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                               About Printing
 
This topic describes how to print graphics and text to printers and
plotters. You should also be familiar with the following topics:
 
    ◄Presentation spaces and device contexts►
    ◄Graphics programming interface►
    ◄Profile manager►
    ◄Drawing in windows►
 
About Printing
 
The way an MS OS/2 application prints text and graphics is similar to the
way it displays text and graphics on the screen. In both cases, the
application uses the same Gpi functions and can isolate the task of creating
graphics from the task of sending them to an output device. For example, a
word processor can display text in a window by calling Gpi character and
string-drawing functions. When the user wants to print the text, the
application can use the same Gpi functions; the only difference is that the
output device is a printer instead of the screen. Printing can be thought of
as drawing in a window the size of a sheet of paper.
 
The Print Queue and the Spooler
 
An application may share a printer with other applications in the system or
with applications running on other systems in a network. When an application
sends output to a printer, it should be able to continue with other
processing while the print job is being completed. When several applications
request print jobs at the same time, the system should handle the print jobs
without forcing any of the applications to resend the jobs or wait for the
jobs to be completed. These tasks are handled in MS OS/2 by Print Manager,
the spooler, and the queue processor.
 
Printer Installer (pmprinst.exe) is a Presentation Manager utility that
installs a printer device driver and associates the driver with a queue.
Printer Installer provides a simpler user interface than did the previous
method of setting up the printing environment, which required the user to
work with Control Panel and Print Manager.
 
Print Manager (pmspool.exe) is a Presentation Manager utility that allows
the user to view print queues, printer configurations, and queued print
jobs. The user can also use Print Manager to cancel print jobs, change
printer and queue configurations, and change the default printer and queue
for Presentation Manager applications. (The user typically sets the default
printer and queue by using Printer Installer, however.) Print Manager works
with the spooler (pmspl.dll) to coordinate print jobs as they wait to be
processed by the queue processor (pmprint.qpr). In MS OS/2 version 1.21, the
spooler and Print Manager are always active.
 
Most print jobs are in the form of metafiles when the spooler receives them.
The queue processor (also called the queue driver or print processor)
translates the contents of the metafile into printer-specific commands and
sends these commands to the printer. (In other words, the queue processor
"plays" the metafile on the device context of a printer driver.) For more
information about metafiles, see the ◄Metafiles► topic.
 
The queue and printer names and their associated device drivers are stored
in the os2sys.ini file (os2.ini for MS OS/2 version 1.1). The user defaults
are stored in the os2.ini file.
 
Although most users will use Printer Installer (pmprinst.exe) to
simultaneously set up a printer and an associated queue, a user could still
use Control Panel and Print Manager to set up a printer without setting up a
queue. Such a printer is called a direct printer, because print jobs are
sent directly from the printer device driver to the physical port without
going through the spooler or queue processor. Some printer device drivers
(for example, pscript.drv) work with ASCII text instead of binary
information; these drivers can use direct printing to send output directly
to a file. Only one application at a time can print to a direct printer. The
application does not need to determine whether its print jobs are going to
the spooler or to a direct printer; the only difference if the user has set
up a direct printer is that, before continuing with other processing, an
application may have to wait for printing to finish.
 
Printer Selection
 
Before an application prints a document, it should determine what printers
are available on the system and display their names to the user, so that the
user can select which printer to use. If the application has previously
stored the preferred printer device driver for a document as one of the
document's "job properties," the printer that matches the specified driver
and model should be given as the default choice. Otherwise, the application
should give the system default printer as the default selection. The first
task in printing is to determine whether any of the printers on the system
match the job properties that may have been stored with the document.
 
Job Properties
 
Job properties describe characteristics of a print job that can be modified
on a document-by-document basis──for example, paper orientation (portrait or
landscape), print quantity, and paper form. After an application retrieves
job properties, either from the device driver or from extended attributes
stored with the document to be printed, it should allow the user to modify
those job properties before beginning the print job. If the user chooses job
properties that are different from the system default, the application
should store the new job properties with the document as extended
attributes. For information on storing and retrieving extended attributes,
see the ◄Extended Attributes► topic.
 
