Bug: new viewer not working and reverting to classic mode on some Linux configuration

[abey79]

Symptom

show reverts to classic viewer with following note:

WARNING:root:!!! show: ModernGL not available, reverting to classic mode.

This may have several root cause. This issue is about failing to find the X11 library. It can be confirmed with the following command:

python -c "import moderngl;print(moderngl.create_standalone_context().info)"

The output should be similar to this:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File ".../lib/python3.8/site-packages/moderngl/context.py", line 1560, in create_standalone_context
    ctx.mglo, ctx.version_code = mgl.create_context(glversion=require, mode=mode, **settings)
  File ".../lib/python3.8/site-packages/glcontext/__init__.py", line 80, in create
    return x11.create_context(**kwargs)
Exception: (detect) libX11.so not loaded

Workaround

Run the following command:

python -c "from ctypes.util import find_library; print(find_library('X11'))"

Note the result. There are good chances that it is libX11.so.6 (but could be something else.

Running vpype with the following command should then work (use the actual result of the previous command instead of libX11.so.6:

GLCONTEXT_LINUX_LIBX11=libX11.so.6 vpype ...