Method and apparatus for approximating nonlinear functions in a graphics system

A graphics processing circuit for determining at least one parameter value within a graphics primitive comprising:

• a linear interpolator adapted to receive the graphics primitive, wherein the graphics primitive includes vertex values for a parameter at each vertex of the graphics primitive, wherein the linear interpolator determines a first linear interpolation value for the parameter at a first selected pixel within the primitive based on the vertex values;
• a lookup table operably coupled to the linear interpolator, wherein the lookup table includes:
• a first index generation block, wherein the first index generation block determines a first index, a second index, and a first fractional value based on the first linear interpolation value, wherein the first fractional value is based on a difference between the first linear interpolation value and at least one of the first index and the second index;
• a memory block operably coupled to the index generation block, wherein the memory block stores a discrete sampling of a nonlinear function corresponding to the parameter, wherein the first index and the second index correspond to sample points of the nonlinear function, wherein the memory block provides a first sample of the nonlinear function in response to the first index and a second sample of the nonlinear function in response to the second index;
• and
• a first arithmetic unit operably coupled to the memory block and the first index generation block, wherein the first arithmetic unit generates a first value for the parameter at the first selected pixel based on the first sample, the second sample, and the first fractional value.

A method for determining a nonlinear interpolation value for a parameter at a location within a graphics primitive, comprising:

• receiving a linear interpolation value for the parameter at the location within the graphics primitive;
• determining a first index, a second index, and a fractional value based on the linear interpolation value, wherein the fractional value determines the difference between the linear interpolation value and the first index and the second index;
• applying the first index and the second index to a lookup table to produce a first nonlinear parameter value and a second nonlinear parameter value, wherein the lookup table stores a nonlinear parameter function;
• combining the first nonlinear parameter value, the second nonlinear parameter value and the fraction to produce the nonlinear interpolation value for the parameter at the location.