Data Retrieval from Initialization Files
 
The initialization files, os2sys.ini and os2.ini, contain information in
binary form about the configuration of the system, including information
about the printers that the system supports. An application can use the
PrfQueryProfileString function to retrieve information from these files.
(PrfQueryProfileString works only in MS OS/2 versions 1.2 and later. If an
application requires compatibility with earlier versions of MS OS/2, it
should use the WinQueryProfileString function.) If job properties were
stored with a document, an application can call PrfQueryProfileString until
it finds a match between the job properties and the available printers. If
the application cannot obtain an exact match between the job properties and
the capabilities of available printers, it should use the default queue and
printer that the user has defined. The system stores the system default
queue and printer device driver in the os2.ini file; the default settings
for each queue and printer supported by the system are in the os2sys.ini
file.
 
An application can use PrfQueryProfileString to retrieve many different
kinds of information from the os2.ini and os2sys.ini files, by specifying
which file to query in the first parameter and specifying an application
name and a keyname in the second and third parameters, respectively. (An
application can also use the DevQueryDeviceNames function to retrieve
information about a particular printer device driver, although it will still
need to use PrfQueryProfileString to retrieve the name of the device
driver.)
 
To retrieve the system default printer device driver or queue from os2.ini,
the application specifies HINI_USERPROFILE as the first parameter of
PrfQueryProfileString, PM_SPOOLER for the application name, and either
PRINTER or QUEUE for the keyname.
 
To retrieve data from os2sys.ini, the application specifies
HINI_SYSTEMPROFILE as the first parameter of PrfQueryProfileString. If the
application needs information about the printer, it supplies the printer
name as the keyname. The following list shows the application names that an
application can use when querying printer data from the os2sys.ini file and
the format of the data the function returns:
 
Application name          Format
────────────────────────────────────────────────────────────────────────────
PM_SPOOLER_PRINTER        port;driver(s);queue(s);printer parms;
 
PM_SPOOLER_PRINTER_DESCR  queue descr;
 
If the application requires information about the queue, it supplies the
queue name as the keyname. The following list shows the application names
that an application can use when querying queue data from the os2sys.ini
file and the format of the data the function returns:
 
Application name         Format
────────────────────────────────────────────────────────────────────────────
PM_SPOOLER_QUEUE         processor;queue parms;queue net parms;
 
PM_SPOOLER_QUEUE_DESCR   queue descr;
 
PM_SPOOLER_QUEUE_DD      driver;
 
PM_SPOOLER_QUEUE_DDDATA  driver data
 
Notice that the driver data returned when an application specifies
PM_SPOOLER_QUEUE_DDDATA is not followed by a semicolon. If an application
uses this application name in a call to the PrfQueryProfileString function,
it must parse the driver data carefully.
 
If an application specifies PM_SPOOLER_PRINTER as the application name, the
string returned by PrfQueryProfileString may contain more information than
the application needs. If there is more than one printer device driver or
queue associated with a port, all of the driver and queue names are returned
in the string. (When there is more than one driver or queue, the default
driver or queue is listed first.) Similarly, if model information is
associated with a printer device driver, the driver name is followed by a
period and the model information follows the period. The string returned by
a call to PrfQueryProfileString that specified PM_SPOOLER_PRINTER could look
like the following:
 
LPT1;EPSON.24-PIN 80 COL,PSCRIPT;LPT1Q,QUEUE2;;
 
In this case, port LPT1 is associated with two printer drivers and two
queues. EPSON is the default driver and LPT1Q is the default queue. The
epson driver is followed by information about the printer model.
 
When an application specifies PM_SPOOLER_QUEUE_DD, model information, if
any, follows the driver name as shown in the preceding example.
 
An application should always check for a comma (,) to make sure only one
name has been returned. If the application needs only the driver name, and
not model information, it should parse the driver name and strip off text
beginning at the period.
 
