When a renderer of a graphics processor is to perform a graphics rendering operation that uses one or more texture layers in accordance with contribution control data that controls the contribution that each texture layer makes to the rendering operation for a group of fragments, the renderer determines contribution control data for each fragment in the group, and based on the determined contribution control data, either: fetches and uses the texture data values for a texture layer for each fragment in the group from memory, or does not fetch texture data values for a texture layer for each fragment in the group from memory and instead uses a dummy value for the texture layer for each fragment in the group for the graphics rendering operation.