texm3x3spec

Performs a 3×3 matrix multiply and uses the result to perform a texture lookup. This can be used for specular reflection and environment mapping. texm3x3spec must be used in conjunction with two texm3x3pad instructions.

texm3x3spec dest, src0, src1, src2

Registers

To learn more about registers, see Registers.

Remarks

This instruction performs the final row of a 3×3 matrix multiply, uses the resulting vector as a normal vector to reflect an eye-ray vector, and then uses the reflected vector to perform a texture lookup. The shader reads the eye-ray vector from a constant register. The 3×3 matrix multiply is typically useful for orienting a normal vector to the correct tangent space for the surface being rendered.

The 3×3 matrix is comprised of the texture coordinates of the third texture stage and the two preceding texture stages. The resulting post reflection vector (u,v,w) is used to sample the texture on the final texture stage. Any texture assigned to the preceding two texture stages is ignored.

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.
texm3x3spec t(m+2), t(n), c0  // Perform third row of matrix multiply.
                              // Then do a texture lookup on the texture
                              // associated with texture stage m+2.

// 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  

// The texm3x3spec instruction then does a reflection calculation.
(u'', v'', w'') = 2*[(N•E)/(N•N)]*N - E
// where the normal N is given by 
// N = (u', v', w')
// and the eye-ray vector E is given by the constant register
// E = c# (Any constant register--c0, c1, c2, etc.--can be used.)

// Lastly, the texm3x3spec 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 and
// the texture stages identified.
ps.1.0
tex t0                    // Bind texture in stage 0 to register t0 (tn must
                          // be defined in some way before it is used).
texm3x3pad  t1,  t0       // First row of matrix multiply.
texm3x3pad  t2,  t0       // Second row of matrix multiply.
texm3x3spec t3,  t0,  c#  // Third row of matrix multiply to get a 3-vector.
                          // Reflect 3-vector by the eye-ray vector in c#.  
                          // Use reflected vector to lookup texture in
                          // 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 coordinates at stage n defines where to sample this 
// normal map.
//
// Texture coordinate set m is assigned to row 1 of the 3×3 matrix. 
// Any texture assigned to stage m is ignored.
//
// Texture coordinate set m+1 is assigned to row 2 of the 3×3 matrix. 
// Any texture assigned to stage m+1 is ignored.
//
// Texture coordinate set m+2 is assigned to row 3 of the 3×3 matrix. 
// Stage m+2 is assigned a volume or cube texture map. The texture provides 
// color data (RGBA). 
//
// The eye-ray vector E is given by a 
// constant register E = c#.