// Create view and projection matrices, based on the current camera and
// using the imposter quad as the viewing plane.
void ImposterSystem::CreateMatrices(
			const D3DXVECTOR3& curCameraPos,
			const D3DXVECTOR3& curCameraUp,
			D3DXMATRIX& imposterViewMatrix, D3DXMATRIX& imposterProjMatrix,
   			Imposter* pImposter, float imposterNearPlane, float imposterFarPlane)
{
	D3DXMatrixLookAtLH(&imposterViewMatrix, &curCameraPos,
                         &pImposter->centre, &curCameraUp);

	D3DXVECTOR3 widthVec = pImposter->verts[1].pos - pImposter->verts[0].pos;
	D3DXVECTOR3 heightVec = pImposter->verts[5].pos - pImposter->verts[0].pos;
	float viewWidth = D3DXVec3Length(&widthVec);
	float viewHeight = D3DXVec3Length(&heightVec);
	D3DXMatrixPerspectiveLH(&imposterProjMatrix, viewWidth, viewHeight,
				    imposterNearPlane, imposterFarPlane);
}