texm3x3tex

Performs a 3×3 matrix multiply and uses the result to do a texture lookup. texm3x3tex must be used with two texm3x3pad instructions.

texm3x3tex dest, src

To learn more about registers, see Registers.

Remarks

This instruction is used as the final of three instructions representing a 3×3 matrix multiply operation, followed by a texture lookup. The 3×3 matrix is comprised of the texture coordinates of the third texture stage and the two preceding texture stages. The resulting three-component vector (u,v,w) is used to sample the texture in stage 3. Any texture assigned to the preceding two texture stages is ignored. The 3×3 matrix multiply is typically useful for orienting a normal vector to the correct tangent space for the surface being rendered.

This instruction must be used with two texm3x3pad instructions. Texture registers must use the following sequence.

tex t(n)                 // Define tn as a standard 3-vector (tn must
                         // be defined in some way before it is used).
texm3x3pad t(m),   t(n)  // where m > n
                         // Perform first row of matrix multiply.
texm3x3pad t(m+1), t(n)  // Perform second row of matrix multiply.
texm3x3tex t(m+2), t(n)  // Perform third row of matrix multiply to get a
                         // 3-vector with which to sample texture
                         // associated with texture stage m+2.

Here is more detail about how the 3×3 multiply is accomplished.

// The first texm3x3pad instruction performs the first row of the multiply 
// to find u'.
u' = TextureCoordinates(stage m)UVW • t(n)RGB   

// The second texm3x3pad instruction performs the second row of the multiply 
// to find v'.
v' = TextureCoordinates(stage m+1)UVW • t(n)RGB   

// The texm3x3spec instruction performs the third row of the multiply
// to find w'.
w' = TextureCoordinates(stage m+2)UVW • t(n)RGB  

// Lastly, the texm3x3tex instruction samples t(m+2) with (u',v',w')
// and stores the result in t(m+2).
t(m+2)RGBA = TextureSample(stage m+2)RGBA using (u', v', w') as coordinates.

Example

// Here is an example shader with the texture maps identified and
// the texture stages identified.
ps.1.0
tex t0                // Bind texture in stage 0 to register t0.
texm3x3pad  t1,  t0   // First row of matrix multiply.
texm3x3pad  t2,  t0   // Second row of matrix multiply.
texm3x3tex  t3,  t0   // Third row of matrix multiply to get a
                      // 3-vector with which to sample texture at stage 3
mov r0, t3            // output result.

// This example requires the following texture stage setup.
//
// Stage 0 is assigned a texture map with normal data. This is often 
// referred to as a bump map. The data is (XYZ) normals for 
// each texel. Texture coordinate set 0 defines how to sample this 
// normal map.
//
// Texture coordinate set 1 is assigned to row 1 of the 3×3 matrix. 
// Any texture assigned to stage 1 is ignored.
//
// Texture coordinate set 2 is assigned to row 2 of the 3×3 matrix. 
// Any texture assigned to stage 2 is ignored.
//
// Texture coordinate set 3 is assigned to row 3 of the 3×3 matrix. 
// A volume or cube texture should be set to stage 3  for lookup by the 
// transformed 3-D vector.
//