A RootGO.T is a geometric object that describes a scene (that is, it is the root of a scene tree or DAG). RootGO.T is a subtype of \type{GroupGO}{T}.

INTERFACE RootGO;

IMPORT BooleanProp, CameraGO, ColorProp, GraphicsBase, GroupGO, Point, Point3,
       RealProp;

TYPE
  T <: Public;
  Public = GroupGO.T OBJECT
  METHODS
    init (cam : CameraGO.T; base : GraphicsBase.T) : T;
    changeCamera (cam : CameraGO.T);
    screenToWorld (pos: Point.T; z: REAL): Point3.T;
  END;

r.init(cam,base) initializes a new root object r and returns it. The scene (i.e.\ r and its descendants) will be viewed through the camera cam (which may, but does not have to be a descendant of r). base provides a connection to the underlying window system (e.g.\ X) and graphics system (e.g.\ PEX). It also initializes the animation clock to a new \type{Clock}{T} (i.e.\ a real-time clock).

r.changeCamera(cam) changes the camera through which the scene is viewed.

r.changeClock(clock) changes the animation clock.

r.animate(ah) starts the animation of all synchronized time-variant property values that are currently tied to the animation handle ah. r.animate(ah) returns when all animations associated with ah are completed.

PROCEDURE New (cam : CameraGO.T; base : GraphicsBase.T) : T;

A convenience procedure. The expression New(cam,base) is equivalent to NEW(T).init(cam,base).

PROCEDURE NewStd (base : GraphicsBase.T := NIL) : T
  RAISES {GraphicsBase.Failure};

Creates and returns a new RootGO.T, which is set up in a ``reasonable'' way. \begin{itemize} \item The new root (root) uses a perspective camera, which is looking at the origin. \item root contains two light sources, an ambient light source and a vector light source with rays along the vector (-1,-1,-1). Both sources are emitting white light. \item If no base is supplied, it creates a new X-PEX base entitled ``Anim3D Viewer''. \item The property (GO.Transform,TransformProp.NewConst ()) is attached to root. This property is used to allow the user to interactively manipulate the scene, and therefore should not be detached. \item Mouse and position callback objects are pushed onto root's mouse and position callback stacks. These callback objects respond to ``mouse drags'' (possibly modified through the shift key) by translating, uniformly scaling, or rotating the scene described by root. \end{itemize}

VAR
  Background         : ColorProp.Name;
  DepthcueSwitch     : BooleanProp.Name;
  DepthcueColour     : ColorProp.Name;
  DepthcueFrontPlane : RealProp.Name;
  DepthcueBackPlane  : RealProp.Name;
  DepthcueFrontScale : RealProp.Name;
  DepthcueBackScale  : RealProp.Name;

In addition to the properties observed by all \type{GO}{T}'s and \type{GroupGO}{T}'s, there are some additional properties that are observed by RootGO.T's:

Background is the name of a property that describes the background color of the scene. It associates with a \type{ColorProp}{Val}. By default, the background is black.

{\em Note: Alternatively, I could say that by default, the color shift shall occur in the direction of the background color.}

DepthcueSwitch is the name of a property that determines whether or not depth cueing (also called ``fog'') shall be used. It associates with a \type{BooleanProp}{Val}. By default, depth cueing is switched off.

DepthcueColour is the name of a property that determines the color of the ``fog'', i.e. the color shift objects that are far from the viewer undergo. It associates with a \type{ColourProp}{Val}. By default (assuming that depth cueing is activated) objects appear the darker the further they are away from the viewer (i.e.\ their color is shifted towards black).

DepthcueFrontPlane and DepthcueBackPlane are the names of two properties that determine within which distance range from the viewer the color shift shall occur. They associate with \type{RealProp}{Val}'s. Distances are specified in normalized projection coordinates.

{\em Note: This concept might be to complicated for a casual user. I could hide the depth cueing front and back planes, and set them to be equal to the z-buffer clamps. The user could still adjust the amout of depth cueing by adjusting the front and back scale.}

DepthcueFrontScale and DepthcueBackScale are the names of two properties that determine how strong the color shift shall be at the depth cueing front and back planes. They associate with \type{RealProp}{Val}'s.

END RootGO.