Updating Window QTOpenGL

**xleniz** · 22nd February 2012, 20:09

Can someone help me, I need to update window in QTOpenGL ( if I press F10 I want to zoom, or change X or Y, but it doesnt update )

Qt Code:

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#include <QtGui/QApplication>
#include "mainwindow.h"
#include <QtOpenGL/QGLWidget>
#include <QtGui/QMouseEvent>
#include <GL/glu.h>
 
int cameraX, cameraY, cameraZ;
 
class GLWidget : public QGLWidget{
public:
    void initializeGL();
    void resizeGL(int w, int h);
    void paintGL();
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void keyPressEvent(QKeyEvent *event);
};
 
void GLWidget::initializeGL() {
    glDisable(GL_TEXTURE_2D);
    glDisable(GL_DEPTH_TEST);
    glDisable(GL_COLOR_MATERIAL);
    glEnable(GL_BLEND);
    glEnable(GL_POLYGON_SMOOTH);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glClearColor(3, 3, 3, 0);
    cameraX = 0;
    cameraY = 0;
    cameraZ = 0;
}
 
void GLWidget::resizeGL(int w, int h) {
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, w, 0, h); // set origin to bottom left corner
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
 
void GLWidget::paintGL() {
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(5,0,0);
    glTranslatef(cameraX, cameraY, cameraZ);
    glBegin(GL_POLYGON);
        glVertex2f(0,0);
        glVertex2f(0,500);
        glVertex2f(500,0);
    glEnd();
}
void GLWidget::mousePressEvent(QMouseEvent *event) {
 
}
void GLWidget::mouseMoveEvent(QMouseEvent *event) {
    printf("%d, %d\n", event->x(), event->y());
}
 
void GLWidget::keyPressEvent(QKeyEvent* event) {
    switch(event->key()) {
    case Qt::Key_Escape:
        close();
        break;
    case Qt::Key_F10:
        cameraX += 0.5f;
        break;
    default:
        event->ignore();
        break;
    }
}
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    GLWidget window;
    window.resizeGL(800, 600);
    window.show();
    a.exec();
}

#include <QtGui/QApplication>
#include "mainwindow.h"
#include <QtOpenGL/QGLWidget>
#include <QtGui/QMouseEvent>
#include <GL/glu.h>

int cameraX, cameraY, cameraZ;

class GLWidget : public QGLWidget{
public:
    void initializeGL();
    void resizeGL(int w, int h);
    void paintGL();
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void keyPressEvent(QKeyEvent *event);
};

void GLWidget::initializeGL() {
    glDisable(GL_TEXTURE_2D);
    glDisable(GL_DEPTH_TEST);
    glDisable(GL_COLOR_MATERIAL);
    glEnable(GL_BLEND);
    glEnable(GL_POLYGON_SMOOTH);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glClearColor(3, 3, 3, 0);
    cameraX = 0;
    cameraY = 0;
    cameraZ = 0;
}

void GLWidget::resizeGL(int w, int h) {
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0, w, 0, h); // set origin to bottom left corner
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void GLWidget::paintGL() {
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(5,0,0);
    glTranslatef(cameraX, cameraY, cameraZ);
    glBegin(GL_POLYGON);
        glVertex2f(0,0);
        glVertex2f(0,500);
        glVertex2f(500,0);
    glEnd();
}
void GLWidget::mousePressEvent(QMouseEvent *event) {

}
void GLWidget::mouseMoveEvent(QMouseEvent *event) {
    printf("%d, %d\n", event->x(), event->y());
}

void GLWidget::keyPressEvent(QKeyEvent* event) {
    switch(event->key()) {
    case Qt::Key_Escape:
        close();
        break;
    case Qt::Key_F10:
        cameraX += 0.5f;
        break;
    default:
        event->ignore();
        break;
    }
}
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    GLWidget window;
    window.resizeGL(800, 600);
    window.show();
    a.exec();
}

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Thanks!

**AlexSudnik** · 23rd February 2012, 08:03

Seems like you have to make the widget update ( re-draw ) itself. Try to call void QGLWidget::updateGL() after "cameraX += 0.5f;"

**xleniz** · 23rd February 2012, 13:36

Qt Code:

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cameraX += 0.5f;
QGLWidget::updateGL();

cameraX += 0.5f;
QGLWidget::updateGL();

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Doesn't work

**Talei** · 23rd February 2012, 14:15

Because

int cameraX, cameraY, cameraZ;

is not a camera. You simply update some int value and refresh view.

You need either transform projection matrix according to camerax or use gluLookAt().

