[webkit-dev] Cross-platform fonts for Layout Tests

[Hao Zheng]

Yes, actually in Skia, Chromium/Linux uses a noop gamma implementation
in SkFontHost_gamma_none.cpp; however, if you use a substantial
implementation in SkFontHost_gamma.cpp, there will be much image
mismatch on Chromium/Linux for every font including Ahem. The slight
differences are on font fringe.
And I think if other WebKit is not using Skia at all, there will
surely be even more differences.

As the gamma implementation on Clank is desired, we should not fix
this bug. Just file the bug to record this difference.

On Fri, Jun 3, 2011 at 2:30 AM, Tony Chang <tony at chromium.org> wrote:
> Perhaps, but in practice, it's not enough.  Here's an ahem pixel test that
> is slightly different on Mac and Chromium Linux:
> http://trac.webkit.org/browser/trunk/LayoutTests/platform/mac/fast/block/basic/010-expected.png
> http://trac.webkit.org/browser/trunk/LayoutTests/platform/chromium-linux/fast/block/basic/010-expected.png
>
> Also, I think it would be hard to tell by examining the HTML if a test uses
> another font.  For example, the line height of an empty block might depend
> on the default font that isn't specified (does <pre></pre> render the same
> height on all platforms?).
> On Thu, Jun 2, 2011 at 10:44 AM, Adam Barth <abarth at webkit.org> wrote:
>>
>> I thought the whole point of Ahem was to avoid those problems.
>>
>> Adam
>>
>>
>> On Thu, Jun 2, 2011 at 1:29 AM, Hao Zheng <zhenghao at chromium.org> wrote:
>> > Actually, even the same Ahem font will be rendered differently on
>> > different platform, depending on the font drawing library, the
>> > anti-aliasing algorithm, subpixel, tiny float-point calculation diff
>> > on different arch.
>> >
>> > On Thu, Jun 2, 2011 at 3:30 AM, Eric Seidel <eric at webkit.org> wrote:
>> >> I know that Ahem is safe to use across multiple platforms (the font
>> >> metrics
>> >> will be the same).  Do we know if there are any other fonts for which
>> >> this
>> >> is true?
>> >> I'd like to make the style-bot yell at people when they use pixel tests
>> >> with
>> >> non-safe fonts.  Right now that list would only include ahem.
>> >> -eric
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