[Webkit-unassigned] [Bug 100551] turn off text antialiasing by default for Chromium Mac, Linux DRT

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=100551





--- Comment #14 from Nico Weber <thakis at chromium.org>  2013-03-13 14:37:58 PST ---
(In reply to comment #13)
> (In reply to comment #12)
> > Turns out skia does turn off lcd antialiasing in SkFontHost_mac_coretext if layout test mode is set, see https://codereview.chromium.org/12316132 and https://bugs.webkit.org/show_bug.cgi?id=110890
> > 
> > So at least on Mac, we probably don't want to do this (since skia already does it). This might be true on linux too.
> > 
> > Text pixel baselines on mac seem to match on 10.6, .7, and .8.
> 
> We get different behavior on Mountain Lion if the test sets -webkit-font-smoothing: none.  We've seen on some tests the edges of Ahem glyphs look different.

In third_party/skia/src/ports/SkFontHost_mac.cpp: Offscreen::getCG(), the parameter generateA8FromLCD
 is effectively set in layout test mode. The function has this test:

    // FIXME: lcd smoothed un-hinted rasterization unsupported.
    if (!generateA8FromLCD && SkMask::kA8_Format == glyph.fMaskFormat) {
        doLCD = false;
        doAA = true;
    }

So skia's stuff only works for A8 pixels. -webkit-font-smoothing probably switches glyphs to something else.

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