texm3x2tex - ps

Performs the final row of a 3x2 matrix multiply and uses the result to do a texture lookup. texm3x2tex must be used in conjunction with the texm3x2pad - ps instruction.


texm3x2tex dst, src



  • dst is the destination register.
  • src is a source register.


Pixel shader versions1_11_21_31_42_02_x2_sw3_03_sw


The instruction is used as one of two instructions representing a 3x2 matrix multiply operation. This instruction must be used with the texm3x2pad - ps instruction.

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 3x2 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


Here is an example shader with the texture maps and the texture stages identified.

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 2D texture set at that texture stage.

Related topics

Pixel Shader Instructions