Link to RTM

Basically this has nothing to do with Qt.

**AlexSudnik** · 23rd February 2012, 14:29

Ok , just curious : is GLWidget is the only widget in your application's GUI hierachy ? If so...well i'm more then sure that it's not , i'd suggest that you use...Grabber example^^. The thing is that if GLWidget has a parent , then keyPressEvent will be handled by it's parent , so in order to make your (child) widget to handle it you can either use event filters or...just to see if it works , use QCoreApplication::sendEvent method ( in your parent's keyPressEvent implementation ) , look at the docs or http://doc.qt.nokia.com/qq/qq11-events.html for more details on Qt's event system...

Eventually ,*not the best* solution may be :

Qt Code:

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void <GLWidget'sParentClass>::keyPressEvent(QKeyEvent *event)
{
 
 QCoreApplication::sendEvent( glWidget , event );
 
}

void <GLWidget'sParentClass>::keyPressEvent(QKeyEvent *event)
{

 QCoreApplication::sendEvent( glWidget , event );

}

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Your GLWidget::keyPressEvent(QKeyEvent* event) may be the same , but still you DO need to update it manually , otherwise it will only updated explicitly : when window will be resized etc.

**xleniz** · 23rd February 2012, 14:57

I got some error while declaring <void MainWindow>::keyPressEvent(QKeyEvent * event), I tried it in both main.cpp and mainwindow.cpp.

error:

Qt Code:

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/home/marcus/2-build-desktop/../2/mainwindow.cpp:16: error: â€˜voidâ€™ is not a template
/home/marcus/2-build-desktop/../2/mainwindow.cpp:16: error: explicit qualification in declaration of â€˜void keyPressEvent(QKeyEvent*)â€™
/home/marcus/2-build-desktop/../2/mainwindow.cpp:-1: In function â€˜void keyPressEvent(QKeyEvent*)â€™:
/home/marcus/2-build-desktop/../2/mainwindow.cpp:19: error: â€˜glWidgetâ€™ was not declared in this scope

/home/marcus/2-build-desktop/../2/mainwindow.cpp:16: error: â€˜voidâ€™ is not a template
/home/marcus/2-build-desktop/../2/mainwindow.cpp:16: error: explicit qualification in declaration of â€˜void keyPressEvent(QKeyEvent*)â€™
/home/marcus/2-build-desktop/../2/mainwindow.cpp:-1: In function â€˜void keyPressEvent(QKeyEvent*)â€™:
/home/marcus/2-build-desktop/../2/mainwindow.cpp:19: error: â€˜glWidgetâ€™ was not declared in this scope

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Here's main window if it's needed.

Qt Code:

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#include "mainwindow.h"
#include "ui_mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}
 
MainWindow::~MainWindow()
{
    delete ui;
}

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

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**AlexSudnik** · 23rd February 2012, 15:26

Did you just...copy-paste it ? ^^ Hm, i think you should step away from Qt for a while and learn native OOP / C++ programming , because you seem to be missing core moments:

void keyPressEvent(QKeyEvent *event) is a protected method : it's supposed to be reimplemented by the child classes . Aside from reimplementation , you've declared new public method with the same signature...So that was your initial problem (according to the code you've shared in the first post) . Now , you show another piece of code (seems like copy-pasted again^^) that doesn't seem to have anything related to your first program.

**xleniz** · 23rd February 2012, 15:29

Originally Posted by AlexSudnik

Did you just...copy-paste it ? ^^ Hm, i think you should step away from Qt for a while and learn native OOP / C++ programming , because you seem to be missing core moments:

void keyPressEvent(QKeyEvent *event) is a protected method : it's supposed to be reimplemented by the child classes . Aside from reimplementation , you've declared new public method with the same signature...So that was your initial problem (according to the code you've shared in the first post) . Now , you show another piece of code (seems like copy-pasted again^^) that doesn't seem to have anything related to your first program.

Heheh, yes, I had a hard time googling a QT OpenGL code, theres so few examples that I understand how to add.
You got a site ?? (maybe with .pro files)

**AlexSudnik** · 23rd February 2012, 15:35

What do you mean "googling a QT OpenGL code" ? There is a folder called "examples" in the Qt home dir.Navigate to "examples/opengl" folder...everything you need ( headers , sources and project files ) is there.

**xleniz** · 23rd February 2012, 18:01

Ok thanks, I downloaded SDK now, though I think I need a more simple openGL example.

Btw whats difference between Native and OpenGL? Native looks better on my computer.

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