What's the point of GTK4 and why does it have to be incompatible with GTK3? Is it really worth it to spend so much developer effort across so many projects to migrate them to GTK4?
The biggest changes are to rendering. GTK 1-3 used Cairo to do CPU rendering. It is slow and incapable of modern rendering features. GTK4 makes good use of the GPU with OpenGL (and kinda Vulkan). It has been a huge win for performance improving animations, shaders, multimedia, zero-copy integration with external projects like WebKit, etc.
Yeah, "good use", and also just happens to no longer support subpixel font antialiasing, so good luck if your screen isn't 4K. Which a lot of screens out there aren't. :-(
There was an attempt to have Cairo use OpenGL but it was mostly unsuccessful and abandoned. Even if that worked the paradigms used are very different and would fight performant GPU usage.
