Anisotropic texture filtering with texture data prefetching
View Patent ↗A circuit arrangement and method utilize texture data prefetching to prefetch texture data used by an anisotropic filtering algorithm. In particular, stride-based prefetching may be used to prefetch texture data for use in anisotropic filtering, where the value of the stride, or difference between successive accesses, is based upon a distance in a memory address space between sample points taken along the line of anisotropy used in an anisotropic filtering algorithm.
1. A method of performing anisotropic texture filtering using a texture defined in a texel coordinate system having u and v axes and a scene defined in a pixel coordinate system having x and y axes, the method comprising, for an initial sample point in the texture at u,v coordinates:
determining a line of anisotropy, including determining au, av values for the line of anisotropy as follows:
au =max( du/dx, du/dy )
av =max( dv/dx, dv/dy )
where du/dx is a ratio between texel coordinates along the u axis and pixel coordinates along the x axis, du/dy is a ratio between texel coordinates along the u axis and pixel coordinates along the y axis, dv/dx is a ratio between texel coordinates along the v axis and pixel coordinates along the x axis, and dv/dy is a ratio between texel coordinates along the v axis and pixel coordinates along the y axis;
determining n sample points along the line of anisotropy, including determining ui, vi coordinates for each sample point i, where i=0 to n−1, as follows:
ui=u +( i*au /( n− 1)− au/ 2)
vi=v +( i*av /( n− 1)− av/ 2)
determining a length ulen between adjacent sample points along the u axis and a length vlen between adjacent sample points along the v axis as follows:
u len= au /( n− 1)
v len= av /( n− 1)
determining a stride value as follows:
stride= v len*( Uw*D )+ u len* D
where Uw is a width of the texture in texels along the u axis and D is a data size for each texel in memory;
for each of the n sample points, loading texture data for such sample point and applying a filter to the first sample point using the loaded texture data for such sample point to generate a sample result;
for each of the n sample points after a first sample point, using the stride value to initiate a prefetch of the texture data for such sample point prior to attempting to load the texture data for such sample point; and
averaging the sample results for the n sample points.
2. A circuit arrangement, comprising:
a memory storage element; and
processing logic coupled to the memory storage element and configured to perform anisotropic texture filtering using a texture defined in a texel coordinate system having u and v axes and a scene defined in a pixel coordinate system having x and y axes, the processing logic configured to, for an initial sample point in the texture at u,v coordinates:
determine a line of anisotropy, including determine au, av values for the line of anisotropy as follows:
au =max( du/dx, du/dy )
av =max( dv/dx, dv/dy )
where du/dx is a ratio between texel coordinates along the u axis and pixel coordinates along the x axis, du/dy is a ratio between texel coordinates along the u axis and pixel coordinates along the y axis, dv/dx is a ratio between texel coordinates along the v axis and pixel coordinates along the x axis, and dv/dy is a ratio between texel coordinates along the v axis and pixel coordinates along the y axis;
determine n sample points along the line of anisotropy, including determine ui, vi coordinates for each sample point i, where i=0 to n−1, as follows:
ui=u +( i*au /( n− 1)− au/ 2)
vi=v +( i*av /( n− 1)− av/ 2)
determine a length ulen between adjacent sample points along the u axis and a length vlen between adjacent sample points along the v axis as follows:
u len= au /( n− 1)
v len= av /( n− 1)
determine a stride value as follows:
stride= v len*( Uw*D )+ u len* D
where Uw is a width of the texture in texels along the u axis and D is a data size for each texel in memory;
for each of the n sample points, load texture data for such sample point and apply a filter to the first sample point using the loaded texture data for such sample point to generate a sample result;
for each of the n sample points after a first sample point, use the stride value to initiate a prefetch of the texture data for such sample point prior to attempting to load the texture data for such sample point; and
average the sample results for the n sample points.