CODEWITHSUNDEEP
c++cqtopengl
Krab
Krab

Reputation: 6756

OpenGL "black screen" frustration

I am still trying to figure out, why i see only typical "black screen". I render just one rectangle, but nothing happened.

#include "expwidget.h"
#include <iostream>

ExpWidget::ExpWidget(QObject *parent) :
    QGLWidget(QGLFormat(QGL::DoubleBuffer), (QWidget *) parent)
{

    QGLFormat fmt = this->format();
    fmt.setDepth(true);

    this->setFormat(fmt);
}



void ExpWidget::initializeGL() {

    QGLWidget::initializeGL(); 

    std::cout << "inicializace...\n";

    glClearColor(0.0f,0.0f,0.0f,0.0f);

    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);
    glDisable(GL_LIGHTING);

}


void ExpWidget::paintGL() {

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity();

    glColor3f(1, 0, .5);
    glBegin(GL_QUADS);
        glVertex3f(-1.0f,-1.0f,-5.0f);
        glVertex3f(1.0f,-1.0f,-5.0f);
        glVertex3f(1.0f,1.0f,-5.0f);
        glVertex3f(-1.0f,1.0f,-5.0f);
    glEnd();

    glFlush();


}

void ExpWidget::resizeGL(int w, int h) {

    glViewport(0, 0, w, h);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    glFrustum(-2.0, 2.0, -2.0, 2.0, 0.0, -30.0);

    glMatrixMode(GL_MODELVIEW);


}

Upvotes: 0

Views: 1841

Answers (2)

DiJuMx
DiJuMx

Reputation: 524

I've faced a similar problem in the past, but I don't claim to be an expert.

Calls to glFrustum are in the form glFrustum(left, right, bottom, top, near, far)

near and far must both be positive and non-zero. (http://www.opengl.org/sdk/docs/man2/xhtml/glFrustum.xml)

so in your case I would recommend changing your call to:

glFrustum(-2.0, 2.0, -2.0, 2.0, 1.0, 30.0);

Also, your coordinates should have negative Z to render in this view.

Upvotes: 2

catscradle
catscradle

Reputation: 1719

http://www.opengl.org/sdk/docs/man2/xhtml/glFrustum.xml:

nearVal, farVal

Specify the distances to the near and far depth clipping planes. Both distances must be positive.

Upvotes: 1

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