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GLvoid display(GLvoid)

{

  glDrawBuffer(GL_BACK);                                   //draw into both back buffers

  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);      //clear color and depth buffers

  glDrawBuffer(GL_BACK_LEFT);                              //draw into back left buffer

  glMatrixMode(GL_MODELVIEW);

  glLoadIdentity();                                        //reset modelview matrix

  gluLookAt(-IOD/2,                                        //set camera position  x=-IOD/2

            0.0,                                           //                     y=0.0

            0.0,                                           //                     z=0.0

            0.0,                                           //set camera "look at" x=0.0

            0.0,                                           //                     y=0.0

            screenZ,                                       //                     z=screenplane

            0.0,                                           //set camera up vector x=0.0

            1.0,                                           //                     y=1.0

            0.0);                                          //                     z=0.0

  glPushMatrix();

  {

    glTranslatef(0.0, 0.0, depthZ);                        //translate to screenplane

    drawscene();

  }

  glPopMatrix();

  glDrawBuffer(GL_BACK_RIGHT);                             //draw into back right buffer

  glMatrixMode(GL_MODELVIEW);

  glLoadIdentity();                                        //reset modelview matrix

  gluLookAt(IOD/2, 0.0, 0.0, 0.0, 0.0, screenZ,            //as for left buffer with camera position at:

            0.0, 1.0, 0.0);                                //                     (IOD/2, 0.0, 0.0)

  glPushMatrix();

  {

    glTranslatef(0.0, 0.0, depthZ);                        //translate to screenplane

    drawscene();

  }

  glPopMatrix();

  glutSwapBuffers();

} 

The default framebuffer contains up to 4 color buffers, named GL_FRONT_LEFT, GL_BACK_LEFT, GL_FRONT_RIGHT, and GL_BACK_RIGHT. The left and right buffers are used for stereoscopic rendering. 

void display(void)

{

glClear(GL_COLOR_BUFFER_BIT);

glMatrixMode(GL_MODELVIEW); //GL_PROJECTION

glPushMatrix();

glViewport(0, 0, 250, 250); 

gluLookAt(0.10, 0.0, 0.2, 0.0, 0.0, -2.0, 0.0, 1.0, 0.0);

draw_sin();

glPopMatrix();

glPushMatrix();

glViewport(250, 0, 250, 250); 

gluLookAt(0.2, 0.0, 0.2, 0.0, 0.0, -2.0, 0.0, 1.0, 0.0);

draw_sin();

glPopMatrix();

glutSwapBuffers();

} 

8.010 How does the camera work in OpenGL?

As far as OpenGL is concerned, there is no camera. More specifically, the camera is always located at the eye space coordinate (0., 0., 0.). To give the appearance of moving the camera, your OpenGL application must move the scene with the inverse of the camera transformation.

8.020 How can I move my eye, or camera, in my scene?

OpenGL doesn't provide an interface to do this using a camera model. However, the GLU library provides the gluLookAt() function, which takes an eye position, a position to look at, and an up vector, all in object space coordinates. This function computes the inverse camera transform according to its parameters and multiplies it onto the current matrix stack.

[링크 : https://www.opengl.org/archives/resources/faq/technical/viewing.htm]

    [링크 : http://gamedev.stackexchange.com/.../why-do-we-move-the-world-instead-of-the-camera]