PaintGL() doesn't work



  • i want to run opengl in Qt and i used QGLWidget to do this but it doesn't work.

    here is my code:
    @
    #include <QGLWidget>

    class GLWidget : public QGLWidget
    {
    Q_OBJECT
    public:
    explicit GLWidget(QWidget *parent = 0);

    virtual void initializeGL();
    virtual void resizeGL(int w, int h);
    virtual void paintGL();
    

    };
    @

    @
    #include "glwidget.h"
    #include <gl/glut.h>

    GLWidget::GLWidget(QWidget *parent) :
    QGLWidget(parent)
    {}

    void GLWidget::initializeGL()
    {
    setGeometry(300, 150, 640, 480);
    glShadeModel(GL_FLAT);
    glClearColor(0.5, 1.0, 0.2, 0);
    glClearDepth(1.0);
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
    }

    void GLWidget::resizeGL(int w, int h)
    {
    if(0 == h)
    h = 1;
    glViewport(0, 0, (GLint)w, (GLint)h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    // gluPerspective(45.0, (GLfloat)width/(GLfloat)height, 0.1, 100.0);
    //glMatirxMode(GL_MODELVIEW);
    glLoadIdentity();
    }

    void GLWidget::paintGL()
    {
    //qglClearColor(QColor(0,0,255,128));
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glColor3f(0.0, 0.0, 1.0);
    glBegin(GL_TRIANGLES);
    glVertex3f(0.0,1.0,0.0);
    glVertex3f(-1.0,-1.0,0.0);
    glVertex3f(1.0,-1.0,0.0);
    glEnd();
    }
    @

    @
    int main(int argc, char *argv[])
    {
    QApplication a(argc, argv);

    GLWidget *gl = new GLWidget();
    gl->updateGL();
    gl->show();
    
    return a.exec&#40;&#41;;
    

    }
    @

    it seems that the fonction initializeGL works because the color of background changes. but i cant see my triangle.
    could someone help me plz???



  • by the way, the version of my qt is 5.0.2


  • Moderators

    The background color is set by the glClear() call, not glClearColor(), so your paintGL() does work.

    Btw. "doesn't work" is not very descriptive.

    You didn't set a proper transformation matrix and you draw at depth 0.0 so your triangle falls outside of the view frustum.

    For drawing a flat 2D triangle you can try this:
    @
    void GLWidget::resizeGL(int w, int h) {
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-1, 1, -1, 1, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    }

    void GLWidget::paintGL() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor3f(0.0, 0.0, 1.0);
    glBegin(GL_TRIANGLES);
    glVertex2f(0.0,1.0);
    glVertex2f(-1.0,-1.0);
    glVertex2f(1.0,-1.0);
    glEnd();
    }
    @



  • thx. i copied ur two functions.
    but i cant still see the triangle...

    [quote author="Chris Kawa" date="1417448239"]The background color is set by the glClear() call, not glClearColor(), so your paintGL() does work.

    Btw. "doesn't work" is not very descriptive.

    You didn't set a proper transformation matrix and you draw at depth 0.0 so your triangle falls outside of the view frustum.

    For drawing a flat 2D triangle you can try this:
    @
    void GLWidget::resizeGL(int w, int h) {
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-1, 1, -1, 1, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    }

    void GLWidget::paintGL() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor3f(0.0, 0.0, 1.0);
    glBegin(GL_TRIANGLES);
    glVertex2f(0.0,1.0);
    glVertex2f(-1.0,-1.0);
    glVertex2f(1.0,-1.0);
    glEnd();
    }
    @[/quote]


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