[Webkit-unassigned] [Bug 147826] [Cairo] Improve image quality when using newer versions of cairo/pixman

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=147826

--- Comment #5 from Carlos Garcia Campos <cgarcia at igalia.com> ---
(In reply to comment #4)
> This seems like a reasonable change, though I have some concerns about the
> performance implications. It'd probably best to match the Mac port as
> closely as possible here.

I don't think there's much difference in terms of performance, GOOD only uses the box filter for downscaling, otherwise it does bilinear, so in most of the cases it will be the same, and the performance of the box filter is not that different to bilinear either. The difference will be when using BEST, because the Catmull-Rom filter will be definitely slower than bilinear, but it's only used for the High quality interpolation that is supposed to be used when the performance is not that important. WebCore already uses no interpolation (FAST which is NEAREST) when loading or scrolling, and after a timeout of staying in the same position, a better interpolation is used. I don't know exactly the details, though.

And regarding matching Mac, well, it's very difficult to match the performance of two different rendering libraries, in my opinion. But reading the documentation of CGInterpolationQuality this patch matches the definitions of the Medium and High values, I would say:

kCGInterpolationMedium: A medium level of interpolation quality. This setting is slower than the low setting but faster than the high setting.

kCGInterpolationHigh: A high level of interpolation quality. This setting may slow down image rendering.

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