QOpenGLWidget show black screen

Question

I tried the QOpenGLWidget example described here: https://stackoverflow.com/a/31524956/4564882

but I get only a black widget. The code is exactly the same. this the code

Answer 1

The problem was because I use Qt5 binaries built with the default configuration. The default in Qt 5.5 is "dynamic" GL -- both ANGLE (ES2)

ANGLE ((Almost Native Graphics Layer Engine) is an open source project by Google. Its aim is to map OpenGL ES 2.0 API calls to DirectX 9 API.)

and Desktop backends (Desktop OpenGL)are built, the decision on which one to use is taken at runtime.

The problem is that ANGLE only supports OpenGL>3.x, so the first code that I test is deprecated and not supported by ANGLE. The second is supported, that's why it worked.

So, I rebuild Qt to target Desktop OpenGL only to support my deprecated code, using:

configure -debug-and-release -opensource -opengl desktop -platform win32-msvc2015

and then run nmake, link my application to the new binaries, and my code works well!

Answer 2

In my case, my laptop uses NVIDIA external graphics card. So I went to NVIDIA Control Panel -> Manage 3D Settings -> Program Settings, and then selected "high-performance" for the .EXE file. This worked.

Answer 3

I had a black screen on desktop. I solved the problem by adding this line of code:

QCoreApplication::setAttribute(Qt::AA_UseDesktopOpenGL);

For example, put it here:

#include "widget.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_UseDesktopOpenGL);
    QApplication a(argc, argv);
    Widget w;
    w.show();
    return a.exec();
}