我想了解OpenGL的坐标系。我到处都看到它的描述为右撇子，但它不符合我的经验相一致。我试着画一些形状和三维物体和我看到的，显然z轴点到屏幕（能够在X点向右，而y起来 - 这是左手坐标系的描述）。我在想什么？

编辑： 例如： http://img576.imageshack.us/img576/9234/triangles.jpg 如果+ Z指向观众，为什么绿色三角形，其中，Z坐标是较大的，背后是红色的？

initializeGL：

  qglClearColor（QT ::深灰）;
glClearDepth（1.0）;
过glEnable（GL_DEPTH_TEST）;
glDepthFunc（GL_LEQUAL）;
过glEnable（GL_COLOR）;
 

resizeGL：

  glViewport（0，0，宽度，高度）;
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）;
在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（）;
在glBegin（GL_TRIANGLES）;
//红三角：
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）;
//绿三角：
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（）;
 

解决方案

最后2个参数的 glOrtho 参考：

nearVa​​l，farVal   指定距离的近远深度裁剪平面。 这些值是负的，如果飞机是被观察者的后面。

您更近剪裁平面是在观众面前远，落后。它会翻转Z轴。

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();

Last 2 parameters glOrtho reference:

nearVal, farVal Specify the distances to the nearer and farther depth clipping planes. These values are negative if the plane is to be behind the viewer.

Your nearer clipping plane is in front of the viewer and farther, behind. It'll flip Z axis.