How to Zoom in and out when mappviewer is running?

[MartikyHe]

When the mappviewer is refreshing, it seems that it is unable for users to zoom in and out to see clearer of the whole loop. How could this function be implemented?

[MartikyHe]

This is the error feedback:
Traceback (most recent call last):
File "/home/lib/python3.6/multiprocessing/process.py", line 258, in _bootstrap
self.run()
File "/home/lib/python3.6/multiprocessing/process.py", line 93, in run
self._target(*self._args, **self._kwargs)
File "/home/stereo_ptam/viewer.py", line 246, in view
gl.glClear(gl.GL_COLOR_BUFFER_BIT | gl.GL_DEPTH_BUFFER_BIT)
File "errorchecker.pyx", line 53, in OpenGL_accelerate.errorchecker._ErrorChecker.glCheckError (src/errorchecker.c:1218)
OpenGL.error.GLError: GLError(
err = 1280,
description = b'invalid enumerant',
baseOperation = glClear,
cArguments = (16640,)
)