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Issue 708784 link

Starred by 1 user
Status: Duplicate
Owner: ----
Closed: Apr 2017
Cc:
e...@chromium.org
drott@chromium.org
vmp...@chromium.org
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Pri: 3
Type: Bug

Blocking:
issue 707807



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Rounding of font ascent and descent may cause wrong visual overflow

Project Member Reported by wangxianzhu@chromium.org, Apr 5 2017 
This might one reason of 707807.

In SimpleFontData.cpp, we round ascent and descent to integer values. If the value is rounded down, the visual overflow of inline boxes may be inadequate to cover all visual overflows of glyphs.

This might require us to inflate the inline box visual overflow rect by 1px to ensure it to cover all overflows.

Comment 1 by wangxianzhu@chromium.org, Apr 5 2017 

I just tried https://codereview.chromium.org/2797293003 which always enables subpixel ascent/descent, and it seemed to fix bug 706298 without inflating visual overflow rects. Do you know what prevents us from always using subpixel ascent/descent? I'm sure rounding ascent/descent will cause inadequate visual overflow rects. If we can't always enable subpixel ascent/descent, would inflating visual overflow rect the only way to avoid paint invalidation issues?

Comment 2 by wangxianzhu@chromium.org, Apr 6 2017

Mergedinto: 706298
Status: Duplicate (was: Available)
After some experiments, I believe this is the cause of bug 706298.
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