How to update a OpenGL GLWidget embedded within QT?

**sonda** · 19th March 2013, 01:29

Hi everyone!
I am developing a really simple application using QT and OpenGL. The application contains a few buttons for interaction and a widget tab containing 3 pages, the first two for analysing and processing some data and the third contains a GLWidget which should draw the result points in a 3d space.
At the beginning the 3d space doesn't contain any points and after all the data are processed it should draw the 3 points.
So far I have tried to call an external function to paintGL() to draw a solid cube at the centre of the scene. The method is correctly called but the widget does not display any cube.
If you want I can post part of the code and if you have any questions then please do not hesitate to ask me.
I hope someone of you can help me with this.

**wysota** · 19th March 2013, 06:31

Just call update() on the widget.

**sonda** · 19th March 2013, 15:17

I have tried but it doesn't work, so I decided to post my code.

glwidget.cpp

Qt Code:

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GLWidget::GLWidget(QWidget *parent) :
    QGLWidget(parent)
{
    connect(&timer, SIGNAL(timeout()), this, SLOT(updateGL()));
    timer.start(1000);
}
 
void GLWidget::initializeGL(int w, int h) {
    glClearColor(0.2f, 0.2f, 0.2f, 1);
    glViewport(0, 0, w, h);
    // Setup light
    const GLfloat light_ambient[] = { 0.0f, 0.0f, 0.0f, 1.0f };
    const GLfloat light_diffuse[] = { 1.0f, 1.0f, 1.0f, 1.0f };
    const GLfloat light_specular[] = { 1.0f, 1.0f, 1.0f, 1.0f };
    const GLfloat light_position[] = {2.0f, 5.0f, 5.0f, 0.0f };
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);
    glEnable(GL_DOUBLE);
    glShadeModel(GL_SMOOTH);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_LIGHT0);
    glEnable(GL_LIGHTING);
    glEnable(GL_COLOR_MATERIAL);
    glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);
    glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);
    glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);
    glLightfv(GL_LIGHT0, GL_POSITION, light_position);
    glEnable(GL_CULL_FACE);
    glCullFace(GL_BACK);
    glDepthFunc(GL_LESS);
    glEnable(GL_COLOR_MATERIAL);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0, 1.0, 0.0001, 1000.0);
    glMatrixMode(GL_MODELVIEW);
    current_view= TOP_VIEW;
 
}
 
/ Display
void GLWidget::paintGL() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnable(GL_DEPTH_TEST);
    glLoadIdentity();
    setView();
    if (current_view == EXPLORING_VIEW)
        calculate_lookpoint();
    gluLookAt(eyex, eyey, eyez, centerx, centery, centerz, upx, upy, upz);
    // Draw axis and add points
    drawAxis();
    int ind;
    Skyline s;
    if (s.skylineGenerated()) {
        drawCube();
        cout << "Generated" << endl;
    }
   swapBuffers();
}
 
void GLWidget::drawCube(void){
    cout << "Drawn\n";
    glTranslatef(0.0,0.0,0.0);
    glColor3f(1.0,0.0,0.0);
    glutSolidCube(2.0);
    update();
}
 
// Reshape
void GLWidget::resizeGL(int w, int h) {
    glViewport(0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective (48.0, (GLfloat) w/(GLfloat) h, 10.0, 800.0);
    glMatrixMode (GL_MODELVIEW);
}

GLWidget::GLWidget(QWidget *parent) :
    QGLWidget(parent)
{
    connect(&timer, SIGNAL(timeout()), this, SLOT(updateGL()));
    timer.start(1000);
}

void GLWidget::initializeGL(int w, int h) {
    glClearColor(0.2f, 0.2f, 0.2f, 1);
    glViewport(0, 0, w, h);
    // Setup light
    const GLfloat light_ambient[] = { 0.0f, 0.0f, 0.0f, 1.0f };
    const GLfloat light_diffuse[] = { 1.0f, 1.0f, 1.0f, 1.0f };
    const GLfloat light_specular[] = { 1.0f, 1.0f, 1.0f, 1.0f };
    const GLfloat light_position[] = {2.0f, 5.0f, 5.0f, 0.0f };
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);
    glEnable(GL_DOUBLE);
    glShadeModel(GL_SMOOTH);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_LIGHT0);
    glEnable(GL_LIGHTING);
    glEnable(GL_COLOR_MATERIAL);
    glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);
    glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);
    glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);
    glLightfv(GL_LIGHT0, GL_POSITION, light_position);
    glEnable(GL_CULL_FACE);
    glCullFace(GL_BACK);
    glDepthFunc(GL_LESS);
    glEnable(GL_COLOR_MATERIAL);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0, 1.0, 0.0001, 1000.0);
    glMatrixMode(GL_MODELVIEW);
    current_view= TOP_VIEW;

