[skottie] Fix motion blur glitches around domain edges
For motion blur we're sampling within some window around a given t.
If t is close to the layer in/out point, things get murky: for samples
which fall outside the layer lifespan, we skip drawing => fewer samples
are accumulated => the opacity of the result drops => visual glitches.
The solution is to modulate the frame alpha based on the number of
*visible* samples, and skip rendering when no samples are visible.
Bug: skia:9486
Change-Id: I8d9692ae1589b43d9e6f728d7b7ac2fbf39153fe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/245363
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
2 files changed