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 <e...@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 <zheng...@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 <t...@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 <aba...@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 <zheng...@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 <e...@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 >>>> >> _______________________________________________ >>>> >> webkit-dev mailing list >>>> >> webkit-dev@lists.webkit.org >>>> >> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev >>>> >> >>>> >> >>>> > _______________________________________________ >>>> > webkit-dev mailing list >>>> > webkit-dev@lists.webkit.org >>>> > http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev >>>> > >>>> _______________________________________________ >>>> webkit-dev mailing list >>>> webkit-dev@lists.webkit.org >>>> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev >>> >>> >> _______________________________________________ >> webkit-dev mailing list >> webkit-dev@lists.webkit.org >> http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev >> > _______________________________________________ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev