[Impeller] disable depth-stencil and MSAA for gaussian and downsample. #165137
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Arguably this is a semantically equivalent change as we weren't using depth/stencil nor do we benefit from the extra MSAA samples (as MSAA only anti aliases geometry and the only geometry here is a fullscreen rect). |
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Using MSAA w/ depth stencil requires extra work on the GPU to track multiple samples and clear the depth/stencil textures.
See also: https://docs.qualcomm.com/bundle/publicresource/topics/80-78185-2/best_practices.html
Its unclear how much this matters, but adreno recommends minimizing bin count and as such minimizing msaa samples. Well, we can fully minimize it by not enabling it. Removing depth stencil was also considered in the past, this should be removed as it requires us to clear, which isn't free.
Its likely this won't have a huge performance impact, but seems like a good best practice.