texm3x2tex

Performs the final row of a 3×2 matrix multiply and uses the result to do a texture lookup. texm3x2tex must be used in conjunction with the texm3x2pad instruction.

texm3x2tex dest, src

Registers

To learn more about registers, see Registers.

Remarks

The instruction is used as one of two instructions representing a 3×2 matrix multiply operation. This instruction must be used with the texm3x2pad.

When using these two 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).
texm3x2pad  t(m),   t(n)      // where m > n
                              // Perform first row of matrix multiply.
texm3x2tex  t(m+1), t(n)      // Perform second row of matrix multiply 
                              // to get (u,v) to sample texture 
                              // associated with stage m+1.

Here is more detail about how the 3×2 multiply is accomplished.

// The texm3x2pad instruction performs the first row of the multiply to find u'.
u' = t(n)RGB • TextureCoordinates(stage m)UVW   

// The texm3x2tex instruction performs the second row of the multiply to find v'.
v' = t(n)RGB • TextureCoordinates(stage m+1)UVW   

// The texm3x2tex instruction samples the texture on stage (m+1) with (u',v') and 
// stores the result in t(m+1).
t(m+1)RGB = TextureSample(stage m+1)RGB using (u', v') 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.
texm3x2pad  t1,  t0   // First row of matrix multiply.
texm3x2tex  t2,  t0   // Second row of matrix multiply to get (u,v)
                      // with which to sample texture in stage 2.
mov r0, t2            // Output result.

// This example requires the following textures in the following texture stages.
//
// Stage 0 takes a map with (x,y,z) perturbation data.
//
// Stage 1 holds texture coordinates. No texture is required in the texture stage.
//
// Stage 2 holds both texture coordinates as well as a 2-D texture set at 
// that texture stage.