Pixelated image when using SkShader, SkRuntimeImageFilter and canvas scaling

[Robert Icusca]

I'm drawing a image as a fill for a shape by converting the SkImage to an SkShader, using also a transform matrix so it can fit within the shape. I also apply some scale to the canvas and everything looks good. 

When I add a SkImageFilters::RuntimeShader image filter I get a pixelated image, even if the shader used shouldn't change anything. Please see: https://fiddle.skia.org/c/587e2eb957c7c5940ed8cbfc297b32fd

Something similar I get when using SkMatrixImageFilter: https://fiddle.skia.org/c/af553c062f412fd7616a96754e89bb96

Is this the expected result ? Is there any general recommendation about how  RuntimeShader  should be used ? I understand the issue can be avoided by not scaling the canvas or the shader but I would try to avoid going down this path. 

Other filters like Blur, Tile work as I expected.

[William Candillon]

This is also our experience and we recommend our users to use super sampling: https://github.com/Shopify/react-native-skia/pull/1737/files#diff-33c9176aadc57001d710fe5597023caca0be18583471be7e878b0e7e0cfb67a5R55

I would also be curious to understand the reasoning of why this is necessary.

Kind regards,

William

[John Stiles]

I found a known bug which might explain this: https://g-issues.skia.org/issues/40044507

(Source: https://source.chromium.org/chromium/chromium/src/+/main:third_party/skia/src/effects/imagefilters/SkRuntimeImageFilter.cpp;l=69-72;drc=18cf818e044f90466b59c4d82d37cb4001eacc71)

It seems like the workaround is to avoid transformations other than basic X/Y translation when using the runtime shader image filter.

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[William Candillon]

Thank you for providing this context, this helps us to document the behaviour to our users.

Kind regards,

William

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