PRECISE GRADIENT CALCULATION SYSTEM AND METHOD FOR A TEXTURE MAPPING SYSTEM OF A COMPUTER GRAPHICS SYSTEM

A gradient calculation system efficiently calculates precise gradients for planar surfaces of primitives in computer graphics systems using exact closed form solutions. The system is particularly suited for calculating gradients to enable selection of an appropriate texture map resolution in a texture mapping system. In architecture, the gradient calculation system can be implemented in software, hardware, or a combination thereof, and is more particularly implemented as follows. A texture mapping system is provided with a plurality of MIP maps with different texel resolutions. A gradient calculation system associated with the texture mapping system computes texel gradients relative to a pixel of a primitive using closed form equations that result in exact gradients. MIP map selection logic associated with the texture mapping system selects an appropriate MIP map for the pixel from the plurality of MIP maps based upon the calculated exact gradients. Optionally, the system may further include a performance optimization feature for assigning the appropriate MIP map to subsequent pixels of, preferably, the entire primitive, or secondarily, to subsequent pixels of a span of the primitive, when certain gradient criteria are met.