Each node in GroIMP's graph has a set of properties. For example, every node has a name. A sphere additionally has a radius, a location in space, a shader which defines its appearance, and some other properties.
The basic geometric properties
of a geometric node can be set in its constructor: The class
Sphere declares the constructor
Sphere(float radius) which initializes the
radius with the specified value, for the turtle command
RU the constructor
RU(float radius) is defined which initializes the
rotation angle. However, there is no constructor in these classes
which initializes the name or (in case of the Sphere)
the shader. This is because generally it would not be feasible to provide
constructors for all combinations of properties which the modeller wants
to initialize.
Nevertheless, one often wants to initialize properties which are not
accessible through the constructor. For this purpose, the classes define
setter methods like
setRadius(float radius) in class
Sphere to initialize values of these properties.
These can be invoked immediately after the constructor with the help
of a special syntax (instance scope expressions
of the XL programming language) as in
Axiom ==> Sphere(1).(setShader(RED), setTransform(0, 0, 1));
As in this example, a constructor expression
(or in fact any expression) can be followed
by a "." and a parenthesized comma-separated list of method
invocations (or in fact statements). Within the parenthesized list,
the result of the constructor is used as the implicit this
for the method invocations. The example creates a sphere of radius 1,
sets its shader to the colour red and translates it to the relative location
(0, 0, 1). Such a coloured sphere is used in
this simple example, where you should have a look at the
method init. The methods swap
and grow will be discussed in the next sections.