# OpenGL [SOLVED] Depth buffer problem

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Hello,

I'm nowadays developping a game using OpenGL.

I tried so hard to fix my depth buffer problem, but i can't do anything about that ;

Here is the screenshot of the game, without the problem (my boxes' depth are very low) :

Now, if i put some depth on my boxes...

(For those who would like an animation, i recorded the problem there :

Well, I paste some of my code, tell me if i'm doing something wrong. (Well, I guess I do...)

// Init functionvoid init (){    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);    glEnable(GL_DEPTH_TEST);}// Drawing routinevoid draw (){    glClearColor(0.1, 0.1, 0.1, 1.0);    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gl_plateau_draw(gc->glPlateau);    glutSwapBuffers();}

Can you help me ?
If you need more code, I can copy / paste there.

Thank you ! :)

EDIT :
Oh ... I just noticed that switch
glEnable(GL_DEPTH_TEST);
and the
glutInitDisplayMode
was doing something better ...

There is still something wrong in the drawing of my boxes ; Sometimes my boxes are filled, sometimes not. (depends of the position of the camera)

[Edited by - Spl3en on October 19, 2010 2:41:38 PM]

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Try glDisable(GL_CULL_FACE). Polygons have a front and back side, and back-facing polygons are commonly culled away. Usually this is a good thing, and if you order your vertices correctly you will still get the correct behavior, unless you need to be able to view the same polygon from both directions.

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Thank you for the reply Erik, it's really appreciated :)

I didn't touch at culling anywhere else.

I still believe that it is a depth buffer problem :
As you can see, my tokens are visible, like if the boxes were invisible...

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Post the whole code.

Between
[source] and [/source]

Any what is the "depth range" and the "depth func"?

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Also try putting glEnable(GL_DEPTH_TEST); in your draw function.

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Quote:
 Also try putting glEnable(GL_DEPTH_TEST); in your draw function.

Thank you again for the advice, I didn't try this.
It seems to resolve the transparency problem, but it now does the same problem as the begginning... :-(

This one : Screenshot

Quote:
 Post the whole code.

Well, this is a school project, the whole source code length is almost 100ko (but only 20ko of OpenGL), so I uploaded this to Megaupload...
The files where I use openGL are prefixed by "Gl", and my draw routine is in GraphicContext.c.

I don't have so much hope that someone will analyze all my code to find the problem, but if someone do, be sure that someone in the world will thank you very very much :)

Quote:
 Any what is the "depth range" and the "depth func"?

I'm not sure of the meaning of your question, but i use that :
gluPerspective(30, width/height, 0.1, 10000);

I don't know how to use glDepthRange(), maybe that is the problem ?

EDIT :
I got a function to set the FPS to 60, the rendering changes if i modify the value of the max FPS ... I guess i'm doing wrong with the depth buffer and the FPS.

EDIT 2 :
Erm, i removed the FPS max value, and it didn't change anything, so it is surelly not that... :(

[Edited by - Spl3en on October 19, 2010 2:49:37 PM]

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Um... how about looking at the documentation? If you google those functions I'm positive you can find the necessary info about them.

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I'm sorry, english is not my native language, so I sometimes get some problems to understand exactly the documentation...
Anyway, I just found the problem in the OpenGL FAQ, "12.040 Depth buffering seems to work, but polygons seem to bleed through polygons that are in front of them. What's going on?"...

I changed my zNear and ZFar to 100.0 / 10000.0, and it finally works :)

I still don't perfectly understand the mechanisms of zNear and zFar, but now I know the problem, I'm going to try to understand more documentation about these variables.

Thank you very much szecs and Erik Rufelt !
I increased your user rating :)

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Quote:
 Original post by Spl3enI changed my zNear and ZFar to 100.0 / 10000.0, and it finally works :)I still don't perfectly understand the mechanisms of zNear and zFar, but now I know the problem, I'm going to try to understand more documentation about these variables.

The depth-buffer has limited precision, so if zNear is too small or zFar too large, then there are not enough bits to keep track of the possible depth values with high enough precision.
Since you get such large problems I suspect your depth-buffer is only 16 bits, where you probably want 24. I'm not sure how to specify the desired precision using GLUT though.
You can check the precision with:
GLint depthBits;glGetIntegerv(GL_DEPTH_BITS, &depthBits);

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You are perfectly right Erik, glGetIntegerv(GL_DEPTH_BITS, &depthBits) returns 16 to me.
Well, I keep it in mind, 16-bits seems to be enough for the moment, I'm not planning to draw a background in my application for the moment.

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