Inside Macintosh: QuickDraw GX Printing Extensions and Drivers /

Chapter 2 - Printing Extensions / Using Resources in Printing Extensions

Defining the Loading Order of Your Extension

You also need to include an extension load ('load') resource for your printing extension to tell QuickDraw GX the default value that specifies where to load your extension into the printing message chain. If you have one or more message overrides that prefer to handle a message before or after other handlers, you can specify that in
this resource. The value that you define in your extension load resource specifies the default loading order for your extension when it is first added to the system. The user can modify the loading order of extensions by using the Extension Setup dialog box.

Note

The value that you specify in the extension load resource for your extension provides a default. It is used by QuickDraw GX as a hint. Because the user can change the order, you do not have any guarantee regarding the load order of your extension.

The constants for the values that you can specify in your extension load resource are shown in Table 2-7.

Table 2-7 Loading order constants for an extension

Constant	Explanation
gxExtensionLoadFirst	This extension is loaded as the top message handler in the printing message chain
gxExtensionLoadAnywhere	This extension can be loaded anywhere in the print message chain because its message overrides don't depend on a handling order
gxExtensionLoadLast	This extension is loaded as the bottom message handler in the print message chain

The extension load resource for the background picture printing extension is shown in Listing 2-25.

Listing 2-25 The extension load resource for the background picture extension

resource gxExtensionLoadType (gxExtensionLoadID,sysHeap,purgeable)
{
   gxExtensionLoadFirst
};

The background picture extension draws the background picture on each page after the page has been fully composed. Thus, this printing extension should be loaded first in the message chain, which means that it receives messages after all other message handlers. Then the printer driver and any other message handler can modify the page contents at despool time prior to the background picture being drawn.

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