void display(void) {    glClear(GL_COLOR_BUFFER_BIT);    glColor3f(1.0, 1.0, 1.0);    glBegin(GL_LINES);    glVertex3d(0.75, 0.25, 0.0);    glVertex3d(0.75, 0.25, -0.75);    glEnd();    glFlush();}void init(void) {    glClearColor(0.0, 0.0, 0.0, 0.0);    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);}I should be able to see line from (0.75, 0.25, 0.0)  to (0.75, 0.25, -0.75), but I can't see anything on the screen.However, I'm able to see the line using snippet belowglVertex3d(0.35, 0.25, 0.0);glVertex3d(0.75, 0.25, -0.75);Can anyone explain this behavior?
glOrtho() in fixed function pipeline - Unable to see change in z-axis
opengl