Using Vertex Fog

Use the following steps to enable vertex fog in your application.

To enable vertex fog in a C++ application

1. Enable fog blending by setting D3DRS_FOGENABLE to TRUE.
2. Set the fog color in the D3DRS_FOGCOLOR render state.
3. Choose the desired fog formula by setting the D3DRS_FOGVERTEXMODE render state to a member of the D3DFOGMODE enumerated type.
4. Set the fog parameters as desired for the selected fog formula in the render states.

The following code example, written in C++, shows what these steps might look like in code.

// For brevity, error values in this example are not checked 
// after each call. A real-world application should check 
// these values appropriately.
//
// For the purposes of this example, g_pDevice is a valid
// pointer to an IDirect3DDevice8 interface.
void SetupVertexFog(DWORD Color, DWORD Mode, BOOL UseRange, FLOAT Density)
{
    float Start = 0.5f,    // Linear fog distances
          End   = 0.8f;
 
    // Enable fog blending.
    g_pDevice->SetRenderState(D3DRS_FOGENABLE, TRUE);
 
    // Set the fog color.
    g_pDevice->SetRenderState(D3DRS_FOGCOLOR, Color);
    
    // Set fog parameters.
    if(D3DFOG_LINEAR == Mode)
    {
        g_pDevice->SetRenderState(D3DRS_FOGVERTEXMODE, Mode);
        g_pDevice->SetRenderState(D3DRS_FOGSTART, *(DWORD *)(&Start));
        g_pDevice->SetRenderState(D3DRS_FOGEND,   *(DWORD *)(&End));
    }
    else
    {
        g_pDevice->SetRenderState(D3DRS_FOGVERTEXMODE, Mode);
        g_pDevice->SetRenderState(D3DRS_FOGDENSITY, *(DWORD *)(&Density));
    }

    // Enable range-based fog if desired (only supported for
    // vertex fog). For this example, it is assumed that UseRange
    // is set to a nonzero value only if the driver exposes the 
    // D3DPRASTERCAPS_FOGRANGE capability.
    // Note: This is slightly more performance intensive
    //       than non-range-based fog.
    if(UseRange)
        g_pDevice->SetRenderState(
                       D3DRS_RANGEFOGENABLE,
                       TRUE);
}

Some fog parameters are required as floating-point values, even though theIDirect3DDevice8::SetRenderState method only accepts DWORD values in the second parameter. This example successfully provides the floating-point values to these methods without data translation by casting the addresses of the floating-point variables as DWORD pointers, and then dereferencing them.

See Also

Vertex Fog

 Last updated on Thursday, April 08, 2004

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