I'm not sure the author is even using the GPU? As I understand it, they are using their own cross platform code to draw into a bitmap, and displaying that bitma

I'm not sure the author is even using the GPU? As I understand it, they are using their own cross platform code to draw into a bitmap, and displaying that bitmap in a view is slow because of all the compositing and color management macOS is doing. It sounds like they are doing all their drawing on the CPU, and using APIs optimized for accuracy; instead of drawing on the GPU using APIs optimized for speed.