I love Krita, and have recently taken to painting much of Bob Ross's stuff with it to learn... painting. But I do wish I had time to fix the performance issues. It destroys my surface book I paint with.
Yeah I've gone through that a bunch and it did help, but it seems to be mostly "slow brushes"... but like every brush is slow. The work to add AVX support on the brushes helped those brushes, but not nearly enough. And even fast brushes are perceptually laggy.
Really Krita would benefit massively from brushes being implemented on GPU but the developers (rightly) are worried about the massive complexity gain.
