Replace PyOpenGL with Qt OpenGL API

[Tom Goddard]

Might want to drop PyOpenGL and call OpenGL functions through PySide2.

PyOpenGL is poorly maintained. This leads to a lot of wasted time fixing its problems. The current one I am working on is #3760 where the latest PyOpenGL 3.1.5 is generate warnings on startup about missing numpy_formathandler. This took almost a day of debugging and trying to fix so far -- it is just because the PyPi PyOpenGL builds are wrong, forgot to include numpy before building. I made a PyOpenGL ticket for it, no response.

Qt / PySide2 offers a full OpenGL API. For example, to use from PySide2 15.1

from PySide2.QtOpenGLFunctions import QOpenGLFunctions_3_3_Core as GL
GL.glClear(GL.GL_COLOR_BUFFER_BIT)

Actually this does not work. Although glClear is in GL, the constants don't appear to be, ie GL.GL_COLOR_BUFFER_BIT gets an attribute error.

It is hard to find examples using this, so it may be even less usable than PyOpenGL.

[Tom Goddard]

If I instead use

GL = qc.versionFunctions()

where qc is our QOpenGLContext instance then GL is a QAbstractOpenGLFunctions and has no methods, ie GL.glClear gives an attribute error. In PyQt5 this works correctly. Here is a PySIde2 bug report about this from Feb 2019, has not been resolved

​https://bugreports.qt.io/browse/PYSIDE-955

[Tom Goddard]

There is no documentation for module PySide2.QtOpenGLFunctions.

​https://doc.qt.io/qtforpython-5/modules.html

Not sure what to make of that. Is it not supported? Is it just an experiment for PySide6 for Qt6?

[Tom Goddard]

I asked on the PySide2 mailing list if desktop OpenGL is usable:

​https://lists.qt-project.org/pipermail/pyside/2020-December/003041.html

Begin forwarded message:

From: Tom Goddard
Subject: Is QOpenGLFunctions_3_3_Core supported in PySide2
Date: December 11, 2020 at 8:03:09 PM PST
To: pyside@…

I am trying to figure out whether PySide2 offers an API for desktop OpenGL, e.g. 3.3 core profile. Currently I use PyOpenGL which is poorly maintained and would like to switch to using PySide2 OpenGL bindings if possible. Here is the Qt documentation of QOpenGLFunctions_3_3_Core that I would like to use from PySide2.

​https://doc.qt.io/qt-5/qopenglfunctions-3-3-core.html

Here are failed attempts. I am using PySide 15.1 on macOS 10.15.

1) First the class is not in QtGui which is where the live in C++ Qt

from PySide2.QtGui import QOpenGLFunctions_3_3_Core
-> import error, no such name

2) But there is an undocumented QtOpenGLFunctions module that has it

from PySide2.QtOpenGLFunctions import QOpenGLFunctions_3_3_Core as GL

and it contains the functions, e.g. GL.glClear but does not have the constants

GL.GL_COLOR_BUFFER_BIT
-> attribute error

dir(GL) -> shows only glXYZ functions not any GL_XYZ constants.

3) If I take my QOpenGLContext instance (that I currently use with PyOpenGL) qc and try to get the functions

GL = qc.versionFunctions()

it gives a QAbstractOpenGLFunctions instance with no opengl methods

GL.glClear
-> attribute error

There is a PySide2 bug report about that from Feb 2019 with no resolution

​https://bugreports.qt.io/browse/PYSIDE-955

4) In PyQt5 approach 3 works

GL = qc.versionFunctions()
GL
-> <PyQt5._QOpenGLFunctions_4_1_Core.QOpenGLFunctions_4_1_Core at 0x14e325730>

and this module has glClear and GL_COLOR_BUFFER_BIT, seems to have what is needed although I have not tried using it.

Thanks for shedding any light on the using the desktop OpenGL API from PySide2.

Tom Goddard
ChimeraX molecular visualization developer