Accept also PCLm as a PDL for driverless printing (used by Mopria and Wi-Fi Direct printers)

[tillkamppeter]

To complete driverless printing support so that all 4 driverless printing standards (AirPrint, IPP Everywhere, Mopria, Wi-Fi Direct) get full supported the only missing of the 4 driverless PDLs (PDF, PWG Raster, Apple Raster, PCLm) is PCLm.
Shortly after the last OpenPrinting Summit 2017 I have found the specs of the PCLm data format and let a Google Summer of Code student implement this. He succeeded and now cups-filters (1.17.2 or later) contains a rastertopclm filter to generate PCLm.
With this it should now be easy to add PCLm support to CUPS by accepting PCLm as a driverless printer PDL and adding the needed parts to the PPD generator in cups/ppd-cache.c.

[tillkamppeter]

Here is the PPD generator patch of Issue #5091 with PCLm support added:
ppd-generator-resolution-quality-pclm.patch.txt
Note that not only a "*cupsFilter2" line for PCLm gets added (if PCLm does not disqualify to to a broken or missing attribute for its resolutions) but also all "pclm-..." IPP attributes get put into the PPD file as "*cupsPclm..." lines. These lines are needed by the rastertopclm filter in order to generate the correct PCLm format for the particular printer.
Note that this does not contain the needed modifications in CUPS so that a DNS-SD-advertised printer is considered as supporting driverless printing if it supports PCLm as one of its PDLs.

[michaelrsweet]

I think the PCLm stuff will need to stay as a fork - we have no plans to support it in macOS and I personally see no point in supporting it when all PCLm printers also support Apple or PWG Raster...

[tillkamppeter]

Is there a standard telling that if a printer supports PCLm then it has to support one of the others? Or is it simply an observation?

[michaelrsweet]

It is a simple observation - all Wi-Fi Direct printers (Wi-Fi Direct Print services is the only standard calling for PCLm) also support AirPrint, which requires Apple Raster.

[tillkamppeter]

I do not want to convince you to add PCLm support, but Mopria calls for PCLm, too.

[michaelrsweet]

Mopria is not a standards organization, and they call for PCLm because Wi-Fi Direct Print Services calls for it. Mopria also calls for IPP Everywhere, which requires PWG Raster and says nothing about PCLm.