CODEWITHSUNDEEP
c++openglglut
Josh
Josh

Reputation: 12566

OpenGL - Perspective Issue

I just want to create a perspective where the eye of the camera would be, at, say: (2, 2, -2), looking right at the origin. I'm trying to use a combination of gluLookAt() and glFrustum(), but for some reason, though it is rendering, my objects look very distorted:

glMatrixMode( GL_PROJECTION );
glLoadIdentity();
glFrustum (-1.0, 1.0, -1.0, 1.0, 1.0, 500.0);

... 

gluLookAt (-2.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0, -1.0, 0.0);

What am I doing wrong?

EDIT: Here is a screenshot. The left side defines a profile curve to be swept around the y-axis. It should be a cylinder in the perspective view, but it's... warped.

enter image description here

EDIT 2: Also, those axis in the perspective view are set up as followed, which I know isn't correct:

// draw the axis
   glBegin(GL_LINES);
     // x
     glVertex3f(500.0, 0.0, 0.0);
     glVertex3f(-500.0, 0.0, 0.0);
     // y
     glVertex3f(0.0, -500.0, 0.0);
     glVertex3f(0.0, 500.0, 0.0);
     // z
     glVertex3f(0.0, 0.0, -500.0);
     glVertex3f(0.0, 0.0, 500.0);

   glEnd();

EDIT 3: Also, none of the vertices of that shape have an x, y, or z value greater than 1.0..

Upvotes: 1

Views: 584

Answers (2)

datenwolf
datenwolf

Reputation: 162307

What am I doing wrong?

I don't thing you're doing wrong anything. The kind of view you want to have in your left pane is usually done using a orthographic projection. The distortion you see is just a perspective distortion; you're not looking perpendicular onto the curve (the curve lies in the XY plane, and you're looking at the XY plane from some angle).

Side note:

The projection matrix only defines the "lens" of OpenGL. It must not be used to place the "camera". Any eyepoint positioning (the view) is defined as part of the modelview transformation. Thus gluLookAt is meant to be used on the modelview matrix.

Upvotes: 3

NickLH
NickLH

Reputation: 2645

Your frustum is set up as if the screen is square. If your screen isn't square this will distort the objects badly.

Also, if the objects are close to your camera, the near and far distances can affect the image.

And one more thing, your up axis in gluLookAt is pointing down.

Posting a screenshot would help identify the problem.

Upvotes: 0

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