Blending colors of source and destination primitives by a graphics processing unit is disclosed. The graphics processing unit executes a blending program that blends the primitives. The graphics processing unit receives the blending program from a central processing unit or a graphics application program. For example, the graphics processing unit draws a source primitive in a source texture map and a destination primitive in a destination texture map. The blending program (e.g., a pixel shader) is set to be applied to the primitives, and the graphics processing unit applies the blend mode to each pixel of the primitives, rendering a composite primitive in a destination render target.