DTWAIN Application Loop Example

Implementing the TWAIN message loop in a DTWAIN application is a very simple process.  The DTWAIN version of the TWAIN message loop is simplified to the following construct: (Also see MFC Example)

#include <windows.h>

#include "dtwain.h"

...

MSG msg;

...

// Initialize DTWAIN

DTWAIN_SysInitialize( );

...

// Let DTWAIN know that the application will adjust the main loop

DTWAIN_SetTwainMode(DTWAIN_MODELESS);

...

while (GetMessage(&msg, NULL, 0, 0)) {

    if ( !DTWAIN_IsTwainMsg( &msg )) {

                 TranslateMessage(&msg);

                 DispatchMessage(&msg);

    }

 }

...

Except for the DTWAIN_SysInitialize call, the only change to the traditional message loop are the calls to DTWAIN_SetTwainMode and DTWAIN_IsTwainMsg. The DTWAIN_SetTwainMode with the DTWAIN_MODELESS value tells DTWAIN that the application will be responsible in letting TWAIN process the messages.  The DTWAIN_SetTwainMode should be called before the main application loop starts.

The DTWAIN_IsTwainMsg is the 'TWAIN Message processor'.  If DTWAIN_IsTwainMsg returns FALSE, the normal TranslateMessage and DispatchMessage Windows API functions called.  Otherwise, the message is not processed by the application.  The DTWAIN_IsTwainMsg is a very powerful function.  Not only does it determine whether the message is actually a TWAIN message, but also processes the message correctly.  Note that there is no switch or if-then statements that you would have to normally do if you were to process the TWAIN messages yourself without DTWAIN.