Hello, When I use both OpenGL rendering and QPainter calls in the paintGL function of a QOpenGLWidget class, I get an OpenGL error code (1282) when checking glGetError().
The painting still works, i.e. what I want to draw correctly appears on the screen. Also, this error code only appears on MacOSX. On Linux, it works fine. Should I be concerned about that error code? It does not feel good and I'm really thinking there should not be any error at all in the OpenGL rendering. I'm mainly concerned about this error, because I have a larger, more complex application where I use multiple QOpenGLWidgets and switch between them (through a QStackedLayout) and there the whole window 'flickers' and misbehaves (i.e. does not render correctly). It is hard to search for OpenGL errors in my larger application, because I always get this 1282 error code, like I get it in the simple example shown below. I made a minimal example, just creating and showing a widget derived from QOpenGLWidget in main(). The code is here: https://gist.github.com/anonymous/625e69dd61f0685c1cae625bdefbac74 In the widget, I reimplemented initializeGL, resizeGL, paintGL. The paintGL function looks like this: void paintGL() { qDebug() << "Error 1:" << glGetError(); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glBegin(GL_TRIANGLES); glColor3f(1.0f, 0.0, 0.0); glVertex3f(-0.5f, -0.5f, 0); glColor3f(0.0, 1.0f, 0.0); glVertex3f(0.5f, -0.5f, 0.0); glColor3f(0.0, 0.0, 1.0); glVertex3f(0.0, 0.5f, 0); glEnd(); QPainter p(this); p.setPen(Qt::red); p.drawLine(rect().topLeft(), rect().bottomRight()); qDebug() << "Error 2: " << glGetError(); } Strangely, the output I get is this: Error 1: 0 Error 2: 0 Error 1: 1282 Error 2: 0 Error 1: 1282 Error 2: 0 So the first time, no error happens but the second time, there is an error. When I comment out QPainter and its two calls, the error code is "gone" (always 0). But when I comment out the OpenGL calls but keep the QPainter statements, the error is still there. Do I miss something? Any ideas how to debug? Should I be concerned about that error code or should I just ignore it? Could it be (one of the) sources of my more substantial OpenGL errors in my larger application? I'm using Qt 5.7. And as I've said, it only seem to appear on MacOSX. Thanks for any feedback! Best, Jan
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