OpenGL depth test not working as expected

I have a simple program to use depth test. It is not working as expected. The program draws X, Y axis and a sphere near the origin. If I don't turn on the GL_DEPTH_TEST, the sphere is drawn over the axis. If I turn on the GL_DEPTH_TEST, the axis are drawn over the sphere which I was not expecting. Can someone tell me what I did wrong ?

void  
glwid::initializeGL()  
{    
    glClearColor (0.0f, 0.0f, 0.0f, 1.0f);      
}  



void  
glwid::resizeGL(int width, int height)  
{  
    glViewport( 0, 0, (GLint)width, (GLint)height );  
    glMatrixMode( GL_PROJECTION );  
    glLoadIdentity();  

    gluPerspective ( 90, (GLint)width/ (GLint)height, 0.0, 200.0 );  
    glMatrixMode( GL_MODELVIEW );  
    glLoadIdentity()开发者_运维知识库;  
    glEnable (GL_DEPTH_TEST);  
}  


void  
glwid::paintGL()  
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  

    glMatrixMode (GL_MODELVIEW);  
    glLoadIdentity();  

    gluLookAt (0, 0, 100, 0, 0, 0, 0, 1, 0);  


    //  
    // X axis  
    //  
    glBegin( GL_LINES );  
    qglColor( green );  
    glVertex3f (-100.0,  0, 0. );  
    glVertex3f (100.0, 0, 0. );  
    glEnd();  


    //  
    // Y axis  
    //  
    glBegin( GL_LINES );  
    qglColor( red );  
    glVertex3f (0.0, 100.0, 0. );  
    glVertex3f (0.0, -100, 0. );   
    glEnd();  

    //  
    // sun  
    //  
    glTranslated (5, 0, 20);  
    GLUquadricObj *sphere_quadric = gluNewQuadric();  
    glColor3ub (255, 255, 0);  
    gluQuadricDrawStyle(sphere_quadric, (GLenum)GLU_SMOOTH);  
    gluSphere(sphere_quadric, 10, 36, 36);  
}  

I've tried your code. The problem is in resizeGL() function. The problem was your putting to

gluPerspective ( 90, (GLint)width/ (GLint)height, 0.0, 200.0 );  

0.0 value as a third argument. Put 0.01 for example - and everything will be ok. that's because this parameter should always be positive: http://www.opengl.org/sdk/docs/man/xhtml/gluPerspective.xml

Also change (GLint)width/ (GLint)height to (GLfloat)width/ (GLfloat)height otherwise the result will be strange.

And it's better to put glEnable(GL_DEPTH_TEST) into initializeGL() function

Your axis starts at Z location 0. The Sphere is at Z location 20 (farther away from the "camera") therefore the axis is in-front of the sphere and is being shown.

As you currently have it setup, as Z values go up they move away from the screen. As they go down, they are going closer to the screen.

You have two options: Disable depth testing while drawing your axis (therefore it will always be behind everything). Or move your axis to Z position 100 or so and scale it up to make it look the same size. Option one is probably better.

Simply wrapping your axis drawing routines in glDisable(GL_DEPTH_TEST); and glEnable (GL_DEPTH_TEST); should do the trick