Copyright ã1994 by NeXT Computer, Inc.  All Rights Reserved.

3

Display PostScript

Classes

Classes listed here and the protocol in the following section constitute OpenStep's object-oriented interface to the Display PostScript System. As such, many of the argument and return types that appear below (specifically, those having a ªDPSº prefix) are not described in this document. Rather, they are detailed in the specification for the Display PostScript System itself, as found in the Display PostScript System, Client Library Reference Manual, by Adobe Systems Incorporated. 

NSDPSContext

Inherits From:	NSObject 

Conforms To:	NSObject (NSObject)

Declared In:	DPSClient/NSDPSContext.h 

Class Description

The NSDPSContext class is the programmatic interface to objects that represent Display PostScript System contexts. A context can be thought of as a destination to which PostScript code is sent for execution. Each Display PostScript context contains its own complete PostScript environment including its own local VM (PostScript Virtual Memory). Every context has its own set of stacks, including an operand stack, graphics state stack, dictionary stack, and execution stack. Every context also contains a FontDirectory which is local to that context, plus a SharedFontDirectory that is shared across all contexts. There are three built-in dictionaries in the dictionary stack. From top to bottom, they are userdict, globaldict, and systemdict. userdict is private to the context, while globaldict and systemdict are shared by all contexts. globaldict is a modifiable dictionary containing information common to all contexts. systemdict is a read-only dictionary containing all the PostScript operators.

At any time there is the notion of the current context. The current context for the current thread may be set using setCurrentContext:.

NSDPSContext objects by default write their output to a specified data destination. This is used for printing, FAXing, and for generation of saved EPS (Encapsulated PostScript) code. The means to create contexts that interact with displays are platform-specific. 

The NSApplication object creates a context by default.

NSDPSContext Objects and Display PostScript System Context Records

When an NSDPSContext object is created, it creates and manages a DPSContext record. Programmers familiar with the client side C function interface to the Display PostScript System can access the DPSContext record by sending a context message to an NSDPSContext object. You can then operate on this context record using any of the functions or single operator functions defined in the Display PostScript System client library. Conversely, you can create an NSDPSContext object from a DPSContext record with the DPSContextObject() function, as defined in ªClient Library Functionsº. You can then work with the created NSDPSContext object using any of the methods described here.

General Exception Conditions

A variety of exceptions can be raised from NSDPSContext. In most cases, exceptions are raised because of errors returned from the Display PostScript Server. Exceptions are listed under ªTypes and Constants.º Also see the Display PostScript System, Client Library Reference Manual, by Adobe Systems Incorporated, for more details on Display PostScript System error names and their possible causes.

Initializing a Context

- initWithMutableData:(NSMutableData *)data	Initializes a newly allocated NSDPSContext that writes its
forDebugging:(BOOL)debug		output to data using the language and name encodings
languageEncoding:(DPSProgramEncoding)langEnc	 
nameEcoding:(DPSNameEncoding)nameEnc	 	specified by langEnc and nameEnc. The callback
textProc:(DPSTextProc)tProc		functions tProc and errorProc handle text and errors
errorProc:(DPSErrorProc)errorProc		generated by the context. If debug is YES, the output is given in human-readable form in which large structures
(such as images) may be represented by comments. 

Testing the Drawing Destination

- (BOOL)isDrawingToScreen	Returns YES if the drawing destination is the screen.

Accessing Context Data

- (NSMutableData *)mutableData	Returns the receiver's data object.

Setting and Identifying the Current Context

+ (NSDPSContext *)currentContext	Returns the current context of the current thread.

+ (void)setCurrentContext:(NSDPSContext *)context
	Installs context as the current context of the current thread.

- (DPSContext)DPSContext	Returns the corresponding DPScontext.

Controlling the Context

- (void)flush	Forces any buffered data to be sent to its destination.

- (void)interruptExecution	Interrupts execution in the receiver's context.

- (void)notifyObjectWhenFinishedExecuting:(id <NSDPSContextNotification>)object
	Registers object to receive a contextFinishedExecuting: message when the NSDPSContext's destination is ready to receive more input.

