tree 6cdf7a4c5c2586b7a55e3e1bec6c08743aa302f4
parent 9c1b6c98f7f0b3b911b150feb7157a568b055bb6
author gaaclarke <30870216+gaaclarke@users.noreply.github.com> 1707179564 -0800
committer GitHub <noreply@github.com> 1707179564 -0800
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[Impeller] blur: hold on to 1/8 downsample until the kernel overflows (#50363)

issue: https://github.com/flutter/flutter/issues/142753

After https://github.com/flutter/engine/pull/50262 there were still some
sigmas that could show shimmering around the sigma [50, 100] range which
had a downsample amount of 1/16. This makes those ranges hang on to 1/8
for as long as possible. I'm unable to see any shimmering with
`AiksTest.GaussianBlurAnimatedBackdrop` after this PR. I've also
expanded that test so the clip region could be scaled to make sure that
there aren't sizes which cause it to reappear.

Testing: Expanded on manual testing. Since the error only manifests when
evaluating multiple frames of rendering we don't have infrastructure to
test that.

Here is the graph of `GaussianBlurFilterContents::CalculateScale` after
this change:

<img width="903" alt="Screenshot 2024-02-05 at 2 10 41 PM"
src="https://github.com/flutter/engine/assets/30870216/ac3b735a-95f0-4d7b-af12-58e1ae75278e">

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Objective-C, Java style guides].
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above.
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adding, or the PR is [test-exempt]. See [testing the engine] for
instructions on writing and running engine tests.
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