When processing a primitive when generating a render output in a graphics processor, the vertices for the primitive are loaded by a vertex loader, but before a primitive setup stage generates per-primitive data for the primitive using the loaded vertices for the primitive, an early culling test is performed for the primitive using data of the loaded vertices for the primitive. When the primitive passes the early culling test, the primitive is sent onwards to the primitive setup stage and to a rasteriser for rasterising the primitive, but when the primitive fails the early culling test, it is discarded from further processing at the early culling test.