Fog Color

Fog color for both pixel and vertex fog is set through the D3DRS_FOGCOLOR render state. The render state values can be any RGB color, specified as an RGBA color. The alpha component is ignored.

The following C++ example sets the fog color to white.

/* For this example, the d3dDevice variable is
* a valid pointer to an IDirect3DDevice9 interface.
*/
HRESULT hr;
hr = d3dDevice->SetRenderState(
                    D3DRS_FOGCOLOR,
                    0x00FFFFFF); // Highest 8 bits are not used.
if(FAILED(hr))
    return hr;

Fog is applied differently by the fixed function pipeline and the programmable pipeline.

1. If the driver supports D3DPMISCCAPS_FOGANDSPECULARALPHA:
   • If the fixed function pipeline is used and D3DRS_FOGCOLOR is set, v1.w (in the pixel shader) equals the value set in fog renderstate.
   • If the programmable pipeline is used, then v1.w (in the pixel shader) equals 0, even if oD1.w is explicitly written in a vertex shader.
2. If the driver does NOT support D3DPMISCCAPS_FOGANDSPECULARALPHA:
   • If the fixed function pipeline is used and D3DRS_FOGCOLOR is set, then v1.w (in the pixel shader) equals value set in fog renderstate.
   • If oFog is explicitly written in a vertex shader, v1.w (in the pixel shader) equals oFog, clamped between 0 and 1.
   • If neither of the above two cases applies, v1.w (in the pixel shader) equals 0, even if oD1.w is explicitly written in a vertex shader.

For more information, see D3DPMISCCAPS.