Setting Job Properties
 
When an application has determined which printer driver to use, it can use
the default setting of the driver as the job properties or it can set the
job properties based on information the user stored with the document. In
either case, it can call the DevPostDeviceModes function to allow the user
to customize the print job.
 
The DevPostDeviceModes function causes the printer device driver to display
either a dialog box that allows the user to set job properties, or two
dialog boxes, one for job properties and the other for printer properties.
(Job properties apply only to the current print job; printer properties
change the default characteristics of the printer device driver. An
application should not change the system default printer, driver, or queue,
since these are set by the user.) The application should save with the
document any preferences entered by the user. An application can also use
DevPostDeviceModes to return the current job properties without displaying
any dialog boxes.
 
Printer Device Contexts
 
An application uses the queue and device driver data it retrieves from the
initialization files to open a device context for a printer. A device
context is a structure containing device-specific information. It acts as a
bridge between the presentation space in which an application produces a
document and the device that displays or prints the document. When an
application associates a presentation space with a screen device context,
output goes to the screen; when the presentation space is associated with a
printer device context, the output goes to the specified printer. A device
context for a printer is specific to a printer device driver and may include
information about customizing the print job. For more information about
device contexts, see the ◄Presentation spaces and device contexts► topic.
 
An application opens a device context for a printer by calling the
DevOpenDC function and passing it a pointer to a DEVOPENSTRUC structure.
Typically, the application specifies the contents of at least the first four
fields in DEVOPENSTRUC (the logical address, the printer-driver name, the
driver data, and the data type).
 
Types of Device Contexts
 
The second argument of the DevOpenDC function specifies the type of device
context to open. A device context for a printer can have type OD_QUEUED,
OD_DIRECT, or OD_INFO.
 
OD_QUEUED is the most common type of printer device context. This type of
device context takes advantage of the spooling capabilities of MS OS/2. When
an application uses this type, the spooler places print jobs into the print
queue. When the spooler determines that the printer is idle, the queue
processor either plays the metafile into the printer device context or
passes the job as raw data, depending on the data type specified in the
DEVOPENSTRUC structure. The printer device driver translates the output of
the queue processor into instructions that are meaningful to the printer.
Specifying OD_QUEUED allows an application to continue with other tasks once
the spooler has put a job into the print queue. Applications should use the
OD_QUEUED type of printer device context whenever possible.
 
An application might open an OD_DIRECT printer device context if it needed
to bypass the print queue (for example, when printing to a file) or if it
needed to perform drawing operations that the system does not support in
metafiles. For more information about metafiles, see the ◄Metafiles► topic.
 
An application can use the OD_INFO type to open a device context for
information only. For example, an application might use this device context
to determine the page size of the current printer; this information would
allow the application to provide on-screen pagination information.
 
Logical Address
 
The first field of the DEVOPENSTRUC structure is the pszLogAddress field,
which specifies the logical address for the device. The logical address of a
printer is the destination for the print data. Generally, this is the queue
the user has chosen──for example, LPT1Q. If the application is using a
driver that works with ASCII text rather than binary data (for example,
pscript.drv), it can direct print output to a file by specifying a filename
in this field.
 
Driver Data
 
The third field of the DEVOPENSTRUC structure is the pdriv field, which
points to a DRIVDATA structure that describes driver-specific aspects of the
page, such as the page layout (portrait or landscape) and the requested
paper form. Typically, an application specifies at least the device name and
structure size in the DRIVDATA structure, even if the application uses only
the default settings for a device driver, because many device drivers
support more than one device. If the driver supports only one device, an
application can set this field to NULL, causing the device driver to use the
default settings stored in os2sys.ini.
 
If an application uses the DevPostDeviceModes function to enable the user to
customize the print job, the third field of DEVOPENSTRUC points to the
buffer filled by DevPostDeviceModes; the application need not specify fields
in the DRIVDATA structure.
 
