Elements are the basic computing and organizational entities available to the user. Elements are organized in a hierarchical structure similar to a UNIX directory tree. Each element embodies a specific computation in the simulation. This computation may implement part of the model being simulated or may be part of the graphical interface or file I/O.
The state of an element is contained in the element's fields. Fields may be of any C defined type. A field protection facility provides for both the visibility and accessability of the element fields. Fields have default values which define the state of an element's fields when the element is created. The default values may be changed, changing the initial values of elements created subsequently.
Elements may need information from other elements to perform their calculations. This information is gathered from the other elements' fields via Messages.
A set of default element types (called ``objects'') is distributed with GENESIS. They are used as templates for the creation of the particular elements which are used in a GENESIS simulation. One example of an element type is the `` neutral'' object which is often used to create an empty element used for grouping, much like a directory in the operating system. Another example is an ``xform'' object used to create graphical form widgets which might appear on the screen. The GENESIS distribution currently contains over eighty predefined objects. These are summarized in Objects.
The following GENESIS routines are used for creating and working with specific elements:
| Routine | Description |
| create | Creates new element of specified element type. |
| copy | Copies an element (and its children, if any) from one |
| portion of the element tree to another. | |
| createmap | Copies an element multiple times to form a |
| two-dimensional array. | |
| move | Moves an element and its children from one portion of the |
| tree to another. | |
| delete | Deletes an element and all of its children. |
| deleteall | Deletes all existing elements. [not recommended] |
| exists | Tests for existence of specified element or field. |
| reclaim | Reclaims memory from deleted elements. |
| addfield | Adds a new (extended) field to an element. |
| deletefield | Deletes an extended field of an element. |
| setfield | Sets value of field in data structure of specified element. |
| getfield | Returns value of field in data structure of specified element. |
| getfieldnames | Returns names of all existing fields in specified element. |
| showfield | Displays value of field in data structure of specified element. |
| save | Saves current field values for specified element in a file. |
| restore | Restores element state stored in file with save routine. |
| call | Allows an element to execute the function associated with |
| the named action. | |
| position | Sets xyz coordinates of an element and all of its children. |
| rotcoord | Rotates coordinates of elements in 3-d space. |
| egg | Generates coordinates for points on the surface of an ovoid. |
| plane | Generates 3-d coordinates for a plane with specified |
| dimensions and characteristics. | |
Other commands related to GENESIS elements are described in the sections on Hierarchical Structure, Objects, and Extended Objects.
Elements have defined actions which may be invoked explicity by the user via the call command. GENESIS calls many actions implicitly as a side effect of certain commands or as part of the process of running a simulation. The predefined actions of an element are inherited from the object which was used to create the element. Other actions may be added with the addaction command. The following predefined actions are common to many GENESIS objects.
| PROCESS | Called on each simulation step as described by the simulation |
| schedule to perform the element's update processing. | |
| INIT | Called on each simulation step as described by the simulation |
| schedule to initialize the element for this simulation step. | |
| RESET | Called when the simulation is reset (reset command) to allow |
| an element to reset itself to its default state. | |
| CHECK | Called from the check command to allow an element to verify |
| that it has all the information and the correct information | |
| needed to proceed with the simulation. | |
| SET | Called when an element field is set (or once for a setfield |
| command if SPECIAL_SET exists as an element field). The SET | |
| action must return 1 if it sets the field in question and 0 | |
| if it doesn't. | |
| SHOW | Called in order to perform special formating for field display |
| or retrieval (getfield or showfield commands). | |
| CREATE | Called when an element is created to initialize the element. |
| Must return non zero if the initialization is successful. | |
| COPY | Called when an element is copied. |
| DELETE | Called when an element is destroyed. |
| SAVE2 | Called to save the state of the element to a file. |
| RESTORE2 | Called to restore the previous state of the element from a file. |
| DUMP | Called by the simdump command. |
| UNDUMP | Called by the simundump command. |
Objects often have other predefined actions which are specific to the way the object is used. These are described in the documentation for the particular object. For a description of actions which are specific to XODUS elements (widgets), see XODUS Mouse Clicks.
If a particular action is not defined for an element, a default behavior is performed on the element (SET sets the field, SHOW returns the field, CREATE leaves fields initialized from defaults, etc.).