[Webkit-unassigned] [Bug 108929] Text shadow sometimes clipped unexpectedly

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Thu May 12 12:17:30 PDT 2016


Myles C. Maxfield <mmaxfield at apple.com> changed:

           What    |Removed                     |Added
             Status|NEW                         |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #18 from Myles C. Maxfield <mmaxfield at apple.com> ---
This is because of a mismatch between CoreGraphics and CSS. In particular, CoreGraphics doesn't support drawing multiple shadows on text.

We work around that by drawing the text multiple times, one for each shadow. However, we want to make sure that the original text isn't also drawn multiple times, so we bump up the shadow offsets so the text and the shadow don't intersect, and then we clip out the original text (so only the shadow remains).

Unfortunately, this clipping requires knowing where the visual extent of the text is, which WebKit currently has trouble with. In particular, we often use layout extents in lieu of visual extents, which is a problem when the glyphs draw outside of their layout boxes. In this case, it causes us to think the text shadow is much smaller than it really is, so our clipping operation clips to an area which is too small.

A quick and dirty hack would be to inflate this clip rect by an arbitrary amount (and bump up the shadow offset accordingly). However, that doesn't actually solve the problem; it just makes the problem occur less often. The real solution is for WebKit to be properly educated about the difference between layout extents and visual extents, which is a fairly large task.

Therefore, I'd like to mark this as a dup of (an extremely old) bug 6274.

*** This bug has been marked as a duplicate of bug 6274 ***

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