User`s guide

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 o ccurrence 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. Yo u specify the function that you want

executed as the value of the property.

Example: Using the Default

Callback F unction (p. 7-2)

Introduces events and callbacks by

showing a simple example

Event Types (p. 7-4)

Defines all the event types supported

by the toolbox

Retrieving Event Information (p. 7-7)

Describes the information generated

with each event and describes how

to access it

Creating and Executing Callback

Functions (p. 7-12)

Describes how to write a callback

function and associate it with an

event callback