alt Hacker NewsThe issue is not performance the issue is that pixel precise operations are difficult on the GPU using graphics features such as shaders.
You don't normally work with pixels but you work with polygonal geometry (triangles) and the GPU does the pixel (fragment) rasterization.
Surely you could at least draw arbitrary rectilinear polygons and expect that they're going to be pixel perfect? After all the GPU is routinely used for compositing rectangular surfaces (desktop windows) with pixel-perfect results.