“About routeprint” discusses the routeprint command, which converts files into printable form.
“Converting a File for Printing” explains how the Desktop converts a file for printing.
“The Print Conversion Rules” explains the print conversion rules.
“The Current Printer” discusses the Desktop's concept of the current, or default, printer and the Desktop environment variable $CURRENTPRINTER.
This chapter explains the process routeprint uses to convert data files into a printable format, what file types routeprint already recognizes, and how to write your own print CONVERT rule to allow your application to tap into routeprint's powerful printing capabilities.
The Desktop already has rules for printing many types of files, such as ASCII, PostScript, and RGB image files. The easiest method for printing a file of arbitrary format is to break down the printing process into small, modular steps.
For example, instead of writing dozens of specialized rules to print reference pages directly for each kind of printer, you can instead convert reference pages to nroff format and then convert the nroff format to the format required for the current printer.
The diagram shown in Figure 14-1 illustrates the steps by which some of the supported Desktop file types are converted for printing. Each box represents one or more file types; the arrows between them indicate the steps by which the file types are converted. The values associated with the arrows represent the cost of the conversion. This concept is talked about more in “Print Costs” later in this chapter.
This modular approach to printing has two major advantages:
The modular steps are reusable. Because you can reuse each modular printing step, you write fewer rules.
routeprint can pick the most efficient route for printing. There is often more than one sequence of conversion steps to print a file. routeprint chooses the sequence of steps that provides the best possible image quality.
This modular, multi-step conversion to printable form is called the print conversion pipeline, a series of IRIX commands that process a copy of the file's data in modular increments. The print conversion rules are designed to take advantage of this method of processing printable files.
In addition, applications or software packages can add new arcs to the CONVERT rule database whenever they define new types or have a better way of converting existing types. For example, Impressario includes a filter to go directly from NroffFile to PostScriptFile—this new filter has a lower cost than the default conversion, which goes from NroffFile to Ascii to PostScriptFile.
The Desktop already has rules for printing a large number of file types. You can use grep to list all of these print conversions definitions by typing:
% grep -i convert /usr/lib/filetype/*/*.ftr
|Note: The list of print conversion definitions generated by the above command is long and unsorted.|
Frequently, there is more than one set of steps that routeprint can use to print your file. To compare different ways of printing a file of a particular type, routeprint associates cost numbers with each conversion, then chooses the series of conversions with the lowest total cost. The cost of a conversion represents image degradation and processing cost, and is specified by a number between 0 and 1000 inclusive. The higher the cost of a conversion, the more routeprint attempts to avoid that conversion method if it has alternative methods.
The conventions for determining the cost assigned to a given conversion are described in Table 14-1.
Equivalent filetypes, or a SETVAR rule (described in “The Print Conversion Rules”
Default conversion cost
Trivial data loss, or conversion is expensive
Minor data loss, but conversion is not expensive
Noticeable data loss and conversion is expensive
Obvious data loss (for example, color to monochrome)
the CONVERT rule
the COST rule
the FILTER rule
source-type-name is the file type you are converting from. destination-type-name is the file type you are converting to.
CONVERT NroffFile PostScriptFile
Do not use the convert rule to convert directly to a new printer type; convert to a standard Desktop file type instead. Silicon Graphics reserves the right to alter printer types, so converting to a standard file type (for example, PostScriptFile) is a more portable solution. Appendix E, “Predefined File Types”, lists some of the file types defined by Silicon Graphics. You can generate a complete list of file types installed on your system using the grep(1) command:
% grep TYPE /usr/lib/filetype/*/*.ftr
|Note: The list of file types generated by the above command is very long and unsorted.|
The non-negative-integer represents the arc cost, or incremental cost of the conversion. This cost is used to reflect processing complexity or can also be used inversely to reflect the output quality. When routeprint selects a conversion sequence, it takes the arc costs into account, choosing the print conversion sequence with the least total cost. It is highly recommended that you specify a COST rule. If you omit it, routeprint assumes the cost of the conversion is zero, which may cause routeprint to return an inappropriate print conversion pipeline. The default cost is 50.
The FILTER rule represents part of an IRIX pipeline that prepares a file for printing. filter-expression can be any single IRIX command line expression, and generally takes the form of one or more piped commands. In the general case, the first command within a single FILTER rule receives input from stdin; the last command in the rule sends its output to stdout. routeprint concatenates all the FILTER rules in the print conversion pipeline to form one continuous command that sends the selected file to its destination printer.
There are three special cases in creating FILTER rules:
In a “first” case rule, the FILTER rule is the very first rule in the print conversion pipeline. In this case, routeprint passes the list of selected files to the first command in the FILTER rule as arguments. If a first case FILTER rule begins with a command that does not accept the files in this fashion, prepend the cat command to your rule:
FILTER cat | tbl - | psroff -t
The files will then be piped to the next command's stdin.
In a “last” case rule, the FILTER rule is the very last rule in the print conversion pipeline. This rule contains a command that sends output directly to a printer (such as lp). Last-case rules are already provided for many file types. To ensure compatibility between your application and future printing software releases, you should refrain from writing your own last-case rules. Instead, write rules that convert from your file type to any of the existing file types, and let the built-in print conversion rules do the rest.
In a “setvar” case rule, the FILTER rule is used to set an environment variable used later in the print conversion pipeline. The first CONVERT rule in the example below sets a variable that defines an nroff macro used in the second rule. In all setvar cases, stdin is passed to stdout transparently. Thus, you can include setvar as part of the pipeline in a single FILTER rule.
CONVERT mmNroffFile NroffFIle
FILTER setvar MACRO=mm
CONVERT NroffFile PostScriptFile
FILTER eqn | tbl | psroff -$MACRO -t
The current printer is the system default printer that the user sets with the Print Manager or, alternatively, the printer specified by the -p option to routeprint. If no default is set and -p is not used, an error message is returned by routeprint to either stdout or a notifier window (if the -g option to routeprint was set). The Desktop environment variable $CURRENTPRINTER is set to the currently selected default printer.