DirectDraw Surface Transparent Blt

void CopySurface(IDirectDrawSurface7 *lpSurfaceDst, RECT &rectTarget, IDirectDrawSurface7 *lpSurfaceSrc, RECT &rectSrc)
{
DDBLTFX ddbltfx;
ZeroMemory(&ddbltfx, sizeof(ddbltfx));
ddbltfx.dwSize = sizeof(ddbltfx);

DDCOLORKEY colorKey = {RGB(0,0,0), RGB(0,0,0)};    // Transparent Color - black
ddbltfx.ddckSrcColorkey = colorKey;

DWORD flags = DDBLT_ASYNC | DDBLT_KEYSRCOVERRIDE;

HRESULT hr = lpSurfaceDst->Blt(&rectTarget, lpSurfaceSrc, &rectSrc, flags, &ddbltfx);
if (FAILED(hr)) {
TRACE("[%s] hr:0x%x\n", __FUNCTION__, hr);
}
}