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OpenPrinting developer resources

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The cups-filters project at OpenPrinting (included in all Linux distributions using CUPS 1.6.x or newer) provides the filters needed to convert the print job output of desktop applications (usually PDF) into the printer's native language or into the universal CUPS/PWG-Raster format as input for a separate printer driver. It also provides the pdftopdf filter to apply page management (N pages per sheet, selected pages, even/odd pages for manual duplex, mirror for iron-on sheets, …) to the PDF data stream.

A central part to make this work is a PDF renderer and many of the filters are simply wrappers about a PDF renderer. Currently, cups-filters supports Ghostscript and Poppler as PDF renderer. With this project we want to add support for MuPDF as it is a more lightweight renderer made by Artifex, the printing specialists who already made Ghostscript. This is especially interesting for mobile devices with limited meomory, mass storage, and CPU resources.

The student will have to modify all filters which need a PDF renderer (pdftops, pdftoraster, pdftoijs, pdftoopvp, perhaps also pdftopdf) to add support for MuPDF without dropping the existing support for Ghostscript and Poppler. Switching between the renderers should be able at run time, to make binary packages of cups-filters suitable for systems of different form factors.

Mentors: Till Kamppeter, OpenPrinting Manager, The Linux Foundation (till at linux dot com), Tobias Hoffmann (smilingthax at googlemail dot com), MuPDF developers TBD

Desired knowledge: C and/or Cprogramming Code License: MIT, GPL =====Add printer output backends to MuPDF===== MuPDF is a lightweight PDF renderer made by Artifex, the company behind Ghostscript. In contrary to Ghostscript, MuPDF is a pure PDF renderer. It does not contain a PostScript interpreter nor parts of it are written in PostScript. This makes it smaller, faster, and less resource-consuming, the ideal solution for mobile devices like tablets or smartphones. On mobile devices printing will not be done with having tons of printer-model-specific drivers on the system. Once, they consume the limited mass storage space, and second, one uses the mobile device in several different local networks with different printers: At home, in the office, in a copy shop, ... and one wants to use the printers which are available there, without installing drivers and setting up queues. Therefore we want to have a system which automatically detects network printers and makes them available for local apps. To do so we restrict ourselves to printers with known, common languages: IPP Everywhere (Upcoming standard, PWG Raster and optionally some others) and PostScript, PDF, PCL 5c/e/6/XL (legacy standards). So MuPDF has to generate raster output for these languages, meaning raster embedded in the specifics of the language, and to avoid exhausting printer resources raster in small bands and no high-level output, even if the printer language is high-level. Artifex will also work on this, but to get additional man power we are also opening this project for students. Note that you have to assign copyright on your code to Artifex, as otherwise the code cannot be integrated in MuPDF. This project can be split to be worked on by more than one student. Mentors: MuPDF developers TBD, Till Kamppeter, OpenPrinting Manager, The Linux Foundation (till at linux dot com) Desired knowledge: C and/or C++ programming Code License: GPL =====Improve the pdftopvp filter to not need copying Poppler source code or unstable APIs===== The cups-filters project at OpenPrinting (included in all Linux distributions using CUPS 1.6.x or newer) provides the filters needed to convert the print job output of desktop applications (usually PDF) into the printer's native language or into the universal CUPS/PWG-Raster format as input for a separate printer driver. It also provides the pdftopdf filter to apply page management (N pages per sheet, selected pages, even/odd pages for manual duplex, mirror for iron-on sheets, ...) to the PDF data stream. One of the filters is pdftoopvp which is the interface between PDF (the standard print job format under Linux) and the OpenPrinting Vector high-level printer driver interface standard. This standard is currently used by several Japanese-market laser printers which do not use PostScript as it is usual in Europe and the US. This filter currently only supports Poppler as PDF renderer and the connection between the filter and Poppler is rather awkward, copying parts of Poppler's source code and using unstable APIs of Poppler which change with newer Poppler versions. This makes maintaining the filter difficult for the Linux distributions. The task for the student is here to once improve the interface with Poppler if possible and also add support for Ghostscript (would improve color management a lot) and MuPDF (would improve integration with mobile and embedded devices). Mentors: Till Kamppeter, OpenPrinting Manager, The Linux Foundation (till at linux dot com), Koji Otani, BBR Inc. Japan (sho at bbr dot jp) Desired knowledge: C and/or C++ programming Code License: MIT =====PWG Job-Ticket backend for libJTAPI (Job Ticket API)===== Job tickets are extended descriptions for print jobs. They tell which documents should be printed, on which type of paper, which resolution and quality, whether there should be sheets inserted between the documents, ..., and even information like delivery address, payment, ... A job ticket accompanies a print job from its submission to its delivery. Job tickets come from the professional printing world. In former times they were a paper form with instructions what everyone involved in the printing process has to do. Nowadays they are standardized files which are used by print servers, printers, and production printing machines. IPP Everywhere is a next generation printing protocol by the Printing Work Group (PWG) and uses job tickets for all printing metadata. This makes job ticket handling vital for IPP Everywhere support. For IPP Everywhere the PWG has created the [[ftp://ftp.pwg.org/pub/pwg/candidates/cs-sm20-pjt10-20120801-5108.07.pdf PWG Job Ticket format]]. Libjtapi is OpenPrinting's reference implementation of the FSG's JTAPI standard. The FSG (Free Standards Group) was a predecessor to the Linux Foundation. The JTAPI standard defines an abstract api for producing and consuming job tickets. Thus Libjtapi can create Job Tickets and translate between job ticket formats provided a backend has been developed. This project is to develop a Libjtapi backend for the PWG's job ticket format. This backend should be able to consume PWG tickets and produce PWG tickets. Proposed Tasking: Objective: Develop a Libjtapi backend for accepting, parsing, interpreting and translating PWG Job Tickets to LibJTAPI objects/attributes. Approach: As Libjtapi is written in C89 this backend should be as well. PWG Job Tickets can come in either XML or JSON flavours and only one of these flavours must be supported. A JSON or XML parsing library written in C89 and relicensable under the EPL should be used. The backend may be written using internal Libjtapi helper functions or against the more verbose jtapi apis. Code License: EPL Coding Language: C89 Coding Document: In-line commenting must be sufficient to understand the flow and any section requiring extended understanding. Operating System: Student’s choice – Linux, Windows, Mac, … (non-gui for either) Interface: Command Line Document: Minimum: - How to build the PWG Job Ticket backend. - How to build the test suite - How to run the test suite - Three example PWG job tickets that can be consumed and produced without data loss. Mentor: Glen Petrie, Epson (glen dot petrie at eitc dot epson dot com) Desired knowledge: C Programming   =====foomatic-rip: Replace the universal print filter by an easy-to-maintain CUPS filter===== foomatic-rip is a universal print filter to work as a wrapper around Ghostscript to make the use of Ghostscript-based printer drivers with arbitrary printing systems simple. In the times back when the Foomatic project started there were many printing systems available for Linux: LPD, GNUlpr, LPRng, CUPS, PDQ, PPR, CPS, … and they were all supported by Foomatic. Currently practically only CUPS is used and CUPS is also the only printing system with ongoing development and solid maintenance. The other systems are not maintained and developed any more (only very little activity on LPRng) and only rarely used. The idea is to make a replacement for the foomatic-rip filter which supports only CUPS and drops all the code for the other printing systems which gets only rarely used and therefore very difficult to maintain and test. The remaining code should also simplified as much as possible to get best maintainability. Mentors: Lars Uebernickel, printing software developer (lars at uebernic dot de), Till Kamppeter, OpenPrinting Manager, The Linux Foundation (till at linux dot com) Desired knowledge: C and/or C programming

