1. A method for tessellation in a tile-based graphics rendering pipeline by a graphics processor, the method comprising: generating an input visibility stream for each tile of a frame, the input visibility stream indicating whether or not an input primitive is visible in each tile when rendered; and generating an output visibility stream for each tile of the frame, the output visibility stream indicating whether or not an output primitive is visible in each tile when rendered, wherein the output primitive is produced by tessellating the input primitive.