feMorphology is not rendered correctly on Retina display

[Said Abou-Hallawa]

Created attachment 258111 [details]
test case

Open the attached test case which contains an text SVG element with feMorphology filter on Retina display.

Result: The display is corrupted.
Note: If the same test case is opened on non-Retina display, the text is displayed fine.

[Said Abou-Hallawa]

<rdar://problem/22098031>

[Said Abou-Hallawa]

Created attachment 258224 [details]
Patch

[Said Abou-Hallawa]

Created attachment 258254 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 258254 [details]
Patch

Clearing flags on attachment: 258254

Committed r188271: <http://trac.webkit.org/changeset/188271>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[zalan]

Comment on attachment 258254 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=258254&action=review

> Source/WebCore/platform/graphics/filters/FEMorphology.cpp:244
> +    paintingData.width = ceilf(effectDrawingRect.width() * filter.filterScale());
> +    paintingData.height = ceilf(effectDrawingRect.height() * filter.filterScale());
> +    paintingData.radiusX = ceilf(radiusX * filter.filterScale());
> +    paintingData.radiusY = ceilf(radiusY * filter.filterScale());

Why are we ceiling both the location and the dimension here?

[Said Abou-Hallawa]

(In reply to comment #6)
> Comment on attachment 258254 [details]
> Patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=258254&action=review
> 
> > Source/WebCore/platform/graphics/filters/FEMorphology.cpp:244
> > +    paintingData.width = ceilf(effectDrawingRect.width() * filter.filterScale());
> > +    paintingData.height = ceilf(effectDrawingRect.height() * filter.filterScale());
> > +    paintingData.radiusX = ceilf(radiusX * filter.filterScale());
> > +    paintingData.radiusY = ceilf(radiusY * filter.filterScale());
> 
> Why are we ceiling both the location and the dimension here?

Is it wrong to do ceiling here?

The filterScale() is set only to renderer().frame().page()->deviceScaleFactor() which is float. But it is 2 on Retina and 1 on none Retina. Can it be for example 1.5?  I do not know. So I assumed filterScale() is just a float and can be any value.

Now I have floating point calculations even the variables before scaling and after scaling are all integers. I thought it is safer to do ceiling to avoid not setting the bits of the last row or the last column if filterScale() has a fraction. And since we are dealing with a memory bitmap, we are sure that nothing will be drawn outside the image pre allocated area.