Created attachment 106592 [details] image used by testcase To reproduce: 1. Load the attached test case 2. Zoom the page once You'll see some red appear to the right of the grid.
Created attachment 106593 [details] testcase
Note that the div#inner and the background-image have the same dimensions: 570x18. But after zooming once, document.getElementById('inner').getBoundingClientRect().height is 17.5! I assume this is the source of the bug.
Maybe related to bug 66256?
By "zoom" you mean command+, or gesture zoom?
Cmd-+
I believe the height is rounded down to floor(18 * 1.2) = 21, and the width is 570*1.2 = 684. This allows the image to scale by a factor of 21/18, giving it a width of 665, leaving 19 horizontal pixels showing red.
I suspect the "auto" value for background-size will have similar issues.
<rdar://problem/10218266>
(In reply to comment #7) > I suspect the "auto" value for background-size will have similar issues. Yes - I see a red line below in "containt" & "auto" case.
(In reply to comment #9) > (In reply to comment #7) > > I suspect the "auto" value for background-size will have similar issues. Same for "100%".
I can't reproduce this bug in recent builds.