Warnock's Algorithm:

An interesting approach to the hidden-surface problem was presented by Warnock. His method does not try to decide exactly what is happening in the scene but rather just tries to get the display right. Since the resolution of the display increases, the amount of work which the algorithm should do to get the scene right also enhance, (it is also true for scan-line algorithms). The algorithm divides the screen up in sample areas. In some sample areas it shall be easy to decide what to do. If there are no faces in the area, then this is left blank. If the nearest polygon completely covers it, then it may be filled in with the colour of that polygon. If neither of these conditions holds, then the algorithm subdivides the sample area into smaller sample areas & considers each of them in turn. This procedure is repeated as needed. It stops while the sample area satisfies one of the two simple cases or while the sample area is only a single pixel (which may be given the colour of the foremost polygon). The process may also be allowed to continue to half or quarter pixel-sized sample areas, whose colour may be average over a pixel to provide ant aliasing.

The test for whether a polygon surrounds or is disjoint from the sample area is much like a clipping test to see if the polygon sides cross the sample-area boundaries. In fact the minimax test may be employed to identify several of the disjoint polygons. A simple test for whether a polygon is in front of another is a comparison of the z coordinates of the polygon planes at the corners of the sample area.

At each of subdivision, information learned in the previous test may be utilized to simplify the problem. Polygons which are disjoint from the tested sample area shall also be disjoint from all of the sub-areas and do not need further testing. Likewise, a polygon which surrounds the sample area will also surround the sub-areas.