Where points OpenGL z-axis?

I'm trying to understand OpenGL coordinate system. Everywhere I see it's described as right-handed one, but it doesn't correspond with my experience. I tried to draw some shapes and 3-d objects and I see that apparently z-axis points "into the screen" (while x points to right, and y up - which is description of left-handed coordinate system). What am I missing?

edit: For example:
http://img576.imageshack.us/img576/9234/triangles.jpg
If +Z points viewer, why green triangle, which z-coordinate is larger, is behind red one?

initializeGL:

qglClearColor(Qt::darkGray);
glClearDepth(1.0);
glEnable(GL_DEPTH_TEST);
glDepthFunc( GL_LEQUAL );    
glEnable(GL_COLOR);

resizeGL:

glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-50.0f, 50.0f, -50.0f, 50.0f, 50.0, -50.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

paintGL:

glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glRotatef (-30.0, 1.0, 0.0, 0.0);
glRotatef (20.0, 0.0, 1.0, 0.0);
glColor3f(1.0, 0.0, 0.0);
glBegin(GL_LINES);
glVertex3f(45.0, 0.0, 0.0);
glVertex3f(-45.0, 0.0, 0.0);
glVertex3f(0.0, 45.0,  0.0);
glVertex3f(0.0, -45.0,  0.0);
glVertex3f( 0.0, 0.0, 45.0);
glVertex3f( 0.0, 0.0, -45.0);
glEnd();
glBegin(GL_TRIANGLES);
//Red triangle:
glColor3f(1.0, 0.0, 0.0);
glVertex3f(0.0, 0.0, 1.0);
glVertex3f(0.0, 20.0, 1.0);
glVertex3f(20.0, 0.0, 1.0);
//Green triangle:    
glColor3f(0.0, 1.0, 0.0);
glVertex3f(-15.0, 0.0, 20.0);
glVertex3f(0.0, 25.0, 20.0);
glVertex3f(15.0, 0.0, 20.0);
glEnd();

opengl 3d

Edit Report

Okay, the thing that stands out for me is the glOrtho function. You have the near and far clipping planes only 100 units apart. That seems very small. Do you really want it that way? It's represented by the last 2 parameters in that function.

Also your objects are very big in relation to this small frustum. Objects could be sitting directly in front of your camera and it would block other objects from being seen.

I would enlarge all the parameters in the glOrtho call. HTH

In a right-handed system (OpenGL) negative Z (-Z) should point into the screen. Positive Y should be "up," and positive X should be to the right.

This seems to be what you described, and that is a right-handed coordinate system.

Perhaps this can help. http://www.geometrictools.com/Documentation/LeftHandedToRightHanded.pdf

answered 2010-08-07T14:54:46.220

Where points OpenGL z-axis?

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