Glossary
application phase In QuickDraw GX printing, the phase when the application calls QuickDraw GX and interacts with the user by displaying dialog boxes to establish printing parameters, such as page orientation and paper type.background task A process that runs concurrently with another process without being the primary focus of the user's attention. The background task is allocated a percentage of the total processor time to accomplish its tasks. Several background tasks can be active at the same time. Compare foreground task.
default implementation The implementation of a printing message that is provided by QuickDraw GX. This is the code that executes if your printing extension or printer driver does not totally override the message.
despooling In QuickDraw GX printing, the process during the imaging phase of printing during which each previously spooled page is read from the spool file. See also imaging phase.
device communications phase In QuickDraw GX printing, the phase when the data that represents the rendered form of each page is sent to the output device. A printing extension or printer driver can only communicate with the printing device during this phase of printing.
foreground task The process that is currently the main task being executed by the system. This generally corresponds to the application that owns the frontmost window on the user's screen. There is only one foreground task at any given time.
forward To pass a message on to the next message handler in a message chain. See also message chain, message handler, override.
imaging phase In QuickDraw GX printing, the phase when each previously spooled page is rendered into a form that can be printed on the output device. The imaging phase is composed of two processes: despooling and rendering. See also despooling and rendering.
imaging system A part of the QuickDraw GX printing software that manages the conversion of QuickDraw GX shapes into data for a specific type of output device, including raster, vector, and PostScript printing devices. When the output device is a printing device, also referred to as a print imaging system. See also raster imaging system, vector imaging system, and PostScript imaging system.
message A notice sent by one message handler to another that a certain condition has arisen or that a certain task needs to be accomplished. See also printing message.
message chain A hierarchy of message handlers eligible to receive and respond to messages.
message handler A recipient of messages. In QuickDraw GX printing, applications, printing extensions, printer drivers, and QuickDraw GX are all message handlers, which are part of a message chain.
message override The response, by a message handler, of intercepting a message and taking some action. The response to a message is performed by an override function. See also override function.
message-passing architecture A software system driven by messages that are sent in response to certain conditions or events. The messages activate message handlers, which take action in response to the messages. QuickDraw GX printing uses a message-passing architecture.
override (n.) See message override and override function. (v.) To intercept a message and take action on it.
override function The code, defined in a message handler, that responds to a message. The formats of the functions that override specific printing messages are given in this book. See also message override.
partial override An implementation of a printing message override that forwards the message to other message handlers. You typically forward the message at the beginning or end of your override function.
PostScript imaging system The imaging system provided by QuickDraw GX that converts QuickDraw GX shapes into PostScript instructions and data for PostScript output devices such as the Apple LaserWriter family of printers.
printer driver A program that converts data that is sent by an application program into data and control sequences intended for a specific output device.
print imaging system See imaging system.
printing alert box An alert box used by QuickDraw GX printing to display information to the user that must be responded to. The alert box is like a dialog box in that it can contain control items. The user must explicitly dismiss an alert box to remove it from the screen.
printing extension An add-on software module that allows you to extend printing functionality provided by applications and printer drivers.
printing message A notice that QuickDraw GX sends to the message handlers in a message chain that a certain printing-related condition has arisen or that a certain printing-related task needs to be accomplished. See also message chain and message handler.
printing message override See message override.
raster imaging system The imaging system provided by QuickDraw GX that converts QuickDraw GX shapes into data and control sequences for raster output devices such as the Apple ImageWriter family of printers.
rendering In QuickDraw GX printing, the process during the imaging phase of printing during which each despooled page is converted into image data that can be printed by the output device. See also imaging phase.
spooling phase In QuickDraw GX printing, the phase when the application sends the document pages to disk, in preparation for printing. The printer driver stores printable output in a file from which it is subsequently despooled, rendered, and sent to the output device. See also despooling.
total override An implementation of a printing message override that does not forward the message to other message handlers.
vector imaging system The imaging system provided by QuickDraw GX that converts QuickDraw GX shapes into data and control sequences for vector output devices such as graphic plotters.
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