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Re: Apple raster, PWG raster and non-free filters/drivers

On 01/16/2017 05:17 PM, Brian Potkin wrote:

My question is here whether the Google Cloud Print server polls printer
capability info from the printer or whether it has a database with info
about thousands of printer models? In the latter case we do not have
driverless printing here and a GCP printer has its model capabilities in
Googles database, in addition to understanding one of PWG Raster and PDF.

I do not know whether any sort of a database is used, but suspect not.


During the registration phase the capabilities are obtained. I can only
connect a classic printer and have seen the PPDs of the queues being
uploaded (over an XMPP/https connection, I suppose). The downloaded file
for a job is a PDF.

How I understand it now is that a GCP 2.0 printer when registering sends a CDD record with its capabilities to the server, so there really seems to be no database with printer-model-specific data on the server and so we have really driverless printing.

Your "classic" printer is probably not registering itself, but on your computer is a CUPS queue with PPD and driver and the registering process (Chrome/Chromium browser) is registering your CUPS queue sending the queue's PPD file. It is nor problem to register CUPS queues as they have a PPD and they accept jobs in PDF.

Now if you want to use a printer whose only driverless mode is GCP 2.0 directly with your computer, without the internet or Google Cloud Print in between, you would need a way to poll the CDD record from the printer (the format is documented by Google), but I do not know how to do this, whether there is a standard way to do it, or whether it is possible at all. In the worst case you will need to make your computer emulating a Google Cloud Print server. Google probably provides enough information to do so, but it would be a high effort to get this class of printers supported.

So the fact that a printer is a GCP printer only helpos for driverless
printing if Google can actually poll the printer's capabilities from the
printer and if Google publishes the protocol for this kind of poll.

The Chromium browser (and Chromebooks, I believe) can do driverless
printing through GCP from the point of view of the user.

This would mean that even for local printing you need to be connected to the internet.

The technique
does not involves CUPS. I understand the significance of the term
"driverless printing" when applied to CUPS+cups-filters+cups-browsed
but, at the same time, it is quite a well-used and general term whose
implementation depends on the service being used.

I understand "driverless printing" as, first, not needing any software or data which is specific to the printer model on the computer (the "printer driver"), in order to use the printer, and second, only data and not code to be executed on the computer be polled from the printer in order to use it.

This way you can simply connect the printer to a computer with any arbitrary operating system and you can just print, without needing to install something or even being restricted to certain operating systems.


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