Changeset 187001 in webkit

Timestamp:

Jul 18, 2015 4:54:32 PM (9 years ago)

Author:

Simon Fraser

Message:

Scroll position jumps when scrolling scaling pages down in split view
​https://bugs.webkit.org/show_bug.cgi?id=147072
rdar://problem/21769577

Reviewed by Sam Weinig.

When apple.com/music is in Split View at a reduced scale, scrolling the page
can cause unwanted scroll jumps. This happened because we'd enter
TiledCoreAnimationDrawingArea::scaleViewToFitDocumentIfNeeded() with a pending
layout, so run the autosizing logic. When scrolled near the bottom, the unconstrained
layout resulted in a shorter document, which truncated the scroll position. The
scaled layout then restored the longer document, but it also restored that
truncated scroll position.

Forcing a layout is sufficient to fix the bug for this page, and doing a single
layout (which will happen anyway) is preferable to running the autosize logic
if layout happens to be dirty.

I was not able to make a test to reproduce the problem. Entering
scaleViewToFitDocumentIfNeeded() with pending layout was triggerable
using a transform transition, but I was not able to reproduce incorrect
scroll position restoration.

• WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.mm:

(WebKit::TiledCoreAnimationDrawingArea::scaleViewToFitDocumentIfNeeded):

Location:

trunk/Source/WebKit2

Files:

• ChangeLog (modified) (1 diff)
• WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.mm (modified) (1 diff)

trunk/Source/WebKit2/ChangeLog

@@ +1 @@
+2015-07-18  Simon Fraser  <simon.fraser@apple.com>
+
+        Scroll position jumps when scrolling scaling pages down in split view
+        https://bugs.webkit.org/show_bug.cgi?id=147072
+        rdar://problem/21769577
+
+        Reviewed by Sam Weinig.
+        
+        When apple.com/music is in Split View at a reduced scale, scrolling the page
+        can cause unwanted scroll jumps. This happened because we'd enter
+        TiledCoreAnimationDrawingArea::scaleViewToFitDocumentIfNeeded() with a pending
+        layout, so run the autosizing logic. When scrolled near the bottom, the unconstrained
+        layout resulted in a shorter document, which truncated the scroll position. The
+        scaled layout then restored the longer document, but it also restored that
+        truncated scroll position.
+        
+        Forcing a layout is sufficient to fix the bug for this page, and doing a single
+        layout (which will happen anyway) is preferable to running the autosize logic
+        if layout happens to be dirty.
+
+        I was not able to make a test to reproduce the problem. Entering
+        scaleViewToFitDocumentIfNeeded() with pending layout was triggerable
+        using a transform transition, but I was not able to reproduce incorrect
+        scroll position restoration.
+
+        * WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.mm:
+        (WebKit::TiledCoreAnimationDrawingArea::scaleViewToFitDocumentIfNeeded):
+
 2015-07-17  Andy Estes  <aestes@apple.com>
 

trunk/Source/WebKit2/WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.mm

@@ -281 +281 @@
         return;
 
+    m_webPage.layoutIfNeeded();
+
     int viewWidth = m_webPage.size().width();
     bool documentWidthChangedOrInvalidated = m_webPage.mainFrame()->view()->needsLayout() || (m_lastDocumentSizeForScaleToFit.width() != m_webPage.mainFrameView()->renderView()->unscaledDocumentRect().width());