Code License: GPL

Foomatic serves now well for more than 10 years for integrating Ghostscript-based printer drivers with the printing environment under Linux (usually CUPS). Based on an XML database of printers, drivers, and user-settable driver options PPD (Postscript Printer Description) files are generated and used together with the universal print filter foomatic-rip. This way the user has access to all the driver's (and printer's) capabilities and Ghostscript is correctly called by the printing system to execute the print job.

This worked principally very well. One can really control all options of the printer drivers and even more sophisticated techniques, like CUPS' custom options (arbitrary numbers and strings as parameters) are supported.

But there are still two problems which did not get addressed due to the lack of manpower for implementing them:

Option setting conflicts

Often option settings do not work together, like printing double-sided on transparencies. PPD files use the “*UIConstraints: …” keyword to mark these conflicts so that in print dialogs and printer setup tools one cannot choose conflicting settings.

Foomatic has no functionality to define option setting conflicts and generate appropriate “*UIConstraints: …” keywords in the PPD files.

Printer compatibility classes

The other problem is that it is rather awkward to assign drivers and options to printers if there are very many similar, compatible models. Often one has to mention each printer explicitly in the driver and option XML entries.

Instead of needing to add many compatible printers to the drivers and to the constraints of options one could introduce compatibility classes. A compatibility class contains absolutely compatible printers, which means printers which work with the same drivers, the same options, and the same choices for the options. Then one can put the class name into the list of supported printers of a driver and also into the constraints of the options and so one avoids needing to insert tenth of printers everywhere. Especially there are many HP inkjets which are absolutely compatible to each other (around ten classes instead of 100 printers) and there are many clones of HP LaserJet printers.

What is needed for solving both problems is an extension to XML database, to the SQL representation of the database (for accelerated database access), and to the PPD file generator.

