The Spool Library: 2 Simple Printing Example

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Adding printing capability to an application is fairly simple, especially if it will be printing WYSIWYG. Somewhere in the application there is probably a message handler which is in charge of drawing the document. By including a Print Control object and writing handlers to some standard messages, it is a simple manner to redirect the document drawing commands to a printer.

Code Display 14-1 Printing Example

@include <spool.goh>
@object GenApplicationClass MyApp = {
	/* ...Much other GenApplication instance data omitted... */
	gcnList(MANUFACTURER_ID_GEOWORKS, GAGCNLT_SELF_LOAD_OPTIONS) = 
 		@MyPrintControl;
	ATTR_GEN_APPLICATION_PRINT_CONTROL = @MyPrintControl; 
}
@object PrintControlClass MyPrintControl = {
/* The PrintControlClass is a subclass of GenControlClass. Its "features"
 * correspond to the "Print" and "Fax" triggers in the File menu. Its instance
 * data contains information about the document to be printed, and links to
 * objects which will provide information. */
/* Single page documents would leave out page range UI from the Print dialog: 
	PCI_attrs = 		(@default & ~(PCA_PAGE_CONTROLS| PCA_VERIFY_PRINT)); 
	PCI_startUserPage = 1;
	PCI_endUserPage = 1 */
/* The PCI_output, or Print Output object, is in charge of supplying the graphics
 * commands describing the print job whenever the user wants to print. This object
 * is expected to handle a MSG_PRINT_CONTROL_START_PRINTING. */	
 * The print output object is normally either the model, target or process. */
	PCI_output = 		( TO_APP_TARGET ) ;
/* The PCI_docNameOutput object is supposed to provide the name of the document
 * on demand. This name is used to identify the document to the user in the Print
 * Control Panel. If this object is a GenDocumentGroup, it automatically does this.
 * If the object is not a GenDocumentGroup object, then * it must have a handler
 * for MSG_PRINT_GET_DOC_NAME that sends a nmae to the PrintControl via
 * MSG_PRINT_CONTROL_SET_DOC_NAME. */
	PCI_docNameOutput = MyGenDocumentGroup;
/* The PCI_docSize field specifies the size of the document to print (not to 
 * be confused with the size of the printer's paper). */
/* Many simple applications only support one document size,
 * and may specify it in the PrintControl and never bother with it again. 
 * We're setting the margins to all zero because they'll be updated via 
 * MSG_PRINT_CONTROL_GET_MARGINS. */
	PCI_docSizeInfo = {			(15/2*72), 
				(19/2*72), 
				0, 
				{0, 0, 0, 0}}; */
/* Many simple applications do not support multiple documents. These applications 
 * should set the GS_ENABLED flag of the PrintControl's GI_states field. */
}
@method MVTStartPrinting, MyVisTargetedClass, MSG_PRINT_START_PRINTING
/* We've set up our Print Control to send this message to the Target, so whatever
 * object will have the target when the user wants to print needs a handler for 
 * this message. We could have easily have put the Model or process in charge
 * of printing, changing PCI_output accordingly. It is often convenient to use
 * the same object to handle drawing to screen and to the printer. */
/* Arguments:		optr 		printControlOD,
		GStateHandle		gstate */
{
	PCMarginParams 	margins;
/*
 * 	Applications which allow the user to change the document size may handle
 *	the situation in more than one way. If the user has changed the page setup
 *	by working with a PageSizeControl, then the application has probably 
 * 	already been alerted to the page size. If the application has its own
 *	way of computing document size, it should use it. Such applications should
 * 	send MSG_PRINT_CONTROL_SET_DOC_SIZE and MSG_PRINT_CONTROL_SET_DOC_MARGINS 
 * 	to the PrintControl, either in this handler or else whenever the page size
 *	changes. Either time is fine, just so long as the document size is set
 * 	correctly by the time this MSG_PRINT_START_PRINTING handler is finished.
 *	Applications	 supporting only a single document size should probably set
 *	the size (and margins) in the PrintControl's instance data, as shown
 *	above. It is also possible to send a MSG_PRINT_CONTROL_SET_DOC_SIZE on
 *	every print, but if the size never changes, this is a bit wasteful.
 *	This application supports only one size of document. If the document
 *	doesn't fit on the page, the spooler will tile it onto multiple pages
 *	as necessary. It uses the printer's margins as the document margins: */
	@call 	MyPrintControl::MSG_PRINT_CONTROL_GET_PRINTER_MARGINS(
		&margins, 		/* Fill in structure with printer's margins */
		TRUE);		/* ...and automatically use printer margins
				 * as document margins */
	@call 	self::MSG_VIS_DRAW(DF_PRINT, gstate);
	/* If the MSG_VIS_DRAW handler didn't end with a form feed, put one in: 
	GrNewPage(gstate, PEC_FORM_FEED); */
	@send 	MyPrintControl::MSG_PRINT_CONTROL_PRINTING_COMPLETED();
}
@method MVTDraw, MyVisTargetClass, MSG_VIS_DRAW
/* Chances are, whatever object this is has some sort of draw handler already.
 * However, if you're building up this class from scratch, you'll be glad to
 * know that commands of the following form work just as well drawing in
 * response to a print request as they do drawing anything else: */
{	GrSetLineColor(gstate, CF_INDEX, C_RED, 0, 0);
	GrDrawLine(gstate, 144, 144, 288, 288);
	GrNewPage(gstate, PEC_FORM_FEED);
}
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