1 ArtiSynth Overview

1.4 Properties

ArtiSynth components expose properties, which provide a uniform interface for accessing their internal parameters and state. Properties vary from component to component; those for RigidBody include position, orientation, mass, and density, while those for AxialSpring include restLength and material. Properties are particularly useful for automatically creating control panels and probes, as described in Section 5. They are also used for automating component serialization.

Properties are described only briefly in this section; more detailed descriptions are available in the Maspack Reference Manual and the overview paper.

The set of properties defined for a component is fixed for that component’s class; while property values may vary between component instances, their definitions are class-specific. Properties are exported by a class through code contained in the class definition, as described in Section 5.2.

1.4.1 Querying and setting property values

Each property has a unique name that can be used to access its value interactively in the GUI. This can be done either by using a custom control panel (Section 5.1) or by selecting the component and choosing Edit properties ... from the right-click context menu).

Properties can also be accessed in code using their set/get accessor methods. Unless otherwise specified, the names for these are formed by simply prepending set or get to the property’s name. More specifically, a property with the name foo and a value type of Bar will usually have accessor signatures of

  Bar getFoo()
  void setFoo (Bar value)

1.4.2 Property handles and paths

A property’s name can also be used to obtain a property handle through which its value may be queried or set generically. Property handles are implemented by the class Property and are returned by the component’s getProperty() method. getProperty() takes a property’s name and returns the corresponding handle. For example, components of type Muscle have a property excitation, for which a handle may be obtained using a code fragment such as

  Muscle muscle;
  Property prop = muscle.getProperty ("excitation");

Property handles can also be obtained for sub-components, using a property path that consists of a path to the sub-component followed by a colon ‘:’ and the property name. For example, to obtain the excitation property for a sub-component located by axialSprings/lad relative to a MechModel, one could use a call of the form

  MechModel mech;
  Property prop = mech.getProperty ("axialSprings/lad:excitation");

1.4.3 Composite and inheritable properties

Figure 1.1: Inheritance of a property named stiffness among a component hierarchy. Explicit settings are in bold; inherited settings are in gray italic.

Composite properties are possible, in which a property value is a composite object that in turn has sub-properties. A good example of this is the RenderProps class, which is associated with the property renderProps for renderable objects and which itself can have a number of sub-properties such as visible, faceStyle, faceColor, lineStyle, lineColor, etc.

Properties can be declared to be inheritable, so that their values can be inherited from the same properties hosted by ancestor components further up the component hierarchy. Inheritable properties require a more elaborate declaration and are associated with a mode which may be either Explicit or Inherited. If a property’s mode is inherited, then its value is obtained from the closest ancestor exposing the same property whose mode is explicit. In Figure (1.1), the property stiffness is explicitly set in components A, C, and E, and inherited in B and D (which inherit from A) and F (which inherits from C).