1. A region-based deferred 3-D graphics renderer, comprising: a tiling unit configured to input object data describing positions of objects that may be visible in an image to be rendered, the image comprising a plurality of pixels, grouped into tiles, and to calculate, for each object, a respective set of tiles overlapped by that object, and to write identifying data for the object into a display list associated with one or more tiles of the set of tiles, located in a memory, in association with depth information for the object; and an Image Synthesis Processor (ISP) fetch unit coupled to the memory and configured for reading the identifying data and the depth information for objects identified in the display list, and for receiving a depth range produced from depth information for a set of objects presently rendered for the one or more tiles associated with the display list, by an image synthesis processor, and to determine, for objects identified by the identifying data in the display list, whether parameter data for those objects should be fetched and provided to the image synthesis processor for rendering, wherein the image synthesis processor is configured to update the depth range as further objects are rendered for the one or more tiles associated with the display list.