Writing Callbacks

Callbacks provide a way for Quartz to inform your application of the status of the conversion. If your application has a user interface, you can use the status information to provide feedback to the user, as shown in Figure 15-1.

You can provide callbacks to inform your application that Quartz 2D is:

• Starting the conversion (CGPSConverterBeginDocumentCallback). Quartz 2D passes your callback a generic pointer to data you supply.

• Ending the conversion (CGPSConverterEndDocumentCallback). Quartz 2D passes your callback a generic pointer to data you supply and a Boolean value that indicates success (true) or failure (false).

• Starting a page (CGPSConverterBeginPageCallback). Quartz 2D passes your callback a generic pointer to data you supply, the page number, and a CFDictionary object, which is currently not used.

• Ending a page (CGPSConverterEndPageCallback). Quartz 2D passes your callback a generic pointer to data you supply and a Boolean value that indicates success (true) or failure (false)

• Progressing with the conversion (CGPSConverterProgressCallback). This callback is invoked periodically throughout the conversion. Quartz 2D passes your callback a generic pointer to data you supply.

• Sending a message about the process (CGPSConverterMessageCallback). There are several kinds of messages that can be sent during a conversion process. The most likely are font substitution messages, and any messages that the PostScript code itself generates. Any PostScript messages written to stdout are routed through this callback—typically these are debugging or status messages. In addition, there can be error messages if the document is malformed.

  Quartz 2D passes your callback a generic pointer to data you supply and a CFString object that contains a message about the conversion.

• Deallocating the PostScript converter object (CGPSConverterReleaseInfoCallback). You can use this callback to deallocate the generic pointer if you’ve provided data and to perform any additional postprocessing tasks. Quartz 2D passes your callback a generic pointer to data you supply.

See the CGPSConverter Reference for the prototype each callback follows.

Filling In a Callbacks Structure

You need to assign a version number and the callbacks you created to the appropriate fields of the CGPSConverterCallbacks data structure (shown in Listing 15-1). The version is 0. Assign NULL to those fields for which you do not supply a callback.

Listing 15-1  The PostScript converter callbacks data structure

struct CGPSConverterCallbacks {

   unsigned int version;

   CGPSConverterBeginDocumentCallback beginDocument;

   CGPSConverterEndDocumentCallback endDocument;

   CGPSConverterBeginPageCallback beginPage;

   CGPSConverterEndPageCallback endPage;

   CGPSConverterProgressCallback noteProgress;

   CGPSConverterMessageCallback noteMessage;

   CGPSConverterReleaseInfoCallback releaseInfo;

};

Creating a PostScript Converter Object

You call the function CGPSConverterCreate to create a PostScript converter object. This function takes three parameters:

• A pointer to generic data that you want passed to your callbacks. You can supply NULL if you don’t need to provide any data.

• A pointer to a filled-out CGPSConverterCallbacks data structure.

• NULL. This field is reserved for future use.

Creating Data Provider and Data Consumer Objects

You create a data provider object by calling the function CGDataProviderCreateWithURL, supplying a CFURL object that specifies the address of the PostScript file you want to convert.

Similarly, you create a data consumer object by calling the function CGDataConsumerCreateWithURL, supplying a CFURL object that specifies the address of the PDF document that results from the conversion.

Performing the Conversion

You call the function CGPSConverterConvert to perform the actual conversion from PostScript to PDF. This function takes as parameters:

• A PostScript converter object.

• A data provider object that supplies PostScript data.

• A data consumer object for the converted data.

• NULL. This parameter is reserved for future use.

The function returns true if the conversion is successful.

You can call the function CGPSConverterIsConverting to check whether the conversion is still progressing.