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 DPS 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.
Inherits From: NSObject
Conforms To: NSObject (NSObject)
Declared In: DPSClient/NSDPSContext.h
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 Client Library Functions. 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 Types and Constants. 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
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.
- (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.
+ (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.