NAME         place_cam - show icon of camera and view for interactive placement

AUTHOR       anonymous, AVS Inc.

TYPE         Geometry camera control module

DESCRIPTION

  This module is a prototype of a camera placement system. 
  Two geometry viewers are used, where the first has the object
  list plus an iconic representation of the camera, with
  view frustrum shown in wire frame.
  The second view is the scene that camera "sees" as placed
  in the first scene.
  The module shows how to manipulate and control camera
  and scene transformation matrices.

Notes:

 This module can be used to demonstrate how the "camera parameters" operate.
 It has several problems that prevent it from being a "general purpose"
 module.  It probably works best as a tutorial or example.

 There are two modes in which it "sort of" works.  The first mode, you
 have two geometry viewer scenes, one connected to the left output port
 the the other connected to the right.  Make sure to read or pipe the
 objects you want to view into both geometry viewer modules.
 One geometry viewer module will display an icon representing the camera.
 You can rotate the camera in the scene or the top level object to get
 an idea of how the "camera" relates to the objects.
 The other geometry scene contains the "camera view" described by the
 first scene.   If you select and rotate the camera icon in the first view,
 it will update the camera position and orientation in the second view.
 You can also change the front/back and other clip planes by adjusting the
 parameters.

 Here are the limitations of this mode:
   * you cannot rotate the object in either scene as they are not
     tied together.
   * you cannot rotate the top or any object in the other scene.

 The second mode is very much like the first mode except that you only
 have one geometry viewer module.  Connect both output ports to the
 inputs of this module.  Go into the geometry viewer menu and create a
 new camera with the "Create Camera" button.  The original camera that you
 display will be the icon view, the new camera will display the resulting
 camera defined by this view.

 Here are the limitations of this mode:
   * the refreshes are not synchronized properly when you rotate the
     camera icon.
   * you cannot rotate the top level object in either view.  In order to
     move the objects in the camera view, you have to transform the camera.
     (using the Transform Camera button).