Data Type
 
The fourth field of the DEVOPENSTRUC structure is the pszDataType field,
which specifies the format of the print data. It can be PM_Q_STD or
PM_Q_RAW.
 
When an application specifies PM_Q_STD, the system records the effects of
Gpi functions in a metafile. Applications should specify PM_Q_STD whenever
possible, because this data format is more versatile and device-independent
than PM_Q_RAW. (If an application requires capabilities that metafiles do
not support, it cannot use PM_Q_STD. For more information about metafiles,
see the ◄Metafiles► topic.
 
When an application specifies PM_Q_RAW, the system performs the graphics
rendering immediately. The printer device driver creates a printer-specific
data stream and, if the type of the device context is OD_QUEUED, passes the
data stream to the spooler. Depending on the type of print job and the
driver, creating the spool file could be time-consuming, and the file the
driver produces could be very large.
 
Comment
 
The fifth field of the DEVOPENSTRUC structure is the pszComment field, which
contains a comment string that identifies the application when a print job
is displayed by Print Manager. Typically, the application name is used for
this comment. If the application specifies a string in the fourth parameter
of the DevEscape function, it should not specify a comment string in the
DEVOPENSTRUC structure.
 
Printer Device Contexts and Presentation Spaces
 
The DevOpenDC function returns a handle to a device context. An application
uses this handle in the call to the GpiCreatePS function that creates a
presentation space. When calling GpiCreatePS, the application can associate
the presentation space with the device context, by specifying GPIA_ASSOC in
the flOptions parameter.
 
When an application specifies GPIA_ASSOC in the call to the GpiCreatePS
function, it can specify zero as the width and height in the SIZEL structure
pointed to by the second parameter. The SIZEL structure contains the
dimensions of the presentation page, which defines how points in the
presentation space are mapped to the device. When the application specifies
zero for these dimensions, the system makes the presentation space large
enough to include one page, as defined by the device context.
 
The presentation-space type must be GPIT_NORMAL (not GPIT_MICRO) when an
application creates a presentation space for printing. If the application
specifies page units that are absolute measurements──for example,
PU_LOENGLISH or PU_HIMETRIC──graphics are the same size in printed output as
they are on the screen. If the application specifies PU_PELS, it must apply
transformations to the graphics to compensate for the different aspect
ratios and resolutions of the screen and printer.
 
An application can use the same presentation space for printing as it used
for drawing on the screen. Before the application can associate the
presentation space with a printer device context, the presentation space
must be disassociated from the previous device context. To do this, the
application calls the GpiAssociate function twice: the first time to
disassociate the presentation space with the original device context and the
second time to associate the presentation space with the printer device
context:
 
GpiAssociate(hpsWindow, (HDC) NULL);
    .
    .
    .
GpiAssociate(hpsWindow, hdcPrinter);
 
If an application uses the same presentation space for printing and window
drawing, it must process messages carefully in order to prevent conflicts
between what is displayed on the screen and what is printed. In particular,
the presentation space should not respond to a WM_PAINT message while
associated with a printer device context.
 
Once the application has associated a presentation space with a printer
device context, the application can use graphics functions to draw each page
of the document.
 
Printing Documents
 
Drawing for printing is similar to drawing in a window the size of a piece
of paper. If an application uses device-independent world units to produce
graphics, the system automatically scales the output so that the graphics
will look the same on any output device; a one-inch circle drawn on the
screen is printed as a one-inch circle on a 72-dot-per-inch impact printer
or on a 300-dot-per-inch laser printer. For more information on scaling
graphics, see the ◄Coordinate Spaces and Transformations► topic.
 
Starting a Print Job
 
Before an application starts drawing graphics in a printer device context,
it must use the DevEscape function to issue a DEVESC_STARTDOC escape.
DevEscape allows an application to send an escape directly to a device
driver──in this case, the escape function tells the printer device driver
that the printer should be prepared to print a document.
 
