how to build Texture Coordinate Transformations Matrix in Direct3D

Question

I know there is a function in D3D that transforms the texture coordinate:

d3dDevice->SetTransform( D3DTS_TEXTURE0, &matrix );

The problem is how I could get the matrix. For example, I now have texture offset, scale, rotation, and brightness. How should I set that matrix?

Answer 1

Transforms. There are links to the D3DX Utility Library methods on that page.

Answer 2

Let us consider you have collection of images of same width(txTxWidth) and height(txTxHight) in a texture atlas of width (txFullWidth) and height(txFullHeight).

step 1: Build a 4x4 scale matrix of size equal to an image cell in a texture atlas.

D3DXMatrixScaling(&matScale, txTxWidth/txFullWidth, txTxHeight/txFullHeight, 1.0f);

step 2: Build a 4x4 translation matrix using the (x,y) offset and the image cell width and height

   D3DXMATRIX matTrans;
   matTrans._13 = x / txFullWidth; // X origin
   matTrans._23 = y / txFullHeight; // Y origin
   matTrans._31 = txTxWidth / txFullWidth;  // Width;   
   matTrans._32 = txTxHeight / txFullHeight; // Height

step: 4: Don't forgot to transpose the translation matrix

   D3DXMATRIX trpos_matTrans;
   D3DXMatrixTranspose(&trpos_matTrans,&matTrans);

step 3: Build a 4x4 rotation matrix according to your requirement.

 D3DXMatrixRotationX(&matRot, D3DXToRadian(0.0f));

step 4: Multiplication

 matix = matScale * matRot * trpos_matTrans ; // SRT

step 5: Set the Texture Transform

device->SetTransform(D3DTS_TEXTURE0, &matrix);

step 6: Set the Texture Stage 0

device->SetTextureStageState(0, D3DTSS_TEXTURETRANSFORMFLAGS,   D3DTTFF_COUNT2);

Hope this will solve your propblem. Enjoy !!!