# Thread: how can i multiply a vertex coord by a matrix in a vp?

1. ## how can i multiply a vertex coord by a matrix in a vp?

hi, i need to multiply a vertex's texture coordinates by the texture matrix in order to make projective texturing in a vertex program. The problem is that i have little knowledge about matrix math and i don't know how to do the multiplication of a vector by a matrix, can someone help me, please?

2. ## Re: how can i multiply a vertex coord by a matrix in a vp?

hey jcabeleira, maybe something like this:

Code :
```...

ATTRIB  tc = vertex.texcoord[?];
TEMP    result;
PARAM   texMat[4] = { state.matrix.texture[?] };

# matrix multiply is just 4 dot products
# tc (row) into each texture matrix column
DP4     result.x, tc, texMat[0];
DP4     result.y, tc, texMat[1];
DP4     result.z, tc, texMat[2];
DP4     result.w, tc, texMat[3];

...```
hope this helps!

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