Creating the HRC - Microsoft Windows Pen API Programmer's Reference

Microsoft Windows Pen API Programmer's Reference

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Creating the HRC

Before recognition can occur, the application must create an HRC object. DoDefaultPenInput does this automatically for the system recognizer, or an application can call the CreateCompatibleHRC function to specify another recognizer. CreateCompatibleHRC takes two arguments: a handle to an existing HRC (if any) that serves as a template for the new HRC, and the handle to the recognizer that serves the new HRC.

Either or both arguments can be NULL. Giving NULL as the first argument creates a new HRC with default settings. The next section, "Configuring the HRC," describes the default parameters, which include the following settings:

Recognition ends after a brief period of inactivity or when the user taps outside the target window.
The target window does not use guides.
The recognizer returns only its best guess without alternative guesses.

Giving NULL as the second argument binds the HRC to the system default recognizer. Microsoft Windows sets the supplied file GRECO.DLL as the system default recognizer, specified in the Microsoft Windows 95 system registry. Refer to Appendix A for an explanation of how to change the default to another recognizer.

CreateCompatibleHRC, which is analogous to CreateCompatibleDC, copies configuration information from an existing HRC to the new HRC, which the application can then modify. The following fragment demonstrates how to load a fictitious recognizer called RECOG1.DLL and bind it to a new HRC patterned after an existing HRC called hrcTemplate:

HRC hrc1; // Handle to new HRC

HREC hrec1; // Module handle of recognizer

hrec1 = InstallRecognizer( "RECOG1.DLL" );

if (hrec1)

hrc1 = CreateCompatibleHRC( hrcTemplate, hrec1 );

Each HRC can access only one recognizer and the binding lasts the life of the HRC. To use multiple recognizers, an application must create multiple HRC objects, binding each to a different recognizer. The Pen API does not provide a means for changing the recognizer associated with an HRC.

As shown in the example above, an application must call InstallRecognizer to load any other recognizer it will use. The exception is the system default recognizer, which is already installed when the system starts up. An application should not install the system recognizer with InstallRecognizer. Doing so only creates an unnecessary module handle.

To preserve system resources, an application must free all handles obtained from InstallRecognizer with separate calls to UninstallRecognizer. Unlike other DLLs, a recognizer belongs to the system instead of the application. Windows does not unload the recognizer from memory until every client has called UninstallRecognizer.

Once it receives a valid HRC handle, the application can begin configuring the HRC to perform handwriting recognition.

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