When a texture mapper in a graphics processor is to perform a texturing operation for a set of plural execution threads together, the texture mapper determines whether the texturing operation for the set of plural threads can be performed together with the texturing operation for another set of plural execution threads for which a texturing operation is required. When the texture mapper determines that the texturing operations for the sets of plural execution threads can be performed together, it performs the texturing operations for the sets of plural threads together, but when it determines that the texturing operation for the set of plural threads cannot be performed together with the texturing operation for another set of plural execution threads, it performs the texturing operation for the set of plural execution threads alone.