User`s guide

8 Using Events and Callbacks
8-2
Using Events and Callbacks
You can enhance the power and flexibility of your image acquisition application by
using event callbacks. An event is a specific occurrence that can happen while an image
acquisition object is running. The toolbox defines a set of events that include starting,
stopping, or acquiring frames of data.
When a particular event occurs, the toolbox can execute a function that you specify.
This is called a callback. Certain events can result in one or more callbacks. You can
use callbacks to perform processing tasks while your image acquisition object continues
running. For example, you can display a message, analyze data, or perform other tasks.
The start and stop callbacks, however, execute synchronously; the object does not
perform any further processing until the callback function finishes.
Callbacks are controlled through video input object properties. Each event type has an
associated property. You specify the function that you want executed as the value of the
property.
The following topics describe using events and callbacks.
• “Using the Default Callback Function” on page 8-3
• “Event Types” on page 8-5
• “Retrieving Event Information” on page 8-8
• “Creating and Executing Callback Functions” on page 8-12