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Problem with stencil buffer

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Howdy, I just have a quick question that's really confusing me. I'm trying to do some very simple shadows using the stencil buffer but instead of the shadow appearing black and alpha blended with the ground it appears white (with the correct shape) and not alpha blended. I have closely followed several tutorials but I am at a loss as to why this is happening. First of all when I'm initializing everything I call SetupStencilBuffer()
void SetupStencilBuffer()
    Device->SetRenderState(D3DRS_STENCILENABLE,    true);
    Device->SetRenderState(D3DRS_STENCILFUNC,      D3DCMP_EQUAL);
    Device->SetRenderState(D3DRS_STENCILREF,       0x0);
    Device->SetRenderState(D3DRS_STENCILMASK,      0xffffffff);
    Device->SetRenderState(D3DRS_STENCILWRITEMASK, 0xffffffff);
    Device->SetRenderState(D3DRS_STENCILZFAIL,     D3DSTENCILOP_KEEP);
    Device->SetRenderState(D3DRS_STENCILFAIL,      D3DSTENCILOP_KEEP);
    Device->SetRenderState(D3DRS_STENCILPASS,      D3DSTENCILOP_INCR);

In my render loop I then do my drawing
    //Render the sky box
    Device->SetTransform(D3DTS_WORLD, &skyPosition);

    //Draw the pistons
    Device->SetTransform(D3DTS_WORLD, &engPosition);

    //Draw the engine transparently
    Device->SetRenderState(D3DRS_ALPHABLENDENABLE, true);
    Device->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_ZERO);
    Device->SetTransform(D3DTS_WORLD, &engPosition);
    Device->SetRenderState(D3DRS_ALPHABLENDENABLE, false);

    //Draw the shadow of the engine

castShadow() consists of
void castShadow()
    //Create the light ray plane used casting the shadow
    D3DXVECTOR4 lightRay(0.0f, 50.0f, 0.0f, 1.0f);
    D3DXPLANE basePlane(0.0f, 1.0f, 0.0f, 9.0f);

    //Position us at shadow position
    D3DXMatrixShadow(&S, &lightRay, &basePlane);
    D3DXMATRIX worldShadow;
    worldShadow = engPosition * S;
    Device->SetTransform(D3DTS_WORLD, &worldShadow);

    //Set our render states
    Device->SetRenderState(D3DRS_ALPHABLENDENABLE, true);
    Device->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_SRCALPHA);
    Device->SetRenderState(D3DRS_STENCILENABLE, true);   
    Device->SetRenderState(D3DRS_ZENABLE, false);
    //Draw the actual shadow (model drawn with a black D3DMATERIAL9 with diffuse    
    //transparency of 0.5f and SetTexture(0, 0))

    //Set our render states back
    Device->SetRenderState(D3DRS_ZENABLE, true);
    Device->SetRenderState(D3DRS_ALPHABLENDENABLE, false);
    Device->SetRenderState(D3DRS_STENCILENABLE,    false);

just for the sake of clarity I am clearing my buffer every frame with
Device->Clear( 0, NULL, 
      D3DCOLOR_COLORVALUE(0.0f,0.0f,0.0f,1.0f), 1.0f, 0 );

Any idea of where I might be going wrong would be greatly appreciated. Paul

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Have you made sure lighting is enabled, the appropriate ambient lighting is set, and the material of your shadow mesh has an ambient component?

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