texm3x3tex (Pixel Shader)

Performs a 3x3 matrix multiply and uses the result to do a texture lookup. texm3x3tex (Pixel Shader) must be used with two texm3x3pad instructions.

Syntax

texm3x3tex (Pixel Shader) dest, src

Registers

dest
Destination register.
src
Input source register.

Remarks

Pixel shader versions 1_1 1_2 1_3 1_4 2_0 2_x 2_sw 3_0 3_sw
texm3x3tex x x x
This instruction is used as the final of three instructions representing a 3x3 matrix multiply operation, followed by a texture lookup. The 3x3 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 3x3 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 the texm3x3pad instruction. 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 3x3 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.

Examples

Here is an example shader with the texture maps identified and the texture stages identified.
ps_1_1
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 
mov r0, t3            //   stage 3 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 3x3 matrix. Any texture assigned to stage 1 is ignored.
Texture coordinate set 2 is assigned to row 2 of the 3x3 matrix. Any texture assigned to stage 2 is ignored.
Texture coordinate set 3 is assigned to row 3 of the 3x3 matrix. A volume or cube texture should be set to stage 3 for lookup by the transformed 3-D vector.

Instruction Information

Minimum operating systems Windows 98