1. A method of combining a first Graphics Processing Unit (GPU) program with a second GPU program, comprising the steps of: evaluating, on a processing unit, each line in the second GPU program, if a line contains a local variable, rename said local variable if its name is the same as the name of another local variable in the first program; if a line contains an explicit texture coordinate reference, eliminate said explicit texture coordinate reference from the executable part of the program, if said explicit texture coordinate reference is dependent upon said first program, and replace said eliminated texture reference with a single pixel reference.