Bug 104294 – Incorrect position of layers for fixed position elements when page is scaled smaller than viewport

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

[Xianzhu Wang]

Created attachment 178072 [details]
test case

This might be for Chromium only. Not tested on other platforms.

scrollOffsetForFixedPosition() calculates incorrect position for fixed elements when the content (originally larger than viewport) is scaled to smaller than the viewport, causing the graphics layers of fixed position elements be placed at wrong positions.

To reproduce, run the attached test case on chromium-linux. The position of the layer for the fixed element is (218, 230). Should be (10, 10).

[Xianzhu Wang]

Created attachment 178080 [details]
Patch

[WebKit Review Bot]

Comment on attachment 178080 [details]
Patch

Attachment 178080 [details] did not pass chromium-ews (chromium-xvfb):
Output: http://queues.webkit.org/results/15170670

[Xianzhu Wang]

Created attachment 178087 [details]
Add missing expected file

[Xianzhu Wang]

Comment on attachment 178087 [details]
Add missing expected file

View in context: https://bugs.webkit.org/attachment.cgi?id=178087&action=review

Added some explanations for reviewers.

> Source/WebCore/page/scrolling/ScrollingCoordinator.cpp:71
> +    if (maxValue <= 0)

If contentsSize < visibleContentSize, return 0 directly.
All other changed code should be equivalent with the original code.

> Source/WebCore/page/scrolling/ScrollingCoordinator.cpp:-94
> -        (contentsSize.height() - visibleContentRect.height() * frameScaleFactor) / maxOffset.height());

The above code is moved into fixedPositionScrollOffset().
Here maxOffset might be 0, and there were unnecessary floating point operations on infinity values.

[Xianzhu Wang]

@bdakin, could you please review this change? Thanks!

[James Robinson]

Comment on attachment 178087 [details]
Add missing expected file

R=me

[WebKit Review Bot]

Comment on attachment 178087 [details]
Add missing expected file

Clearing flags on attachment: 178087

Committed r137368: <http://trac.webkit.org/changeset/137368>

[WebKit Review Bot]

All reviewed patches have been landed.  Closing bug.

[Beth Dakin]

compositing/geometry/fixed-position-composited-page-scale-smaller-than-viewport.html is failing on the WK2 bots.

[Beth Dakin]

(In reply to comment #9)
> compositing/geometry/fixed-position-composited-page-scale-smaller-than-viewport.html is failing on the WK2 bots.

Though it seems fine on my computer. Ugh.