public override void DrawIndexedInstanced(PrimitiveType primType, int indexCountPerInstance, int startIndex, int baseVertex, int instanceCount)
{
XFG.PrimitiveType xnaPrim;
int numPrims;
ComputeXNADrawCall(primType, indexCountPerInstance, out xnaPrim, out numPrims);
_device.DrawInstancedPrimitives(xnaPrim, baseVertex, 0, indexCountPerInstance, startIndex, numPrims, instanceCount);
}