Special purpose graphics instructions are provided to facilitate hidden surface elimination. A Z-buffer check instruction performs multiple, simultaneous unsigned-integer (ordinal) comparisons of newly computed distance (Z) values with the contents of a Z-buffer. Distances of points to be drawn are compared with corresponding values in the Z-buffer, and appropriate bits of a pixel mask are then set to designate those pixels for which the points to be drawn are closer (smaller) than the Z-buffer values. Previously calculated bits of the pixel mask are shifted so that consecutive Z-buffer check instructions accumulate their results in the pixel mask register. A pixel store instruction utilizes the pixel mask to update only those pixel locations in a frame buffer which correspond to a point on a newly rendered surface closer than the surface represented by the current pixel value.