disappearing quad

OpenGL OpenGL: Basic Coding
1

I have a very large quad with a weather texture on it to represent my sky. When I move around in my scene the quad disappears when i rotate my camera(most angles). When I say disappear I mean that the quad gradually fades away as I rotate my camera.

One thing I’ve noticed is that it may be a graphic card specific problem. The quad is visible all the time on my Geforce4 TI4600, but not on Geforce2mx or a ATI card we bought recently. It’s seem it’s visible on all Geforce4 based cards, but not allways becuse on one machine we have a Geforce4 and a Geforce2 installed(we needed 3 monitors), and the same problem was apparent there(on all monitors).

Does anybody have a clue on this one?

2

Do you have fog disabled?

3

what is your far clipping plane?

4

Fog is enabled and far clip is 10000

5

Are you billboarding your quad? (Drawing it so that it always faces you).

Do you have anything other than glFrustum/gluPerspective or glOrtho/gluOrtho2d in the PROJECTION matrix? (e.g. you don’t do a gluLookAt/glTranslate/glRotate/glScale in the PROJECTION matrix, right? You do them in the MODELVIEW where they belong?)

[This message has been edited by Deiussum (edited 08-07-2003).]

6

I’m not billboarding my quad. It’s positioned right above where I start +500 in y direction. The quad does not move when I move around. It’s more like it fades gradually away at most angles. Mostly I only see the background color.

7

What are your light settings, are your normals being calculated correctly?

8

…does the problem go away when you turn off fog?

9

I turned of fog, and then my quad became visible all the time. Why is that? I want the fog on to get smooth transition where my far clip ends(example: far clip 10000, linear fog 8000 to 10000).

10

Read Deiussum’s post again.
You must do your camera work in the modelview matrix or fog will break.

[This message has been edited by Relic (edited 08-08-2003).]

11

All my camera work is done in the right place. What do you mean by “fog will break”?

12

You say you put your camera work in the “right place” but the symptoms say otherwise. Perhaps question 8.100 of the Technical FAQ can help.

In short, putting anything like gluLookAt, glTranslate, glRotate, or glScale in the PROJECTION matrix will muck up calcualtions for lighting and fog, both of which do calculations based on the MODELVIEW matrix.

[This message has been edited by Deiussum (edited 08-08-2003).]

13

It seems that the quad is not “fading” away as I first thought. When I moved my camera above my quad, then looking down on my terrain, I saw that the quad did not disappear, but the texture was getting the the same color as my background color(except for where my texture is transparent). At some angles the quad is getting it’s correct colors. Maybe this info will tell somebody what is wrong?