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Asked: 2026-05-13T07:07:02+00:00

I have the following OpenGL code in the display function: glLoadIdentity(); gluLookAt(eyex, eyey, eyez,

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I have the following OpenGL code in the display function:

glLoadIdentity();
gluLookAt(eyex, eyey, eyez, atx, aty, atz, upx, upy, upz);
// called as: gluLookAt(20, 5, 5, -20, 5, 5, 0, 1, 0);

axis();
glutWireCube (1.);

glFlush ();

axis() draws lines from (0,0,0) to (10,0,0), (0,10,0) and (0,10,0), plus a line from (1,0,0) to (1,3,0).

My reshape function contains the following:

glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
gluPerspective(45.0, (GLsizei) w / (GLsizei) h, 1.0, 100.0);
glMatrixMode (GL_MODELVIEW);

This image shows the result of running the program with 1. as the argument to glutWireCube:

glutWireCube(1.)

As you can see, the cube isn’t centered around (0,0,0) as the documentation says it should be:

The cube is centered at the modeling
coordinates origin (…) (source)

If I run the program with 5. as the argument, the cube is displaced even further:

glutWireCube(5.)

Why is that, and how do I place the cubes around (0,0,0)?

FURTHER INFORMATION

It doesn’t matter if I switch the order of axis() and glutWireCube. Surrounding axis() with glPushMatrix() and glPopMatrix() doesn’t fix it either.

SOLUTION

I modified gluPerspective to start looking further away from the camera, and now the Z-buffering works properly, so it is clear that the cubes are placed around the origin.

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1 Answer

  1. Editorial Team

    Are you sure axis does not mess with the view matrix ?

    What happens if you call it after the drawing of the cube ?

    Edit to add:

    Actually… Looking at the picture closer, it looks like it might be centered at the origin.

    The center of the cube seems to align exactly with the intersection of the 3 axes. The only thing that looks suspicious is that the red line does not write over the white edge. do you have Z-buffering properly set up ?

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