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

[Dirk Pranke]

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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>>>>> >>
>>>>> >>
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>>>>
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