To enable vertex fog in a C++ application

1. Enable fog blending by setting D3DRENDERSTATE_FOGENABLE to TRUE.
2. Set the fog color in the D3DRENDERSTATE_FOGCOLOR render state.
3. Choose the desired fog formula by setting the D3DRENDERSTATE_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 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_lpDevice is a valid
// pointer to an IDirect3DDevice7 interface.
void SetupVertexFog(DWORD dwColor, DWORD dwMode, BOOL fUseRange, FLOAT fDensity)
{
    float fStart = 0.5f,    // linear fog distances
          fEnd   = 0.8f;
 
    // Enable fog blending.
    g_lpDevice->SetRenderState(D3DRENDERSTATE_FOGENABLE, TRUE);
 
    // Set the fog color.
    g_lpDevice->SetRenderState(D3DRENDERSTATE_FOGCOLOR, dwColor);
    
    // Set fog parameters.
    if(D3DFOG_LINEAR == dwMode)
    {
        g_lpDevice->SetRenderState(D3DRENDERSTATE_FOGVERTEXMODE, dwMode);
        g_lpDevice->SetRenderState(D3DRENDERSTATE_FOGSTART, *(DWORD *)(&fStart));
        g_lpDevice->SetRenderState(D3DRENDERSTATE_FOGEND,   *(DWORD *)(&fEnd));
    }
    else
    {
        g_lpDevice->SetRenderState(D3DRENDERSTATE_FOGVERTEXMODE, dwMode);
        g_lpDevice->SetRenderState(D3DRENDERSTATE_FOGDENSITY, *(DWORD *)(&fDensity));
    }

    // Enable range-based fog if desired (only supported for vertex fog).
    // For this example, it is assumed that fUseRange 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(fUseRange)
        g_lpDevice->SetRenderState(
                       D3DRENDERSTATE_RANGEFOGENABLE,
                       TRUE);
}

Note  Some fog parameters are required as floating-point values, even though the IDirect3DDevice7::SetRenderState method only accepts DWORD values in the second parameter. The preceding 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, then dereferencing them.

To enable vertex fog from a Visual Basic application

1. Enable fog blending by setting D3DRENDERSTATE_FOGENABLE to True.
2. Set the fog color in the D3DRENDERSTATE_FOGCOLOR render state.
3. Choose the desired fog formula by setting the D3DRENDERSTATE_FOGVERTEXMODE render state to a member of the CONST_D3DFOGMODE enumeration.
4. Set the fog parameters as desired for the selected fog formula in the render states.

The following Visual Basic example code 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_d3dDevice is a valid
' reference to a Direct3DDevice7 object.
Sub SetupVertexFog(lColor As Long, Mode As CONST_D3DFOGMODE, _
                   bUseRange As Boolean, Optional Density As Single)

    Dim StartFog As Single, _
        EndFog As Single
    
    ' Set linear fog distances
    StartFog = 0.5: EndFog = 0.8
 
    ' Enable fog blending.
    Call g_d3dDevice.SetRenderState(D3DRENDERSTATE_FOGENABLE, True)
 
    ' Set the fog color.
    Call g_d3dDevice.SetRenderState(D3DRENDERSTATE_FOGCOLOR, lColor)
    
    ' Set fog parameters.
    If Mode = D3DFOG_LINEAR Then
        Call g_d3dDevice.SetRenderState(D3DRENDERSTATE_FOGVERTEXMODE, Mode)
        Call g_d3dDevice.SetRenderStateSingle(D3DRENDERSTATE_FOGSTART, StartFog)
        Call g_d3dDevice.SetRenderStateSingle(D3DRENDERSTATE_FOGEND, EndFog)
    Else
        Call g_d3dDevice.SetRenderState(D3DRENDERSTATE_FOGVERTEXMODE, Mode)
        Call g_d3dDevice.SetRenderStateSingle(D3DRENDERSTATE_FOGDENSITY, Density)
    End If

    ' Enable range-based fog if desired (only supported for vertex fog).
    ' For this example, it is assumed that bUseRange is set to True only
    ' if the driver exposes the D3DPRASTERCAPS_FOGRANGE capability.
    '
    ' Note: this is slightly more performance intensive
    '       than non-range-based fog.
    If bUseRange = True Then
        Call g_d3dDevice.SetRenderState( _
                       D3DRENDERSTATE_RANGEFOGENABLE, True)
    End If
End Sub