Some input ports cause the node to do something special when they receive an event. In the Count within Range node shown below, the Increment, Decrement, and Set Count ports each uniquely affect the count stored by the node — upon receiving an event, they increment the count, decrement the count, or change the count to a specific number. Likewise, in the Display Console Window node, the Write Line input port does something special when it receives an event — it writes a line of text to the console window. Each of these ports has a port action.
If an input port has a port action, then the node does something different when that input port receives an event than it does when any other input port receives an event. What counts as “something different”? Either the node outputs different data (immediately or later) or the node affects the world outside the composition differently.
Looking again at the Count within Range node, you can see that the node has some input ports with port actions and some without. For the ports without port actions — Minimum, Maximum, and Wrap Mode — the node will output the same number regardless of whether the event causing the node to execute has hit one of these ports. The node uses the data from these ports and doesn’t care if they received an event. For each of the ports with port actions, however, it makes a difference whether the event has hit the port. The Increment port, for example, only affects the count if the event came in through that input port.
Rather than affecting the node’s output data, as in the Count within Range node, the Display Console Window node’s port action affects the world outside the composition. When the Write Line input port receives an event, it doesn’t affect the data coming out of the node’s output ports. Rather, it affects what you see in the console window.
You can recognize an input port with a port action by the little triangle to the right of the port name. In Vuo, the triangle shape symbolizes events. The little triangle for the port action reminds you that this port does something unique when it receives an event.