[Qt] Enable sub-pixel layout

[Allan Sandfeld Jensen]

This is meta bug for tracking enabling sub-pixel layout on the Qt platform.

[Allan Sandfeld Jensen]

I have been experimenting with SUBPIXEL_LAYOUT in order to determine if we should enable it for Qt 5.1 while we are already causing baseline changes due to font rendering.

There does however seem to be a few regression. In particular the text underline seems to get placed a pixel to high. I suggest tracking the progress Mac is having in fixing the regressions in subpixel layout, though we could also bite the bullet and share the experience with them.

Open Mac bugs related to enabling subpixel_layout: bug 101220, bug 111280, bug 112227 and bug 101848.

[Allan Sandfeld Jensen]

Created attachment 194855 [details]
Subpixel underline

An example of the most visible subpixel layout regression. Note the underline under the bug nummer is touching the text, and that the underline under | is intersecting the line instead of going under it.

[Allan Sandfeld Jensen]

Created attachment 194869 [details]
Patch

[Allan Sandfeld Jensen]

(In reply to comment #2)
> Created an attachment (id=194855) [details]
> Subpixel underline
> 
> An example of the most visible subpixel layout regression. Note the underline under the bug nummer is touching the text, and that the underline under | is intersecting the line instead of going under it.

Turned out to be unrelated to the otherwise similar Mac problem. We were just rounding poorly in GraphicsContext::drawLine.

[Early Warning System Bot]

Comment on attachment 194869 [details]
Patch

Attachment 194869 [details] did not pass qt-ews (qt):
Output: http://webkit-commit-queue.appspot.com/results/17321042

[Early Warning System Bot]

Comment on attachment 194869 [details]
Patch

Attachment 194869 [details] did not pass qt-wk2-ews (qt):
Output: http://webkit-commit-queue.appspot.com/results/17297292

[Allan Sandfeld Jensen]

Created attachment 194873 [details]
Patch

Fix wrong comment style

[Allan Sandfeld Jensen]

Created attachment 195071 [details]
Patch

Now only with the enabling part.

[Allan Sandfeld Jensen]

I have run all enabled layout tests after rebaselining for 5.1 before subpixel_layout. It "only" affects around 1000 baselines. I have checked all that had an image-diff of more than 2% and they were all still correct.

[Allan Sandfeld Jensen]

Created attachment 196605 [details]
Patch

[Jocelyn Turcotte]

Comment on attachment 196605 [details]
Patch

r=me, please just make sure to synchronize with Adam and Zoltan to land it.

[Allan Sandfeld Jensen]

Comment on attachment 196605 [details]
Patch

Clearing flags on attachment: 196605

Committed r148594: <http://trac.webkit.org/changeset/148594>

[Allan Sandfeld Jensen]

All reviewed patches have been landed.  Closing bug.