Axiom assumes that there are seperate vertex and fragment programs to deal with but GLSL has one program object that represents the active vertex and fragment shader objects during a rendering state. GLSL Vertex and fragment shader objects are compiled seperately and then attached to a program object and then the program object is linked. Since Ogre can only handle one vertex program and one fragment program being active in a pass, the GLSL Link Program Manager does the same. The GLSL Link program manager acts as a state machine and activates a program object based on the active vertex and fragment program. Previously created program objects are stored along with a unique key in a hash_map for quick retrieval the next time the program object is required.