code: def perspective(fovy, aspect, znear, zfar):
      h = math.tan(fovy / 360.0 * math.pi) * znear
      w = h * aspect
      return frustum(-w, w, -h, h, znear, zfar)
  
file_path: vispy/examples/gloo/gl/cube.py
imports: import math
  import numpy
  from vispy import app
  from vispy.gloo import gl
label_desc: Use image node_id 5 for calling a global function with example usage: perspective(fovy, aspect, znear, zfar) and returns: frustum