Horizon split ambient occlusion

A GPU for computing ambient occlusion illumination for a scene, comprising:

• a set-up unit for receiving a group of primitives from a graphics application and generating edge descriptions for the primitives;
• a rasterizer unit coupled to the setup unit for receiving the edge descriptions and rasterizing the primitives into pixel parameters of pixels of a display, wherein the parameters include pixel depth values and pixel normal vectors;
• a shader unit coupled to receive the pixel parameters and perform a shader operations on the pixels, wherein the shader unit performs an ambient occlusion process for each pixel of the display by:
• based on the pixel depth values and a projection matrix used to render the scene, computing a 3-D eye space position for a surface point corresponding to the pixel;
• based on the pixel eye space position, the pixel normal vector, and the depth values, computing horizon heights in relation to the point;
• based on the horizon heights, computing an occlusion term for the pixel;
• based on the pixel eye space position, the pixel normal vector, the depth values and the horizon heights, computing a normal occlusion term for the point;
• and
• computing an ambient occlusion illumination value by combining the horizon occlusion term and the normal occlusion term.

A computer system for computing ambient occlusion illumination for a scene, comprising:

• a processor coupled to a bus and a memory coupled to the bus, the memory having instructions stored there in that when executed by the processor implement a method for for computing ambient occlusion illumination;
• a GPU having a set-up unit for receiving a group of primitives from a graphics application and generating edge descriptions for the primitives and a rasterizer unit coupled to the setup unit for receiving the edge descriptions and rasterizing the primitives into pixel parameters of pixels of a display, wherein the parameters include pixel depth values and pixel normal vectors;
• wherein the shader unit is coupled to receive the pixel parameters and perform a shader operations on the pixels, and wherein the shader unit performs an ambient occlusion process for each pixel of the display by:
• based on the pixel depth values and a projection matrix used to render the scene, computing a 3-D eye space position for a surface point corresponding to the pixel;
• based on the pixel eye space position, the pixel normal vector, and the depth values, computing horizon heights in relation to the point;
• based on the horizon heights, computing an occlusion term for the pixel;
• based on the pixel eye space position, the pixel normal vector, the depth values and the horizon heights, computing a normal occlusion term for the point;
• and
• computing an ambient occlusion illumination value by combining the horizon occlusion term and the normal occlusion term.