || position == FixedPosition) {
+        // Do what enclosingPositionedAncestor() does, but check for ancestorLayer along the way.
         parentLayer = parent();
         bool foundAncestorFirst = false;