public void getTriangle(int index, Triangle tri) {
        getTriangle(index, tri.get1(), tri.get2(), tri.get3());
        tri.setIndex(index);
        tri.setCenter(null); // invalidate previously cached centroid, if any
        tri.setNormal(null);
    }
Gets the triangle vertex positions at the given triangle index
and stores them into the {@link Triangle} argument.
Also sets the triangle index to the <code>index</code> argument.

@param index The index of the triangle.
Should be between 0 and {@link #getTriangleCount()}.

@param tri The triangle to store the positions in
jme3-core/src/main/java/com/jme3/scene/Mesh.java