A data processing system comprises a host processor and a graphics processor that renders frames to be output and writes those frames to a frame buffer.When a new frame is to be generated and written to the frame buffer, the host processor determines, for a set of plural sub-regions that the frame has been divided into, which of those sub-regions could have changed from the frame previously used for the frame buffer 30 and generates information indicating which sub-regions should be rendered to generate the new frame on the basis of the determination 31. The information indicating which sub-regions should be rendered to generate the frame is provided to the graphics processor 32 and the graphics processor uses the provided sub-region information to render only the indicated sub-regions 33.