Anisotropic texture filtering with texture data prefetching

• US 8,217,953 B2
• Filed: 04/25/2008
• Issued: 07/10/2012
• Est. Priority Date: 04/25/2008
• Status: Expired due to Fees

• Current Assignee: Activision Publishing Incorporated (Microsoft Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Comparan, Miguel, Mejdrich, Eric Oliver, Muff, Adam James, Tubbs, Matthew Ray
• Primary Examiner(s): Wu, Xiao M.
• Assistant Examiner(s): Tseng, Charles
• Application Number:
  US12/110,045
• Publication Number:
  US 20090315908A1
• Time in Patent Office: 1,537 Days
• Field of Search: 345582-588
• US Class Current: 345/582
• CPC Class Codes: G06T 15/04 Texture mapping
• CPC Class Codes: G06T 2200/12 involving antialiasing

Abstract

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.

Claims

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;

ulen=au/(n−

1)

vlen=av/(n−

1)

determining a stride value as follows;

stride=vlen*(Uw*D)+ulen*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;

ulen=au/(n−

1)

vlen=av/(n−

1)

determine a stride value as follows;

stride=vlen*(Uw*D)+ulen*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.