MATLAB IMAGE ACQUISITION TOOLBOX - RELEASE NOTES Guide de l'utilisateur télécharger pdf (Page 96)

5 Acquiring Image Data

5-18

Implementing the Acquisition Thread Function

This section describes how to implement your adaptor's acquisition thread function. In a

threaded adaptor design, the acquisition thread function performs the actual acquisition

of frames from the device. When you create the thread (“Opening and Closing Connection

with a Device” on page 5-10), you specify the name of this acquisition thread function as

the starting address for the new thread.

User Scenario

The toolbox engine invokes the acquisition thread function indirectly when a user calls

the start, getsnapshot, or preview function. Once called, the acquisition thread

function acquires frames until the specified number of frames has been acquired or the

user calls the stop function.

Suggested Algorithm

Note The design of the acquisition thread function can vary significantly between various

adaptors, depending on the requirements of the device's SDK. This section does not

describe device-dependent implementation details but rather highlights required tasks

that are common to all implementations.

At its highest level, in a threaded design, an acquisition thread function typically

contains two loops:

• “Thread Message Loop” on page 5-18

• “Frame Acquisition Loop” on page 5-20

Thread Message Loop

The thread message loop is the main processing loop in the acquisition thread function.

You create the thread in the openDevice() function. The acquisition thread function

enters the thread message loop, waiting for the message to start acquiring frames.

Your adaptor's startCapture() function sends the message to the acquisition thread,

telling it to start acquiring frames. This example uses the WM_USER message to indicate

this state. See “Sending a Message to the Acquisition Thread” on page 5-15 for more

information.

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MATLAB IMAGE ACQUISITION TOOLBOX - RELEASE NOTES Guide de l'utilisateur Page 96