1. A method for calculating pixel values, the method comprising: transforming geometric primitives from a first coordinate space to a second coordinate space; and for each transformed primitive: rendering the transformed primitive to generate at least one first sample value for a pixel; shifting the transformed primitive in the second coordinate space by a respective sub-pixel offset; and rendering the shifted transformed primitive to generate at least one second sample value for the pixel; and combining the first and second sample values to generate a pixel value for the pixel.