OpenGL: GL_QUADS does not draw square

Question

I'm trying to draw a square on the screen but it clearly draws a rectangle.

This is my render code:

glClear(GL_COLOR_BUFFER_BIT);
glTranslatef(0,0,-0.1);
glBegin(GL_QUADS);
    glVertex3f(0,0,0);
    glVertex3f(1,0,0);
    glVertex3f(1,1,0);
    glVertex3f(0,1,0);
glEnd();

SDL_GL_SwapBuffers();

And OpenGL Init code:

glClearColor(0,0,0,0.6f);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(30,640.0/480.0,.3f,200.0);
glMatrixMode(GL_MODELVIEW);

Why is this happening?

Answer 1

I don't see anywhere in your code where you have set-up the glViewport. I will rather write something like this in your init method:

glViewport(0,0,640,480);        // Reset The Current Viewport

glMatrixMode(GL_PROJECTION);    // Select The Projection Matrix
glLoadIdentity();               // Reset The Projection Matrix

// Calculate The Aspect Ratio Of The Window
gluPerspective(30.0f,(GLfloat)640/(GLfloat)480,0.3f,200.0f);

glMatrixMode(GL_MODELVIEW);     // Select The Modelview Matrix
glLoadIdentity();       

also check the second Nehe tutorial it will help you to start with OpenGL for very basic stuff like drawing primitives such as triangle, square etc...

Answer 2

Try using gluOrtho2D to generate a correct orthogonal projection matrix, in your case gluOrtho2D(0,640,0,480), this is assuming you want a square in 2D and not 3D.

This will of course change your coordinate system from (0,1),(0,1) to (0,640),(0,480).