Subpixel rendering: InlineTextBox mistakenly rounds offset value before painting.

[zalan]

see InlineTextBox::paint() -> roundedForPainting(paintOffset, renderer().document().deviceScaleFactor());

[zalan]

paint offset: 0.1px
location: 0.2px;
-> 0.3px -> snapped to 0.5px; (2x displays)
vs.
paint offset: 0.1px -> snapped to 0px;
location: 0.2px;
-> 0.2px -> snapped to 0px;

[zalan]

Created attachment 235948 [details]
Patch

[Simon Fraser (smfr)]

Comment on attachment 235948 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=235948&action=review

> Source/WebCore/ChangeLog:12
> +        However to ensure that text is painted to where we expect it to be painted, we force our
> +        snapping strategy on final coordinates. -for example, CG ceils vertically (in horizontal context)
> +        vs our rounding strategy.

I don't think I understand this sentence.

[zalan]

Created attachment 235949 [details]
Patch

[Build Bot]

Comment on attachment 235949 [details]
Patch

Attachment 235949 [details] did not pass mac-wk2-ews (mac-wk2):
Output: http://webkit-queues.appspot.com/results/4722611997114368

New failing tests:
fast/inline/hidpi-inline-selection-leaves-gap.html

[Build Bot]

Created attachment 235950 [details]
Archive of layout-test-results from webkit-ews-15 for mac-mountainlion-wk2

The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: webkit-ews-15  Port: mac-mountainlion-wk2  Platform: Mac OS X 10.8.5

[Build Bot]

Comment on attachment 235949 [details]
Patch

Attachment 235949 [details] did not pass mac-ews (mac):
Output: http://webkit-queues.appspot.com/results/5102239861440512

New failing tests:
fast/inline/hidpi-inline-selection-leaves-gap.html

[Build Bot]

Created attachment 235951 [details]
Archive of layout-test-results from webkit-ews-06 for mac-mountainlion

The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: webkit-ews-06  Port: mac-mountainlion  Platform: Mac OS X 10.8.5

[Build Bot]

Comment on attachment 235949 [details]
Patch

Attachment 235949 [details] did not pass mac-ews (mac):
Output: http://webkit-queues.appspot.com/results/5895713594540032

New failing tests:
fast/inline/hidpi-inline-selection-leaves-gap.html

[Build Bot]

Created attachment 235952 [details]
Archive of layout-test-results from webkit-ews-08 for mac-mountainlion

The attached test failures were seen while running run-webkit-tests on the mac-ews.
Bot: webkit-ews-08  Port: mac-mountainlion  Platform: Mac OS X 10.8.5

[zalan]

Created attachment 235978 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 235978 [details]
Patch

Clearing flags on attachment: 235978

Committed r172008: <http://trac.webkit.org/changeset/172008>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.