I'm getting bad GPU times 20ms+ on an nvidia GPU with a 4k screen on https://ultralig.ht/ especially towards the top of the page where a lot of time is spent on blend, mix-blend and image shaders and target init.

I looked a bit at a GPU capture of this and identified the offender: it's a full-screen image that is:

1. drawn into a render target as is
2. applied a grayscale filter
3. read back (as a source of mix-blend)
4. applied in mix-blend

So in total we shove it around about 4 times, consuming GPU cycles and memory. It's not clear to me yet what can be done to address this, should discuss at All Hands. One small idea is to optimize a case where the backdrop is a solid color, which appears to be the case here.

Other than this, I don't think the page shows any other abnormalities in terms of GPU usage.

I see sub-1ms GPU times at 4k on a low-end AMD GPU now. There's been lots of work to make mix-blend faster and cacheable.