This is why the XRender extension was introduced. There you have antialiasing, all blending modes you could wish for, subpixel coordinates, advanced drawing operations like gradients and it is fast because it is fully hardware accelerated. All working over a very efficient wire protocol. E.g. Cairo uses Xrender as a backend.
It's not all hardware accelerated though is it. Both the X server and Cairo depend on the pixman library, which is a CPU/SIMD optimized pixel manipulation library.
Even xf86-video-intel, the intel X11 driver package, on my system depends on pixman.
