Host-resident font downloads

When the PostScript document contains a request for fonts not loaded on the printer, the download filter manages this request.

The download filter is invoked as a fast filter; it downloads fonts automatically if the fonts reside on the same system as the printer. The download filter may also send fonts to a remote printer. To do this, you can create a new filter table entry that calls the download filter as a slow filter through the -y option. Alternatively, you may force selection of this filter by changing the input type.

The download filter does the following:

• It searches the PostScript document to determine which fonts have been requested. These requests are documented with the following PostScript structuring comments in the header comments:

    %%DocumentFonts: font1 font2 . . .

• It searches the list of fonts resident on that printer (in /etc/lp/printers/printer-name/residentfonts) to see if the requested font must be downloaded.
• If the font is not resident on the printer, it searches the host-resident font directory to see if the requested font is available. The only candidates for downloading are fonts listed in the map table that point download to readable files. A Type 1 font is downloaded once, at most, for a single document, even if it occurs multiple times in the %%DocumentFonts: comment or PostScript file. The downloading of fonts occurs only for the duration of the PostScript job. However, permanent downloading of fonts to the printer's RAM can be done with special PostScript programming techniques using the exitserver operator.

  Requests for unlisted fonts or inaccessible files are ignored. All requests are ignored if the map table cannot be read.

• If the font is available, the filter takes the file for that font and prefixes it to the file to be printed.
• The filter sends the font definition file and the PostScript source file (the file to be printed) to the PostScript printer.