Qt OpenGL error '_imp_gl...'

Trying to learn how to use QGLWidget, but already so much time wasted handling these errors. I dont even understand them. I googled, but nothing. Please, any suggestions?

Code: https://gist.github.com/anonymous/77c57fde631c77810775

In function `ZN6Widget12initializeGLEv':
 undefined reference to `_imp__glEnable@4'
 undefined reference to `_imp__glShadeModel@4'
 and more...

You're not linking against any GL library.

Since Qt 5.5, on Windows, by default, Qt does not link against libGL, but has a runtime mechanism for deciding to load either libGL or ANGLE (depending on your OS capabilities). This means you can't just use glFoo -- you will get linking errors.

---

Solution: go through function resolvers, for instance QOpenGLFunctions:

QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();
f->glEnable(GL_FOOBAR);
f->glDrawArrays(...);

Note that on Windows you need function resolvers anyhow to use any OpenGL function introduced after 1.1.

Also, if you're using ES2-only or Desktop GL-only functions, you should force Qt to load the right GL implementation:

int main(int argc, char **argv) {
    // *before* creating it
    QApplication::setAttribute(Qt::AA_UseDesktopOpenGL);
    QApplication app(argc, argv); 

More info here.

_{(More radical solution: recompile Qt passing -opengl desktop or -opengl es2 to configure).}