Depth Buffer in OpenGL

Question

I am trying to draw a series of rectangles using OpenGL but some of the ones that should appear below a rectangle appear above it.

To enable the depth function I am using

glClearDepth(1.0f);
glDepthFunc(GL_LESS);
glEnable(GL_DEPTH_TEST);

I am using gluLookAt at the begining of each draw. Here is an image of the problem. The blue rectangles are positioned with higher y values than the green rectangles.

alt text

As you can see in the top image some of the green rectangles appear above the blue ones. Any idea why this is happening and what I can do to fix it? Could it have something to do with the order that I'm drawing the rectangles?

Gordon Childs · Accepted Answer · 2009-06-25 21:20:14Z

12

When you clear your colour buffer are you also clearing the depth buffer?

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

Are you sure the image isn't correct? Some of those green squares actually
do look higher than the blue ones.

edited Jun 25, 2009 at 21:20

answered Jun 25, 2009 at 20:52

Gordon Childs

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Christopher · Accepted Answer · 2009-06-25 20:30:36Z

7

Did you enable the depth buffer in whatever windowing system you are using? For example, using glut you might need to: glutInitDisplayMode(GLUT_DEPTH | ....);

answered Jun 25, 2009 at 20:30

Christopher

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2 Comments

DHamrick Over a year ago

I am using qt for my windowing toolkit. I am not aware of any function like that. Do you know if there is one I should be calling simmilar to glut's function.

ravuya Over a year ago

In the QGLFormat object, you should be able to check if the depth buffer is enabled with the depth and setDepth methods.

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