HRESULT SetUmbra(D3DVALUE rvAngle);
Sets the angle of the umbra cone.
·Returns D3DRM_OK if successful, or an error otherwise. For a list of possible return codes, see Direct3D Retained-Mode Return Values.
rvAngle
New umbra angle. This angle must be less than or equal to the angle of the penumbra. If you try to set the umbra angle to greater than the penumbra angle, the penumbra angle will be set equal to the umbra angle. The default value is 0.4 radians.