Special Effects

This topic contains examples of special effects accomplished with texture coordinate processing.

• Animating textures (by translation or rotation) on a model
• Creating texture coordinates as a linear function of a model's camera-space position
• Performing environment mapping with a cubic environment map
• Performing projective texturing

Animating textures (by translation or rotation) on a model

• Define two-dimensional (2-D) texture coordinates in your vertex format.

  // Use a single texture, with 2-D texture coordinates. This
  // bit-pattern should be expanded to include position, normal, 
  // and color information as needed.
  DWORD dwFVFTex = D3FVF_TEX1 | D3DFVF_TEXCOORDSIZE2(0);

• Configure the rasterizer to use 2-D texture coordinates.

  SetTextureStageState(0, D3DTSS_TEXTURETRANSFORMFLAGS, D3DTTFF_COUNT2);

• Define and set an appropriate texture coordinate transformation matrix.

  // M is a D3DMATRIX being set to translate texture
  // coordinates in the U and V directions.
  //      1   0  0  0
  //      0   1  0  0
  //      du dv  1  0 (du and dv change each frame)
  //      0   0  0  1
  
  D3DMATRIX M = D3DXMatrixIdentity(); // declared in d3dutil.h
  M._31 = du; 
  M._32 = dv; 

Creating texture coordinates as a linear function of a model's camera-space position

• Use the D3DTSS_TCI_CAMERASPACEPOSITION flag to instruct the system to pass the vertex position, in camera space, as input to a texture transformation.

  // The input vertices have no texture coordinates, saving 
  // bandwidth. Three texture coordinates are generated by 
  // using vertex position in camera space (x, y, z).
  SetTextureStageState(0, D3DTSS_TEXCOORDINDEX, D3DTSS_TCI_CAMERASPACEPOSITION);

• Instruct the rasterizer to expect 2-D texture coordinates.

  // Two output coordinates are used.
  SetTextureStageState(0, D3DTSS_TEXTURETRANSFORMFLAGS, D3DTTFF_COUNT2);

• Define and set a matrix that applies a linear function.

  // Generate texture coordinates as linear functions 
  // so that:
  //      u = Ux*x + Uy*y + Uz*z + Uw 
  //      v = Vx*x + Vy*y + Vz*z + Vw
  // The matrix M for this case is:
  //      Ux  Vx  0  0 
  //      Uy  Vy  0  0 
  //      Uz  Vz  0  0 
  //      Uw  Vw  0  0 
  
  SetTransform(D3DTS_TEXTURE0, &M);

Performing environment mapping with a cubic environment map

• Use the D3DTSS_TCI_CAMERASPACEREFLECTIONVECTOR flag to instruct the system to automatically generate texture coordinates as reflection vectors for cubic mapping.

  SetTextureStageState(0, D3DTSS_TEXCOORDINDEX, D3DTSS_TCI_CAMERASPACEREFLECTIONVECTOR);

• Instruct the rasterizer to expect texture coordinates with three elements.

  SetTextureStageState(0, D3DTSS_TEXTURETRANSFORMFLAGS, D3DTTFF_COUNT3);

Performing projective texturing

• Use the D3DTSS_TCI_CAMERASPACEPOSITION flag to instruct the system to pass the vertex position as input to a texture transformation matrix.

  SetTextureStageState(0, D3DTSS_TEXCOORDINDEX, D3DTSS_TCI_CAMERASPACEPOSITION);

• Create and apply the texture projection matrix. This is beyond the scope of this documentation, and is the topic of several industry articles.
• Instruct the rasterizer to expect three-element projected texture coordinates.

  // Two output coordinates are used.
  
  SetTextureStageState(0, D3DTSS_TEXTURETRANSFORMFLAGS, D3DTTF_PROJECTED | D3DTTFF_COUNT3);