}

/ Display
void GLWidget::paintGL() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnable(GL_DEPTH_TEST);
    glLoadIdentity();
    setView();
    if (current_view == EXPLORING_VIEW)
        calculate_lookpoint();
    gluLookAt(eyex, eyey, eyez, centerx, centery, centerz, upx, upy, upz);
    // Draw axis and add points
    drawAxis();
    int ind;
    Skyline s;
    if (s.skylineGenerated()) {
        drawCube();
        cout << "Generated" << endl;
    }
   swapBuffers();
}

void GLWidget::drawCube(void){
    cout << "Drawn\n";
    glTranslatef(0.0,0.0,0.0);
    glColor3f(1.0,0.0,0.0);
    glutSolidCube(2.0);
    update();
}

// Reshape
void GLWidget::resizeGL(int w, int h) {
    glViewport(0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective (48.0, (GLfloat) w/(GLfloat) h, 10.0, 800.0);
    glMatrixMode (GL_MODELVIEW);
}

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Despite the fact I call update(), when I click on the tab containing this widget no cube is shown. Furthermore the light is not working. Can you please help me? Ah I have the entire Opengl program in a class and everything is working but I don't understand why the GLWidget is not working like the original program.

**wysota** · 19th March 2013, 16:25

Your drawCube() doesn't make sense. If you want to draw something, you are supposed to call update() and draw what needs to be drawn in paintGL().

**sonda** · 19th March 2013, 16:35

I have modified the code for paintGL() but this time everything (axis and cube) is rotating:

Qt Code:

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void GLWidget::paintGL() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnable(GL_DEPTH_TEST);
    glLoadIdentity();
    setView();
    if (current_view == EXPLORING_VIEW)
        calculate_lookpoint();
    gluLookAt(eyex, eyey, eyez, centerx, centery, centerz, upx, upy, upz);
    // Draw axis and add points
    drawAxis();
    int ind;
    Skyline s;
    if (s.skylineGenerated()) {
       glPushMatrix();
       glTranslatef(0.0,0.0,0.0);
       glColor3f(1.0,0.0,0.0);
       glRotatef(0.5,1,0,1);
       glSolidCube(2.0);
    glPopMatrix();
    update();
    }
   swapBuffers();
}

void GLWidget::paintGL() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnable(GL_DEPTH_TEST);
    glLoadIdentity();
    setView();
    if (current_view == EXPLORING_VIEW)
        calculate_lookpoint();
    gluLookAt(eyex, eyey, eyez, centerx, centery, centerz, upx, upy, upz);
    // Draw axis and add points
    drawAxis();
    int ind;
    Skyline s;
    if (s.skylineGenerated()) {
       glPushMatrix();
       glTranslatef(0.0,0.0,0.0);
       glColor3f(1.0,0.0,0.0);
       glRotatef(0.5,1,0,1);
       glSolidCube(2.0);
    glPopMatrix();
    update();
    }
   swapBuffers();
}

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And why the light is not working?

**wysota** · 19th March 2013, 17:51

You are not supposed to be calling update() from within paintGL(). The latter will be called by Qt as a result of the call to the former. Have you gone through at least one Qt OpenGL example?

**sonda** · 19th March 2013, 18:21

Yes I have seen lots of examples. Anyway I have decided to use my original program and execute it within the GLWidget. So I added this line

Qt Code:

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void Sk::on_pushButton_clicked()
{
 
    process.start("/home/user/Desktop/Test");
 
}

void Sk::on_pushButton_clicked()
{

    process.start("/home/user/Desktop/Test");

}

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How can I display the external program within the GLWidget?

**wysota** · 19th March 2013, 18:25

Originally Posted by sonda

How can I display the external program within the GLWidget?

You can't.

**sonda** · 19th March 2013, 18:31

But I have read about QX11embedContainer, I have tried to include the library but it gives me an error. So the only way to run that executable is to use an external window???

**wysota** · 19th March 2013, 20:23

Originally Posted by sonda

But I have read about QX11embedContainer, I have tried to include the library but it gives me an error.

QX11EmbedContainer requires "the other application" to know how to embed itself into a given X window.

So the only way to run that executable is to use an external window???

Basically yes.

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