- (void)resetCommunication	Discards any data that hasn't already been sent to its destination.

- (void)wait	Waits until the NSDPSContext's destination is ready to receive more input.

Managing Returned Text and Errors

+ (NSString *)stringForDPSError:(const DPSBinObjSeqRec *)error	
	Returns a string representation of error.

- (DPSErrorProc)errorProc	Returns the context's error callback function.

- (void)setErrorProc:(DPSErrorProc)proc	Sets the context's error callback function to proc.

- (void)setTextProc:(DPSTextProc)proc	Sets the context's text callback function to proc.

- (DPSTextProc)textProc	Returns the context's text callback function.

Sending Raw Data

- (void)printFormat:(NSString *)format,...	Constructs a string from format and following string objects (in the manner of printf()) and sends it to the context's destination.

- (void)printFormat:(NSString *)format	Constructs a string from format and argList (in the
arguments:(va_list)argList	 	manner of vprintf()) and sends it to the context's destination.

- (void)writeData:(NSData *)buf	Sends the PostScript data in buf to the context's destination.

- (void)writePostScriptWithLanguageEncodingConversion:(NSData *)buf
	Writes the PostScript data in buf to the context's destination. The data, formatted as plain text, encoded tokens, or a binary object sequence, is converted as necessary depending on the language encoding of the receiving context.

Managing Binary Object Sequences

- (void)awaitReturnValues	Waits for all return values from the result table.

- (void)writeBOSArray:(const void *)data	Write an array to the context's destination as part of a
count:(unsigned int)items		a binary object sequence. The array is taken from data 
ofType:(DPSDefinedType)type		and consists of items items of type type.

- (void)writeBOSNumString:(const void *)data	Write a number string to the context's destination as part of 
length:(unsigned int)count		a binary object sequence. The string is taken from data
ofType:(DPSDefinedType)type		as described by count, type, and scale.
scale:(int)scale

- (void)writeBOSString:(const void *)data	Write a string to the context's destination as part of a
length:(unsigned int)bytes		binary object sequence. The string is taken from bytes (a count) of data.

- (void)writeBinaryObjectSequence:(const void *)data	
length:(unsigned int)bytes	Write a binary object sequence to the context's destination. The sequence consists of bytes (a count) of data.

- (void)updateNameMap	Updates the context's name map from the client library's name map.

Managing Chained Contexts

- (void)chainChildContext:(NSDPSContext *)child	Links child (and all of it's children) to the receiver as its chained context, a context that receives a copy of all PostScript code sent to the receiver. 

- (NSDPSContext *)childContext	Returns the receiver's child context, or nil if none exists.

- (NSDPSContext *)parentContext	Returns the receiver's parent context, or nil if none exists.

- (void)unchainContext	Unlinks the child context (and all of it's children) from the receiver's list of chained contexts.

Debugging Aids

+ (BOOL)areAllContextsOutputTraced	Returns YES if the data flowing between the application's contexts and their destinations is copied to diagnostic output.

+ (BOOL)areAllContextsSynchronized	Returns YES if all NSPDSContext objects invoke the wait method after sending each batch of output.

+ (void)setAllContextsOutputTraced:(BOOL)flag	Causes the data (PostScript code, return values, etc.) flowing between the all the application's contexts and their destinations to be copied to diagnostic output.

+ (void)setAllContextsSynchronized:(BOOL)flag	Causes the wait method to be invoked each time an NSDPSContext object sends a batch of output to its destination.

- (BOOL)isOutputTraced	Returns YES if the data flowing between the application's single context and its destination is copied to diagnostic output.

- (BOOL)isSynchronized	Returns whether the wait method is invoked each time the receiver sends a batch of output to the server.

- (void)setOutputTraced:(BOOL)flag	Causes the data (PostScript code, return values, etc.) flowing between the application's single context and the Display PostScript server to be copied to diagnostic output.

- (void)setSynchronized:(BOOL)flag	Sets whether the wait method is invoked each time the receiver sends a batch of output to its destination.