1. A method of determining if a first node in a graph may be combined with a second node in said graph, the method comprising the steps of Determining whether the output buffer of said first node will comprise data that is similar to the input texture of said second node, Examining each program line in said second node to determine if it negates the possibility of combining nodes, and Editing program code to replace any first-node-texture references with a single pixel, where a first-node-texture reference is a reference in the second node's code to a texture that would have been created by the first node.