Bug 133184 – Subpixel rendering: Non-compositing transforms with subpixel coordinates paint to wrong position.

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

[zalan]

<rdar://problem/16745606>

[zalan]

Created attachment 231893 [details]
Test reduction

[zalan]

With render layer on (2x display)
1. container positioned at (10, 10) 
2. child box with (non-compositing transform) negative top/left: (-0.25, -0.25)
-> painting coordinates (-0.25, -0.25 round-> -0.5, -0.5) -> in absolute coordinates -> (9.5, 9.5)

without render layer
1. container positioned at (10, 10) 
2. child box with negative top/left: (-0.25, -0.25)
-> painting coordinates ((-0.25, -0.25) -> (10 - 0.25, 10 - 0.25) -> (9.75, 9.75)  round-> (10, 10). final painting coords (10, 10)

This happens only on halfway values as the rounding direction is different for negative and positive values. (always away from zero). 

-non halfway values 
container at (10, 10)

child (RenderLayer on): (-0.1, -0.1) round-> (-0, -0) -> in absolute coords (10, 10)
child (RenderLayer off): (-0.1, -0.1) -> (10 - 0.1, 10 - 0.1) -> (9.9, 9.9) round-> (10, 10)

child (RenderLayer on): (-0.3, -0.3) round-> (-0.5, -0.5) -> in absolute coords (9.5, 9.5)
child (RenderLayer off): (-0.3, -0.3) -> (10 - 0.3, 10 - 0.3) -> (9.7, 9.7) round-> (9.5, 9.5)

[zalan]

*** Bug 133241 has been marked as a duplicate of this bug. ***

[zalan]

Created attachment 232002 [details]
Patch

[WebKit Commit Bot]

Attachment 232002 [details] did not pass style-queue:


ERROR: Source/WebCore/platform/LayoutUnit.h:940:  More than one command on the same line  [whitespace/newline] [4]
Total errors found: 1 in 6 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[WebKit Commit Bot]

Comment on attachment 232002 [details]
Patch

Clearing flags on attachment: 232002

Committed r169309: <http://trac.webkit.org/changeset/169309>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.