help w/ adjusting viewing volume

OpenGL Development JOGL Development
#1

I’ve got something wrong with I think my viewing volume. Specifically, when I zoom in (done using glScale in my orthographic projection), I can see my objects being clipped on the front most edge until it disappears and what I’m trying to do is produce an effect that makes it look I’m magnifying into the object so I can view the surfaces or just a few of the polygons. Problem is, the leading most edges of my object start to get clipped so that when I’m looking into it, I see nothing.

Since I’m new to all this, I’m guessing it’s as if I need to fix my front plane on my viewport (the back one too cause it clips the rear of my object when I rotate it), but so far, no luck.

Any help much appreciated.

#2

If you’re using gluOrtho2D to set up your orthographic projection, it is setting up the near and far clipping planes to -1 and 1, respectively. Look at the implementation of gluOrtho2D in src/net/java/games/jogl/impl/Project.java:

public void gluOrtho2D(GL gl, double left, double right, double bottom, double top) {
  gl.glOrtho(left, right, bottom, top, -1, 1);
}

You probably need to adjust these.

#3

You probably need to adjust the near and far clipping planes dynamically to make sure your objects are contained in the viewing volume. As you zoom in your near plane should be backed up (larger negative numbers) and your far plane should be moved out (larger positive numbers).

#4

[quote]If I’m zooming in, the object is being scaled larger, and if the near plane is being backed up (meaning going down the z-axis, negative) … the near plane will just run into the front leading edges of my object and clip it … am I right? Isn’t this front near pane also the view port?
[/quote]
The near plane probably has to be a more negative value than any Z coordinate of any triangle in your model. I haven’t used orthographic projections much but I assume they work pretty much as perspective projections where you are supposed to fit the viewing volume (in particular, the near/far clipping planes) as tightly to your model as possible to ensure you get good precision for your z-buffer.