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

[Hao Zheng]

For example:
fast/borders/borderRadiusArcs01.html
svg/W3C-SVG-1.1-SE/pservers-pattern-04-f.svg
fast/backgrounds/body-generated-image-propagated-to-root.html

Hundreds of tests with skia drawing are affected by this bug, e.g.
svg-tests, round-corner, gradient, etc.


On Tue, Jun 7, 2011 at 11:58 PM, Dirk Pranke <dpranke at chromium.org> wrote:
> Reftests?
>
> -- Dirk
>
> On Mon, Jun 6, 2011 at 11:00 PM, Hao Zheng <zhenghao at chromium.org> wrote:
>> Unfortunately, even for SVG or images, different drawing
>> implementations will lead to different pixel results. Like this Skia
>> bug, http://code.google.com/p/skia/issues/detail?id=179 , which caused
>> most pages using SkFixed calculation, e.g. round-corner, gradient,
>> svg, etc., produce different rendered image on different platforms. So
>> I think there are many subtle, if possible, issues to make pixels
>> consistent across all platforms.
>>
>> On Tue, Jun 7, 2011 at 1:23 PM, Eric Seidel <eric at webkit.org> wrote:
>>> So are we saying it's impossible to have matching results across all
>>> platforms if a test involves any text (in any font)?
>>>
>>> I know it's certainly possible to have pixel-results for tests which
>>> do not involve text match across all platforms (like SVG or images or
>>> css styling, etc.)
>>>
>>> Or is all this just theory?
>>>
>>> -eric
>>>
>>> On Mon, Jun 6, 2011 at 8:09 PM, Hao Zheng <zhenghao at chromium.org> wrote:
>>>> 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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>>>>>> >> webkit-dev at lists.webkit.org
>>>>>> >> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
>>>>>> >>
>>>>>> >>
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