OpenGL 3D Polygon question

This is a discussion on OpenGL 3D Polygon question within the Game Programming forums, part of the General Programming Boards category; Currently, OpenGL has whichever part of the polygon drawn last, is on top. So in 3D, if I rotate this ...

  1. #1
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    OpenGL 3D Polygon question

    Currently, OpenGL has whichever part of the polygon drawn last, is on top.
    So in 3D, if I rotate this object so the part that was drawn last should be behind the part that was drawn first, the former still shows up on top of the latter.

    Is there any easy way to fix this so it always draws the part closer to the screen on top of the part farther from it when two parts overlap?

    Here's what I'm currently using to draw this shape:
    Code:
                glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
                glClear (GL_COLOR_BUFFER_BIT);
    
                glPushMatrix();
                glRotatef (xtheta, 1.0f, 0.0f, 0.0f);  
                glRotatef (ytheta, 0.0f, 1.0f, 0.0f);  
                glRotatef (ztheta, 0.0f, 0.0f, 1.0f); 
                
                glBegin(GL_POLYGON);
                glColor3f (0.0f, 0.0f, 1.0f); glVertex3d(0, 0, 0);
                glColor3f (0.0f, 0.5f, 1.0f);glVertex3d(.75, 0, 0);
                glColor3f (0.0f, 1.0f, 0.5f);glVertex3d(0, .8, 0);
                glColor3f (0.0f, 1.0f, 0.0f); glVertex3d(0, 0, 1);
                glEnd();
                glPopMatrix();
    Any help is appreciated.

  2. #2
    Crazy Fool Perspective's Avatar
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    sounds like you need to enable the depth buffer or something like that... it's been a while.

  3. #3
    Supermassive black hole cboard_member's Avatar
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    im drunk and i'm lisrenign to muse!!!!
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

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    Alright, I've tried adding in glEnable (GL_DEPTH_TEST) after the glClear, but doing that causes the polygon to not show up at all.

    I've also tried messing throwing in glDepthFunc, but I still can't manage to find a way to get it to work. What am I missing?

  5. #5
    Supermassive black hole cboard_member's Avatar
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    Sorry about that last post.
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

  6. #6
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    I was missing GL_DEPTH_BUFFER_BIT in my glClear() method.

    Problem solved. Thanks

  7. #7
    The Right Honourable psychopath's Avatar
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    Quote Originally Posted by ahluka
    Sorry about that last post.
    You're excused since Muse is awesome.

    /offtopic
    Memorial University of Newfoundland
    Computer Science

    Mac and OpenGL evangelist.

  8. #8
    Supermassive black hole cboard_member's Avatar
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    Quote Originally Posted by psychopath View Post
    You're excused since Muse is awesome.

    /offtopic
    H.A.A.R.P released today! WEWT!
    /offtopic
    Good class architecture is not like a Swiss Army Knife; it should be more like a well balanced throwing knife.

    - Mike McShaffry

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