A minimal OpenGL example in PyQt6 does not work. Error: "invalid operation" in glClearColor

Question

I try to run a very simple OpenGL example:

import sys

from OpenGL import GL as gl
from PyQt6.QtOpenGLWidgets import QOpenGLWidget
from PyQt6.QtWidgets import QApplication


class Widget(QOpenGLWidget):

    def __init__(self):
        super().__init__()
        self.setWindowTitle("PyQt6, OpenGL 3.3")
        self.resize(400, 400)

    def initializeGL(self):
        gl.glClearColor(0.5, 0.5, 0.5, 1)
    
    def paintGL(self):
        gl.glClear(gl.GL_COLOR_BUFFER_BIT)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec())

But I have this error:

Traceback (most recent call last):
  File "main.py", line 16, in initializeGL
    gl.glClearColor(0, 0, 0, 1)
  File "E:\ProgramFiles\Python\Python38\lib\site-packages\OpenGL\platform\baseplatform.py", line 415, in __call__
    return self( *args, **named )
  File "E:\ProgramFiles\Python\Python38\lib\site-packages\OpenGL\error.py", line 230, in glCheckError
    raise self._errorClass(
OpenGL.error.GLError: GLError(
        err = 1282,
        description = b'invalid operation',
        baseOperation = glClearColor,
        cArguments = (0, 0, 0, 1)
)

It is the same example but in PyQt5 that works:

import sys

from OpenGL import GL as gl
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication, QOpenGLWidget


class Widget(QOpenGLWidget):

    def __init__(self):
        super().__init__()
        self.setWindowTitle("PyQt5, OpenGL 3.3")
        self.resize(400, 400)

    def initializeGL(self):
        gl.glClearColor(0.5, 0.5, 0.5, 1)
    
    def paintGL(self):
        gl.glClear(gl.GL_COLOR_BUFFER_BIT)

if __name__ == "__main__":
    QApplication.setAttribute(Qt.AA_UseDesktopOpenGL)
    app = QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec_())

There are two differences:

• 1. QOpenGLWidget was moved to PyQt6.QtOpenGLWidgets
• 2. the line in the PyQt5 example: QApplication.setAttribute(Qt.AA_UseDesktopOpenGL)

Answer 1

This line:

QApplication.setAttribute(Qt.AA_UseDesktopOpenGL)

should be replaced with this:

QApplication.setAttribute(Qt.ApplicationAttribute.AA_UseDesktopOpenGL)

These changes also apply to PySide6:

1. OpenGL classes have been moved to a separate PyQt6.QtOpenGL namespace:

PyQt5:

from PyQt5.QtGui import (QOpenGLBuffer, QOpenGLShader, QOpenGLShaderProgram,
                         QOpenGLTexture)

PyQt6:

from PyQt6.QtOpenGL import (QOpenGLBuffer, QOpenGLShader, QOpenGLShaderProgram,
                            QOpenGLTexture)

2. The QOpenGLWidget class has been moved to the PyQt6.QtOpenGLWidgets namespace:

PyQt5:

from PyQt5.QtWidgets import QApplication, QOpenGLWidget

PyQt6:

from PyQt6.QtOpenGLWidgets import QOpenGLWidget

3. Changed enum for shader types:

PyQt5:

self.program.addShaderFromSourceCode(QOpenGLShader.Vertex, vertShaderSrc)
self.program.addShaderFromSourceCode(QOpenGLShader.Fragment, fragShaderSrc)

PyQt6:

self.program.addShaderFromSourceCode(QOpenGLShader.ShaderTypeBit.Vertex, vertShaderSrc)
self.program.addShaderFromSourceCode(QOpenGLShader.ShaderTypeBit.Fragment, fragShaderSrc)

4. Changed enum Target texture:

PyQt5:

self.texture = QOpenGLTexture(QOpenGLTexture.Target2D)

PyQt6:

self.texture = QOpenGLTexture(QOpenGLTexture.Target.Target2D)

5. Changed enum for setting texture filters:

PyQt5:

self.texture.setMinMagFilters(QOpenGLTexture.Linear, QOpenGLTexture.Linear)

PyQt6:

self.texture.setMinMagFilters(QOpenGLTexture.Filter.Linear, QOpenGLTexture.Filter.Linear)

6. Changed enum for WrapMode:

PyQt5:

self.texture.setWrapMode(QOpenGLTexture.ClampToEdge)

PyQt6:

self.texture.setWrapMode(QOpenGLTexture.WrapMode.ClampToEdge)

7. Changed enum to set application attributes:

PyQt5:

QApplication.setAttribute(Qt.AA_UseDesktopOpenGL)

PyQt6:

QApplication.setAttribute(Qt.ApplicationAttribute.AA_UseDesktopOpenGL)

A few basic non-graphical changes:

1. Changed enum for file open mode:

PyQt5:

file = QFile(path)
if not file.open(QIODevice.ReadOnly):
    print("Failed to open the file: " + path)

PyQt6:

file = QFile(path)
if not file.open(QIODevice.OpenModeFlag.ReadOnly):
    print("Failed to open the file: " + path)

2. The QApplication.exec_() method has been renamed to QApplication.exec()

PyQt5:

import sys
from PyQt5.QtWidgets import QApplication

app = QApplication(sys.argv)
sys.exit(app.exec_())

PyQt6:

import sys
from PyQt6.QtWidgets import QApplication

app = QApplication(sys.argv)
sys.exit(app.exec())

Falling Collada Cube with Bullet Physics, OpenGL 3.3:

• PyQt6: https://github.com/8Observer8/falling-collada-cube-bullet-physics-opengl33-pyqt6
• PySide6: https://github.com/8Observer8/falling-collada-cube-bullet-physics-opengl33-pyside6

You should install these packages:

• pip install PyQt6 (or PySide6)
• pip install PyOpenGL
• pip install numpy
• pip install Panda3D (for Bullet Physics)