Zoom bug - ZClip

[Bigboy]

Hi,

Id like to query the Newtek guys on the zoom+ZClip they get with openGL... They claim this is a feature+limit of open gl, but being an experienced graphics programmer, I'd like to ask just how they are going about this, as no one else I know has ever gotten this problem.

It "looks" like they are changing the camera field of view for ZOOM, rather than moving the camera in (translating). Can I ask why?

The ZClip is bloody annoying, and is the only limiting feature I found in another wise damn fine piece of software...

When doing a "SHIFT-A", this fixes the clip problem, this is because they have now moved the camera....so why not do this on ZOOM as well? Just move the camera down the current vector? I had a play, and I assume this is so they can zoom in, rotate, and zoom out but still be focused on the current point or something? I would argue there are other ways to do this without hitting the ZClip thing, scaling springs to.....?

Anyway...Just though Id ask..

[fxnut]

Originally posted by Bigboy
It "looks" like they are changing the camera field of view for ZOOM, rather than moving the camera in (translating). Can I ask why?

Are you talking about the Modeller 3D viewport? (I'm guessing you are, since you mentioned doing a Shift+A) Cause as far as I can tell, they're not changing the field of view at all, and they're just using the gluLookAt() function (or something which has a very similar result anyway). I don't get any clipping issues at all with the Modeller viewport.

But it does appear that they change the field of view for the standard perspective view in Layout. It's never bothered me though - if clipping becomes a problem then I just use the "[" and "]" keys to change the grid size. I've always found 3DStudio Max's implementation of perspective viewports hugely more unmanageable than Lightwave's. In the versions of Max that I've used, you sometimes get horrendous problems with depth sorting polygons and clipping.

Technically speaking though, changing the field of view is the "correct" thing to do when altering a zoom factor for a camera.

[Bigboy]

Sorry, I should have mentioned....Yes, Im speaking about Modeller perspective view, which I use a lot.

And sorry (again!), Im not saying that what they are doing is wrong, Im simply saying that you should be able to achive the same results approching it in another way, without hitting either GL or graphics card limits.

I agree that LW views are great to use, but whem Im dealing with large objects, I zoom in only to have the back end of it vanish... which is irritating. Im sure there is a "better method" to allow the ZClip to not be an issue.

[Bigboy]

Actually... Ive thought of another way (other than the scale)...

When you have your lookat locations, form a vector from the current eye, (you probably do anyway), then make it unit, and scale this - this is your ZOOM value. Then you just rotate this vector, and your eye will move around the scene (rather than ZOOM).

That way, you can still rotate and move back EXACTLY the same as you do now, but by moving down the current vector from say 0 to 1 (or -blah to +blah), you eliminate the ZClip totally...which would be nice.

Go on... you know you want to! :D



Smart Arse methods (c) Anti-ZClip lobby 2003