A `DiskGO.T`

is a geometric object describing a disk.

INTERFACEDiskGO ; IMPORT GO, Point3, PointProp, RealProp, SurfaceGO; TYPE T <: Public; Public = SurfaceGO.T OBJECT METHODS init (prec := 10) : T; END;

`disk.init(prec)`

initializes a new disk`disk`

, whose surface is approximated by a polygon with`prec`

edges, and returns it. The location, orientation, and radius of the disk is determined by the three properties`Center`

,`Normal`

, and`Radius`

.

VAR Center : PointProp.Name; Normal : PointProp.Name; Radius : RealProp.Name;

In addition to the properties observed by all \type{GO}{T}'s and \type{SurfaceGO}{T}'s, there are three additional properties that are observed by`DiskGO.T`

's:

`Center`

is the name of a property that describes the center of the disk. It associates with a \type{PointProp}{Val}. If no`Center`

property is specified, the disk is centered around the origin.

`Normal`

is the name of a property that describes the normal vector of the disk. It associates with a \type{PointProp}{Val}. If no`Normal`

property is specified, the normal vector is taken to be (0,0,1).

`Radius`

is the name of a property that describes the radius of the disk. It associates with a \type{RealProp}{Val}. If no`Radius`

property is specified, the disk has a radius of 1.

Assume that in a given context and at a given point in time, the property mapping is such that`Center`

maps to a point property value which evaluates to`p`

,`Normal`

maps to a point property value which evaluates to`n`

, and`Radius`

maps to a real property value which evaluates to`r`

.`p`

,`n`

, and`r`

define the position and shape of the disk in this context and at this time as shown below: \begin{center} \begin{tabular}{c} \psfig{figure=images/DiskGO.ps,silent=} \end{tabular} \end{center}

PROCEDURE New (p : Point3.T; n : Point3.T; r : REAL; prec := 10) : T;

The following three procedures provide sugaring to attach`New(p,n,r,prec)`

creates a new disk, whose surface is approximated by a polygon with`prec`

edges, and returns it. It also attaches the following properties to the new cone: \begin{verbatim} (Center,PointProp.NewConst(p)) (Normal,PointProp.NewConst(n)) (Radius,RealProp.NewConst(r)) \end{verbatim}

`Center`

, `Normal`

, and `Radius`

properties with non-animated
property values to geometric objects:
PROCEDURE SetCenter (o : GO.T; p : Point3.T);

The expression`SetCenter(o,p)`

is equivalent to`o.setProp(Center.bind(PointProp.NewConst(p)))`

.

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

The expression`SetNormal(o,p)`

is equivalent to`o.setProp(Normal.bind(PointProp.NewConst(p))))`

.

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

The expression`SetRadius(o,r)`

is equivalent to`o.setProp(Radius.bind(RealProp.NewConst(r))`

.

END DiskGO.