Improve performance

[Dev-McDuck]

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Describe The Feature Request Below

I understand that it is not paid, but if it were, I would like it to be optimized since it causes too much lag not only when working with many layers but also when baking them, it even crashes the program.

[ucupumar]

Yeah, ucupaint can feel slow sometimes, especially with many layers.

From my findings, most of the issues come from the ucupaint UI itself. I already did some optimization in the latest master branch, but it can be improved much further. I just don't have time to do it yet since I still need to focus on the version 2.4 release, which will happen soon. I'll continue the performance optimization again after version 2.4.0 already been released.