1. A graphics processing unit comprising: a tiling unit configured to identify a plurality of primitives touching a first tile of a plurality of tiles in an image frame, to determine a representative primitive of the plurality of primitives using a depth value of each of the plurality of primitives, and to determine visible primitives and invisible primitives of the plurality of primitives for the first tile using a depth value of the representative primitive; and a rasterizer configured to rasterize the representative primitive and the visible primitives for the first tile, wherein the representative primitive is rasterized prior to the visible primitives instead of its original rendering order, the invisible primitives are not rasterized, and the visible primitives are rasterized according to their original rendering order, wherein the representative primitive is determined based on its proximity to a camera among the plurality of primitives that touch the first tile, wherein the rasterizer is configured to receive a primitive list for the first tile from memory, and the primitive list includes an identifier of the representative primitive and identifiers of the visible primitives, wherein the rasterizer comprises a sequencer configured to extract the identifier of the representative primitive from the primitive list, and to change the order in which the representative primitive is rasterized by referring to the identifier of the representative primitive.