Determining Printer Capabilities and Page Size
 
An application can use the DevQueryHardcopyCaps function to determine the
capabilities of the printer associated with the printer device context.
DevQueryHardcopyCaps fills one or more HCINFO structures with detailed
information about the page type and page dimensions supported by the device.
Each HCINFO structure also specifies whether the described configuration is
currently selected for that device. For example, an application could call
DevQueryHardcopyCaps to fill five HCINFO structures with information about a
printer. If the printer supported Letter paper, Legal paper, Landscape
paper, Wide paper, and A4 paper, the dimensions of each of these "form
names" would be specified, and one of them would be designated as the
current choice for that printer.
 
DevQueryHardcopyCaps returns the dimensions of a page in millimeters. If the
drawing units in an application's presentation space are absolute values in
world space (metric or English), determining the page boundaries in the
presentation space requires only a simple conversion.
 
An application could also use the DevQueryCaps function to retrieve the
width and height of the printer page in device units. The page size returned
reflects either portrait or landscape mode, depending on what the user has
selected. To convert device units into world coordinates, the application
can call the GpiConvert function.
 
Printing a Page
 
Each page of a print job is drawn by using Gpi functions in a presentation
space that has been associated with a printer device context. If a document
consists of only one page, the origin of the presentation space's coordinate
system typically corresponds to the origin of the device page, so no
translation is necessary. To print a multiple-page document, however, an
application must translate the world-space coordinates of the presentation
space so that a point defining the lower-left corner of the graphic to be
printed corresponds to the origin of the device page.
 
An application can determine the best places to divide a large image by
using the page size retrieved by the DevQueryHardcopyCaps or DevQueryCaps
function. After establishing the page boundaries, the application moves each
page to the origin of the coordinate space, calls the DevEscape function to
start a new page, and draws the image. To move a page to the origin of the
coordinate space, the application calls the GpiQueryDefaultViewMatrix
function to fill a MATRIXLF structure with the current transformation
values, sets a POINTL structure to values based on the page size and passes
a pointer to that structure to the GpiTranslate function, and then calls the
GpiSetDefaultViewMatrix function to set the new viewing matrix. For more
information about coordinate spaces and transformations, see the
◄Coordinate Spaces and Transformations► topic.
 
To start a new page in a multiple-page document, an application must call
the DevEscape function at the end of each page, specifying the escape
DEVESC_NEWFRAME. (The application need not send a DEVESC_NEWFRAME escape
after the last page in a document.)
 
Finishing a Print Job
 
After printing every page in a print job, an application must call the
DevEscape function, specifying the DEVESC_ENDDOC escape.
 
Printing in a Thread
 
Printing typically begins when a user chooses a command from a menu in an
application. A client window receives a WM_COMMAND message from the menu and
begins the printing operation. The application does not process any further
mouse clicks or keystrokes until it calls the WinGetMsg or WinPeekMsg
function again. This means that the user cannot interact with the printing
application or switch to another application until one of these two
functions is called. If the application is not using the spooler and queue
processor, or if the print job is lengthy or complicated, the user may have
an inconvenient wait before being able to resume work.
 
There are two common methods for allowing an application to remain
responsive during a lengthy printing operation:
 
♦  The application can handle user input by calling the WinGetMsg or
   WinPeekMsg function.
 
♦  The application can create a separate thread to handle printing. The main
   thread can continue to call the WinGetMsg function while the printing
   thread is running.
 
Although printing in a thread is the most common way of solving this
user-interface problem, handling user input during printing can cause
problems with data integrity and synchronization. (For example, a user could
attempt to modify a document while it is printing.) An application could use
semaphores to protect shared resources whenever there are potential
conflicts.
 
Processing WM_PAINT messages is a common problem for applications that print
in a thread and that use the same presentation space for both drawing on the
screen and printing. An application should not attempt to draw in the window
when the presentation space is associated with a printer device context.
 
Printing Bitmaps
 
An application must perform the following steps to print a bitmap:
 
1  Create a device context and presentation space for the printer.
 
2  Create a memory device context for the printer and associate it with a
   presentation space. This memory device context should be compatible with
   the printer device context.
 
