QGLWidget renders black

[jonasbalmer]

I'm fairly new to Qt. I'm trying to make a custom VJ application. For my video-output I want to use OpenGL, which I control by another mainwindow. The problem is, It just renders black. I copypasted what the NeHe tutorial says for drawing a simple white triangle and rectangle, but it's still black. I don't get what's wrong with it. Is there anything I missed?
this is my glscreen.h

#ifndef GLSCREEN_H
#define GLSCREEN_H
 
#include <QMainWindow>
#include <QGLWidget>
 
class VJOutput : public QGLWidget{
    Q_OBJECT
public:
    VJOutput();
protected:
    void initializeGL();
    void paintGL();
    void resizeGL(int w, int h);
public slots:
    void Herteken();
 
};
 
 
#endif // GLSCREEN_H

#ifndef GLSCREEN_H
#define GLSCREEN_H

#include <QMainWindow>
#include <QGLWidget>

class VJOutput : public QGLWidget{
    Q_OBJECT
public:
    VJOutput();
protected:
    void initializeGL();
    void paintGL();
    void resizeGL(int w, int h);
public slots:
    void Herteken();

};


#endif // GLSCREEN_H

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here's the glscreen.cpp code

#include "glscreen.h"
#include "ui_glscreen.h"
#include <iostream>
#include <QTimer>
#include <math.h>
 
void VJOutput::initializeGL(){
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);		// Clear The Screen And The Depth Buffer
    glLoadIdentity();						// Reset The View
}
VJOutput::VJOutput(){
    initializeGL();
    QTimer *RedrawTimer = new QTimer(this);
    connect(RedrawTimer,SIGNAL(timeout()),this,SLOT(Herteken()));
    RedrawTimer->start(20);
 
}
void VJOutput::resizeGL(int w, int h){
 
}
 
void VJOutput::paintGL(){
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
 
    glTranslatef(-1.5f,0.0f,-6.0f);
 
    glBegin(GL_TRIANGLES);
      glVertex3f( 0.0f, 1.0f, 0.0f);
      glVertex3f(-1.0f,-1.0f, 0.0f);
      glVertex3f( 1.0f,-1.0f, 0.0f);
    glEnd();
 
    glTranslatef(3.0f,0.0f,0.0f);
 
    glBegin(GL_QUADS);
      glVertex3f(-1.0f, 1.0f, 0.0f);
      glVertex3f( 1.0f, 1.0f, 0.0f);
      glVertex3f( 1.0f,-1.0f, 0.0f);
      glVertex3f(-1.0f,-1.0f, 0.0f);
    glEnd();
}
void VJOutput::Herteken(){
    updateGL();
}

#include "glscreen.h"
#include "ui_glscreen.h"
#include <iostream>
#include <QTimer>
#include <math.h>

void VJOutput::initializeGL(){
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);		// Clear The Screen And The Depth Buffer
    glLoadIdentity();						// Reset The View
}
VJOutput::VJOutput(){
    initializeGL();
    QTimer *RedrawTimer = new QTimer(this);
    connect(RedrawTimer,SIGNAL(timeout()),this,SLOT(Herteken()));
    RedrawTimer->start(20);

}
void VJOutput::resizeGL(int w, int h){

}

void VJOutput::paintGL(){
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();

    glTranslatef(-1.5f,0.0f,-6.0f);

    glBegin(GL_TRIANGLES);
      glVertex3f( 0.0f, 1.0f, 0.0f);
      glVertex3f(-1.0f,-1.0f, 0.0f);
      glVertex3f( 1.0f,-1.0f, 0.0f);
    glEnd();

    glTranslatef(3.0f,0.0f,0.0f);

    glBegin(GL_QUADS);
      glVertex3f(-1.0f, 1.0f, 0.0f);
      glVertex3f( 1.0f, 1.0f, 0.0f);
      glVertex3f( 1.0f,-1.0f, 0.0f);
      glVertex3f(-1.0f,-1.0f, 0.0f);
    glEnd();
}
void VJOutput::Herteken(){
    updateGL();
}

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my VJ.pro file has:

# -------------------------------------------------
# Project created by QtCreator 2010-01-15T13:07:06
# -------------------------------------------------
QT += network \
    opengl \
    sql \
    xml \
    xmlpatterns \
    phonon \
    dbus
CONFIG += thread
TARGET = VJ
TEMPLATE = app
SOURCES += main.cpp \
    mainwindow.cpp \
    lib/Rhythm.cpp \
    lib/MidiDevices.cpp \
    lib/RtMidi.cpp \
    visualLib/glscreen.cpp
HEADERS += mainwindow.h \
    lib/Rhythm.h \
    lib/MidiDevices.h \
    lib/RtMidi.h \
    lib/RtError.h \
    visualLib/glscreen.h
LIBS += -L/alsa/ \
    -lasound \
    -lpthread
FORMS += mainwindow.ui

# -------------------------------------------------
# Project created by QtCreator 2010-01-15T13:07:06
# -------------------------------------------------
QT += network \
    opengl \
    sql \
    xml \
    xmlpatterns \
    phonon \
    dbus
CONFIG += thread
TARGET = VJ
TEMPLATE = app
SOURCES += main.cpp \
    mainwindow.cpp \
    lib/Rhythm.cpp \
    lib/MidiDevices.cpp \
    lib/RtMidi.cpp \
    visualLib/glscreen.cpp
HEADERS += mainwindow.h \
    lib/Rhythm.h \
    lib/MidiDevices.h \
    lib/RtMidi.h \
    lib/RtError.h \
    visualLib/glscreen.h
LIBS += -L/alsa/ \
    -lasound \
    -lpthread
FORMS += mainwindow.ui

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I'm using ubuntu and Qt Creator

[wysota]

Are you sure you shouldn't put anything inside resizeGL() or one of other GL methods to setup the projection (or some other, I'm not a GL expert) matrix?

[jonasbalmer]

you're right.
With the addition of this code it works:

void VJOutput::resizeGL(int w, int h){
    if (h==0)								// Prevent A Divide By Zero By
    {
            h=1;							// Making Height Equal One
    }
 
    glViewport(0, 0, w, h);					// Reset The Current Viewport
    glMatrixMode(GL_PROJECTION);						// Select The Projection Matrix
    glLoadIdentity();							// Reset The Projection Matrix
 
    // Calculate The Aspect Ratio Of The Window
    gluPerspective(45.0f,(GLfloat)w/(GLfloat)h,0.1f,100.0f);
 
    glMatrixMode(GL_MODELVIEW);						// Select The Modelview Matrix
    glLoadIdentity();							// Reset The Modelview Matrix
}

void VJOutput::resizeGL(int w, int h){
    if (h==0)								// Prevent A Divide By Zero By
    {
            h=1;							// Making Height Equal One
    }

    glViewport(0, 0, w, h);					// Reset The Current Viewport
    glMatrixMode(GL_PROJECTION);						// Select The Projection Matrix
    glLoadIdentity();							// Reset The Projection Matrix

    // Calculate The Aspect Ratio Of The Window
    gluPerspective(45.0f,(GLfloat)w/(GLfloat)h,0.1f,100.0f);

    glMatrixMode(GL_MODELVIEW);						// Select The Modelview Matrix
    glLoadIdentity();							// Reset The Modelview Matrix
}

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Thanks!