A display controller provides an output frame to a display for display by sending respective output surface regions that together form the output frame, each respective region of the output surface being generated from a respective region or regions of one or more input surfaces, to the display. When a new version of an output surface region is generated, the display controller determines whether the output surface region has been unchanged for a period, and if it has, then stores the generated output surface region in a frame buffer. Then, for the subsequent frame, checks are performed to see if the output surface region could have changed. If there is no change the stored version of the output surface region is reused, but if there is a change in the output surface region, the output surface region is regenerated.