3  Create a bitmap in (or load it into) the printer's memory presentation
   space.
 
4  Attach the bitmap to the printer's memory presentation space and device
   context by calling the GpiSetBitmap function.
 
5  Draw the bitmap from the printer's memory presentation space and device
   context to the printer presentation space and device context by using the
   GpiBitBlt or GpiWCBitBlt function. Do any scaling necessary to correct
   for resolution differences between the display and the printer.
 
The GpiSetBitmap function converts between different device formats──for
example, color to monochrome──but does not correct for differences in pel
resolution between devices. For example, if an application prints a screen
bitmap (typically about 72 pels per inch) to a laser printer with 300 pels
per inch, it must scale the image when converting from the printer's memory
device context to the device context. The application can determine the
device resolutions by calling the DevQueryCaps function for each device.
 
Metafile Restrictions
 
Most applications record print jobs as metafiles, which the queue processor
plays into the printer device context when the spooler determines that the
printer is idle. Although metafiles are versatile and device-independent,
some restrictions apply to their use. If an application can use metafiles in
printing, it specifies PM_Q_STD in the DEVOPENSTRUC structure when opening
the device context. If the application cannot use metafiles, it specifies
PM_Q_RAW.
 
An application should not change any of the following items while drawing in
a metafile:
 
♦  The graphics field.
 
♦  The code page for the default character set.
 
♦  The color table. (The size of the color table must not exceed 31K.)
 
♦  The default viewing transformation.
 
♦  The setting of the draw controls. (The DCTL_DISPLAY flag in the
   GpiSetDrawControl function must be on.)
 
♦  The default values of attributes, viewing limits, primitive tags, and arc
   parameters.
 
An application should not call the following functions while drawing in a
metafile that will be played in a printer device context:
 
♦  DevEscape (for an escape that is stored in a metafile)
 
♦  GpiDeleteSetId
 
♦  GpiErase
 
♦  GpiExcludeClipRectangle
 
♦  GpiIntersectClipRectangle
 
♦  GpiOffsetClipRegion
 
♦  GpiPaintRegion
 
♦  GpiResetPS
 
♦  GpiSetClipRegion
 
♦  GpiSetPel
 
♦  GpiSetPS
 
Because an application should not call the GpiDeleteSetId function when
using metafiles for printing, local identifiers cannot be reused inside a
print job. If an application uses a bitmap in a GpiWCBitBlt operation or as
an area-fill pattern, the application should not modify the bitmap.
 
Applications should not reassociate the presentation space while it is
associated with an OD_QUEUED device context.
 
An application should use only these foreground mix modes when using a
metafile for printing:
 
♦  FM_DEFAULT
 
♦  FM_LEAVEALONE
 
♦  FM_OR
 
♦  FM_OVERPAINT
 
An application should use only these background mix modes when using a
metafile for printing:
 
♦  BM_DEFAULT
 
♦  BM_LEAVEALONE
 
♦  BM_OVERPAINT
 
An application that is using a metafile for printing can use the following
escapes in calls to the DevEscape function:
 
    DEVESC_ABORTDOC
    DEVESC_BREAK_EXTRA
    DEVESC_CHAR_EXTRA
    DEVESC_DRAFTMODE
    DEVESC_ENDDOC
    DEVESC_FLUSHOUTPUT
    DEVESC_GETSCALINGFACTOR
    DEVESC_NEWFRAME
    DEVESC_NEXTBAND
    DEVESC_QUERYESCSUPPORT
    DEVESC_QUERYVIOCELLSIZES
    DEVESC_RAWDATA
    DEVESC_STARTDOC
 
An application that is using a metafile for printing should not use the
following escapes in calls to the DevEscape function:
 
    DEVESC_DBE_FIRST
    DEVESC_DBE_LAST
    DEVESC_GETCP
    DEVESC_SETMODE
    DEVESC_STD_JOURNAL
 
 
                                      ♦