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GEOS SDK TechDocs
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The Spool Library
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2 Simple Printing Example
By including a PrintControl object, an application gains access to the powers of the GEOS printing system. Below are several of the features built into GEOS:
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Single Imaging Model
You'll use the same commands to describe print jobs as you did for screen drawings. These commands work for all supported printers. Thus, anything you can draw can be printed, and the application doesn't have to worry about what model of printer is being used.
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Background Printing
Background printing allows users to continue working while their documents print. This is an example of multitasking at work. A process known as the Spooler spawns a separate thread for each active printer. Since each printer's thread priority is low, printing will take place in the background, interfering little with the user's interactions. If you want printing to take place in the foreground, your application can boost the priority of a printer thread.
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Standard UI Components
The PrintControl is a full-featured control object and it provides a UI mechanism for finding out what a user wants to print. For user choices which depend on the printer (for example, some printers have no low-quality mode), the PrintControl will take printer abilities into consideration.
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Control Over Scheduling
The Spooler normally handles jobs in FIFO (first in, first out) order. Geodes can exercise a great deal of control over the Spooler's scheduling of jobs. Any scheduling options the user might request using the Printer Control Panel, the application can request using spool routines.
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Managing the Printer Yourself
If you can't or won't use standard GEOS commands to describe a print job, you can use Raw Mode to send a packet of commands in the printer's own language. For example, you could send escape codes or commands from a page description language. Since this is a standard printing mode, you still benefit from all the usual spool scheduling features.
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Management of Multiple Printers
The user may have multiple printing devices hooked up and installed at one time. The system handles this situation intelligently: the Spooler maintains a separate queue for each serial or parallel port. Thus, if two printers are installed on two different ports, both may print at once. If two or more printers are installed on the same port then they share a queue. Thus, jobs for one printer won't try to print at the same time as those for another on the same port. To make sure the job prints to the correct printer, the Spooler will put up a dialog box advising the user to put the correct device on line.
| GEOS SDK TechDocs
|
| The Spool Library
| 2 Simple Printing Example