Efficient shader operation

Abstract

A method of operating a GPU is described wherein input attributes used in executing a first part of a geometry task are fetched 202 by a shader core. The first part of the task executes 204 a first part of a shader to calculate position data for each instance of the task. The first part of the task is executed to output 206 the position data for each instance of the task. The task is then descheduled 210 until cull results are received for each instance. In response to receiving cull results indicating at least one remaining instance in the task, input attributes used in executing a second part of a task are fetched 212. The second part of the task executes 214 a second part of a shader to calculate varyings (attributes of a primitive vertex that varies across the primitive, e.g. texture coordinate or colour) for each remaining instance. The second part of the task is executed and the varyings for each remaining instance are output 216.