Qml font rendering bug due to glCullFace(GL_FRONT)

We are using Qml to build an OpenGL program. We share the same opengl context with Qt.

During our rendering, we set glCullFace(GL_FRONT), and call QQuickWindow::resetOpenGLState() after our rendering.

Then occasionally, Qt renders the fonts incorrectly.

Currently we get around this problem by calling glCullFace(GL_BACK) after our rendering.

Since the fonts are rendered correctly sometimes, we think there exists a call to glCullFace(GL_BACK) somewhere in the Qt rendering code path. But that is not guaranteed to be run. So we suggest to add glCullFace(GL_BACK) to QQuickWindow::resetOpenGLState() to ensure that Qt renders fonts correctly.

And another API might also need to be reset: glClipControl()