anim3D/src/CameraGO.i3

 Copyright (C) 1994, Digital Equipment Corporation                         
 Digital Internal Use Only                                                 
 All rights reserved.                                                      
                                                                           
 Last modified on Fri Sep 30 10:53:03 PDT 1994 by najork                   
       Created on Thu Feb 10 11:47:55 PST 1994 by najork                   


 A camera is a special kind of geometric object. Like any other geometric
   object, it can be a part of a group (and thus, by transitivity, of an
   entire scene), properties can be attached to it, and it observes both
   the properties attached to itself and to its ancestors in the scene.
   In particular, cameras are affected by transformation properties: When
   the transformation property of a camera or of one of its ancestors in
   the scene changes, the camera changes its position.


   Cameras are themselves invisible.


   CameraGO.T is the abstract class of all cameras. 


INTERFACE CameraGO;

IMPORT GO, Point3, PointProp, RealProp;

TYPE
  T <: GO.T;

 CameraGO.T is a subtype of \type{GO}{T}. No additional fiels or methods
   are defined. 

VAR
  From   : PointProp.Name;
  To     : PointProp.Name;
  Up     : PointProp.Name;
  Aspect : RealProp.Name;

 In addition to the properties observed by all \type{GO}{T}'s, there are four
   additional properties that are observed by all CameraGO.T's.


   From is the name of a property that describes the position of the
   camera. To is the name of a property that defines a point the camera
   is looking at. Up is the name of a property that defines the up-vector
   of the camera. From, To, and Up associate with property values of
   type \type{PointProp}{Val}.


   Aspect is the name of a property that defines the aspect ration
   (width / height) of the image generated by the camera. It associates with
   a \type{RealProp}{Val}. Its default value is 1, which means that the
   picture is not distorted
   (In the current implementation, the drawing area is always square). 
 The following four procedures make it more convenient to modify the
   From, To, Up, and Aspect properties of a camera: 


PROCEDURE SetFrom (o : GO.T; p: Point3.T);

 The expression SetFrom(o,p) is equivalent to
   o.setProp(From.bind(PointProp.NewConst(p))). 

PROCEDURE SetTo (o : GO.T; p: Point3.T);

 The expression SetTo(o,p) is equivalent to
   o.setProp(To.bind(PointProp.NewConst(p))). 

PROCEDURE SetUp (o : GO.T; p: Point3.T);

 The expression SetUp(o,p) is equivalent to
   o.setProp(Up.bind(PointProp.NewConst(p))). 

PROCEDURE SetAspect (o : GO.T; r: REAL);

 The expression SetAspect(o,r) is equivalent to
   o.setProp(Aspect.bind(RealProp.NewConst(r))). 

END CameraGO.