code: def billboard_matrix():
      """
      Removes rotational components of
      current matrix so that primitives
      are always drawn facing the viewer.
  
      |1|0|0|x|
      |0|1|0|x|
      |0|0|1|x| (x means left unchanged)
      |x|x|x|x|
      """
      m = get_model_matrix()
      # XXX: for i in range(11): m[i] = i ?
      m[0] = 1
      m[1] = 0
      m[2] = 0
      m[4] = 0
      m[5] = 1
      m[6] = 0
      m[8] = 0
      m[9] = 0
      m[10] = 1
      pgl.glLoadMatrixf(m)
  
imports: import pyglet.gl
  from sympy.core import S
label_desc: Use image node_id 10 for calling a global function with example usage: billboard_matrix() without return types