OpenGL中，我画的点不在视景体内，为什么也能显示？？

Question

#include
void myDisplay()
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-2.0 * 64 / 48.0, 2.0 * 64 / 48.0, -2.0, 2.0, 0.1, 100);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(2.0, 2.0, 2.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_POINTS);
glVertex3f(0.0, 2.1, 0.0);
glEnd();
glFlush();
}void main(int argc, char ** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(640.0, 480.0);
glutInitWindowPosition(100, 100);
glutCreateWindow("point");
glutDisplayFunc(myDisplay);
glClearColor(1.0, 1.0, 1.0, 0.0);
glColor3f(0.0, 0.0, 0.0);
glPointSize(4.0);
glutMainLoop();

}
我画的那个点好像不在视景体内吧，怎么也能显示出来？？？