Question

I’m working on an OpenGL example out of a Qt programming book. Almost everything works fine, but the default scale seems to be way off. I should be seeing a pretty standard cube, but instead I see this.

My code for the cube looks like this:

glBegin(GL_QUADS);

//top face
qglColor(m_faceColors[0]);
glVertex3f(-m_cubeSize, m_cubeSize, -m_cubeSize);
glVertex3f(m_cubeSize, m_cubeSize, -m_cubeSize);
glVertex3f(m_cubeSize, m_cubeSize, m_cubeSize);
glVertex3f(-m_cubeSize, m_cubeSize, m_cubeSize);

// left face
qglColor(m_faceColors[1]);
glVertex3f(-m_cubeSize, -m_cubeSize, -m_cubeSize);
glVertex3f(-m_cubeSize, m_cubeSize, -m_cubeSize);
glVertex3f(-m_cubeSize, m_cubeSize, m_cubeSize);
glVertex3f(-m_cubeSize, -m_cubeSize, m_cubeSize);

And so on…

I’m not calling any weird glScalef’s. My resizeGL() looks like this:

void GLWidget::resizeGL(int width, int height)
{
    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    m_width = (height>0) ? (GLfloat)width/height : 1;
    glOrtho(-width, +width, -1.0, 1.0, -2, 2);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

m_cubeSize is 1.0

Anyway, when I do this in the draw() function:

glScalef(275, 0.5, 0.5);

I see this (looks correct):

Does anyone know why the x scale would be so small by default? I’m doing exactly what the book says, but I’m really confused. I’ve done quite a bit of OpenGL before (with Glut), but this is my first time using Qt as a wrapper.

Answer 1

What exactly do you expect this:

glOrtho(-width, +width, -1.0, 1.0, -2, 2);

to do? Wouldn’t it make more sense to do something like this:

glOrtho(-width, +width, -height, height, -2, 2);