Event-based management
- Last UpdatedApr 24, 2024
- 2 minute read
Events
The AVEVA™ XR engine scripting language is not an imperative and procedural language, but a relational one. At the root of this kind of language, there are the objects or nodes. Each node is characterized by a list of properties. When the properties of a node change, we speak about events.
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When the properties of a node change, this generates an event. You can link the property of a (source) node to the property of another (target) node so that when the first changes and generates an event, the change propagates to the second node. This is called an event propagation chain. |
Types of statements in a script
Scripts consist mostly of two kinds of statements.
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Statement type |
Description |
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Object definitions |
Declare logic or 3D scene related objects. |
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Connection definitions |
Declares how a node field change is routed to another node field. |
Non-routable fields
There are parameters that work only as input parameters (command parameters) and also parameters that cannot be overwritten because they are automatically filled by the engine at every frame (read-only parameters).
Note: Although all the parameters of a node may be considered event parameters, it is not always possible to use them all to route to another node parameters.
Event propagation is one-directional
The link between two parameters of the same or different nodes is one-directional. If the source field changes, then this change propagates to the target parameters. But if the target parameters changes, then nothing happens to the source parameters. You cannot set up bi-directional links other than to explicitly create two separate links. This kind of bi-directional link is likely to cause problems.
Different source parameters can connect the same target parameters. The value of the target parameters changes according to the order of the events coming from all its source parameters. The source parameters have no connection to each other besides their relationship to the target parameters.