QT & raw OpenGL with glew not working

Row_Rebel

It's been 2 days now that I'm trying to setup a working window where I can issue raw openGL commands with glew, but all I can see on screen is just a white empty window while my glClearColor is set to red

So here's glwindow.h :

#ifndef GLWINDOW_H
#define GLWINDOW_H
#include <QWindow>
#include <QOpenGLContext>

class GLWindow : public QWindow {
    QOpenGLContext* context;

    public:
    GLWindow(const QSurfaceFormat& format);

    void initGL();
    void resize(int w, int h);
};
#endif // GLWINDOW_H

glwindow.cpp:

#define GLEW_STATIC
#include <glew.h>
#include "glwindow.h"
#include <QDebug>

GLWindow::GLWindow(const QSurfaceFormat& format) : context(0) {
    
    setSurfaceType( OpenGLSurface );
    setFormat(format);
    create();

    context = new QOpenGLContext(this);
    context->setFormat(format);
    context->create();

    context->makeCurrent(this);
            glViewport(0,0,500,500);
            glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
            glClear(GL_COLOR_BUFFER_BIT);
    context->swapBuffers(this);
}
void GLWindow::resize(int w, int h) { }
void GLWindow::initGL() { }

main.cpp:

#include <QGuiApplication>
#include <glwindow.h>
#include <QSurfaceFormat>
int main(int argc, char *argv[])
{
    QGuiApplication a(argc, argv);
    QSurfaceFormat format;
    format.setMajorVersion( 3 );

    #if !defined(Q_OS_MAC)
    format.setMinorVersion( 3 );
    #else
    format.setMinorVersion( 2 );
    #endif
    format.setDepthBufferSize( 24 );
    format.setSamples( 4 );
    format.setProfile( QSurfaceFormat::CoreProfile );

    GLWindow window(format);
    window.show();
    return a.exec();
}

Lastly here's the .pro file:

QT       += core gui 
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = Tentativo5
TEMPLATE = app
SOURCES += main.cpp\
    glwindow.cpp

HEADERS  += \
    glwindow.h
INCLUDEPATH += "C:/....../OpenGL/headers/GL"
LIBS += "C:/......./OpenGL/lib/glew32s.lib"
LIBS += opengl32.lib

I'm pretty desperate at this point so feel free to ask anything about the setup, I'm really not suited to set all the mess that qt apparently need to have a working opengl window

SGaist

Hi and welcome to devnet,

With Qt 5 you don't need glew at all, you can use QOpenGLFunctions and derived class.

Row_Rebel

@SGaist
Is there a step-bystep tutorial that explains them without too much magic?
Maybe ending up with a simple openGL window up and running

PS: Possibly without using QGLWidget since performance-wise seems not to be the best solution

SGaist

The OpenGL window example might be a good starting point.

Row_Rebel

@SGaist
Unfortunately I didn't understand many of the called functions in there like the need of exposeEvent or renderlater which was what I was referring before as "magic"

SGaist

renderLater is used to trigger an update of the scene while exposeEvent will trigger it when the window exposure changed.

Row_Rebel

@SGaist
Last question, I found a working example here: https://wiki.qt.io/Using-QOpenGLFunctions-and-QOpenGLContext
which I blindly implemented and played a bit around till I finally rendered a triangle on screen, the problem is that as with QGLWidget, if I resize fast enough I start to see white flickering as shown in this screenshot: http://oi63.tinypic.com/11wgi9t.jpg
what could be causing it?

Fun thing is that I switched from qglwidget since I thought the performance impact could have caused it

SGaist

I can't say from the top of my head. However, QGLWidget is old tech, you should move to the new QOpenGLWidget class directly.

Row_Rebel

@SGaist
Ok I guess i'll open a different question for this issue, thanks anyway for your help