KawaseBlur (and therefore AdvancedBloom) not rendering correctly on WebGPU

[Slakinov]

The WebGL implementation of Kawase Blur seems to be doing the magic trick where a smooth blur effect can be achieved with relatively few iterations, however when switching over to the WebGPU implementation, the obvious 'displaced copies' effect only vanishes at a very high number of iterations, making it just as expensive as the older BloomFilter.

WebGL, AdvancedBloomFilter, blur:16, quality:8

For some reason, WebGPU only appears to have the same blur radius as WebGL when you multiply it by 4, but the bloom is not smooth.

WebGPU, AdvancedBloomFilter, blur:64, quality:8

To get WebGPU looking smooth like the WebGL version, you have to raise the iterations to around 3x that of WebGL, and even then it appears somewhat 'lumpy'.

WebGPU, AdvancedBloomFilter, blur:64, quality:24

What's going on here?

(running on a Macbook Pro M1, haven't tested elsewhere)