Mentor: Till Kamppeter, OpenPrinting Manager, The Linux Foundation (till at linux dot com)

Desired knowledge: Perl programming

Code License: GPL

In the free software world there are often several different projects for fulfilling the same task. For rendering (rasterizing) PDF (the standard format for print jobs) there are Poppler and Ghostscript. Both have there advantages and disadvantages, for example Poppler is completely written in C++ whereas the PDF interpreter of Ghostscript is written in PostScript (note that PostScript is a full-featured programming language), which makes Poppler smaller and faster. Ghostscript's advantage is having better color management and being better optimized for printing.

Unfortunately, one cannot freely choose between the two yet as Ghostscript has many important printer driver, especially “pxlcolor”/“pxlmono”, built in and so dropping Ghostscript in favor of Poppler would lead to a loss of important functionality, like PCL-XL printer support.

To avoid this we need to make all printer drivers working with arbitrary renderers. This is easy to implement for most modern drivers which are IJS plug-ins, separate filters, CUPS raster drivers, and OpenPrinting Vector drivers, but for the drivers built into Ghostscript this is not yet possible.

Therefore we want to modularize the built-in Ghostscript drivers into something which plugs into the renderer. A side effect of this is also the easier maintainability of Ghostscript and of the drivers, especially of built-in drivers from third parties.

As there are some high level/vector devices the suggested interface is the OpenPrinting Vector framework. The implementation should be some kind of glue code module which has on one end the OPVP interface to get the data from the renderer and on the other end the internal API of GhostScript to couple to the original GhostScript driver code. Compiling this should result in one or more OPVP drivers with the same functionality as the built-in GhostScript drivers.

Goal of this project is to implement and test this framework and it would be a plus to also do the needed modification of the Foomatic data to generate the PPDs for the modularized drivers.

Mentor: Hin-Tak Leung (HinTak dot Leung at gmail dot com), author of several drivers for printers with proprietary protocols; Till Kamppeter, OpenPrinting Manager, The Linux Foundation (till at linux dot com)

Desired knowledge: Knowledge in C programming is required. Great is also knowledge in PostScript and the Linux/Unix printing workflow.

Code License: GPL

There was a Google Summer of Code 2007 project under wine [1] to use WIN32 drivers to print from wine, and some adaption of that idea in some limited fashion in ddiwrapper [2]. It would be quite interesting and useful to properly integrate this into the more general printing workflow:

• make it possible to print from linux applications through cups or other spoolers with more(all?) WIN32 drivers

Currently there are two(?) frameworks which are usable for loading binary-only closed-source vendor driver modules, OPVP and IJS. There are a few other FOSS projects which uses some part of wine to load binary-only WIN32 modules for accessing data in proprietary format quite successfully - e.g. ndiswrapper (for wireless network hardware), mplayer (for multimedia playback).

Some background information is in [3]

Mentor: Hin-Tak Leung (HinTak dot Leung at gmail dot com), author of several drivers for printers with proprietary protocols; Detlef Riekenberg from the Wine Project, who was the mentor for the Gsoc 2007 wine project for print proxy, has agreed to be involved.

Desired knowledge: C programming

Code License: GPL/LGPL/Public Domain

Since four years the OpenPrinting web site uses a PHP/MySQL based web application to administer a growing printer and printer driver database. Currently the site supports searching and listing of printers and drivers, download and submission of PPD (Postscript Printer Description) and drivers and a rudimentary backend interface for moderation of submissions.

While all basic functionality is given, there are a lot of areas to improve. The long forms related to driver and printer submission could be shortend and moved to an assistant that allows for an easier and faster submission process. The moderation process could be simplified to allow an even faster overview for moderators and administrators. There are a lot of small issues where usability could be enhanced, for example links to create a similar printer, duplicating an existing record.

The backend processing is another part that should be improved. Currently all scripts and build routines of the project are mostly tight to server environment that serves the web site. Beside building more generalized scripts, the student could also automate the import and update process of Printer Description files in the exisiting BZR repository.

Basic email notifications for administrators and moderators exist, but optional notifications for uploaders are still missing.

There is still a lot of manual work involved, that could be simplified or automated to leave more time to contributors and administrators to work in drivers and printer descriptions itself.

Mentors: Till Kamppeter, OpenPrinting Manager, The Linux Foundation (till at linux dot com), Jeff Licquia, The Linux Foundation (jeff at licquia dot org)

Desired knowledge: PHP, MySQL, web interface programming, (Bash) scripting, basic usability experience Code

License: GPL

Adrian Johnson did a lot of the work needed to make cairo color managed. Finishing this work and getting the code upstream would allow us to simplify a lot of applications that use cairo. See http://cgit.freedesktop.org/~ajohnson/cairo/log/?h=color-space for the branch. Adrian has also patched Inkscape to use the new features, and that needs cleaning up and pushing upstream http://cgit.freedesktop.org/~ajohnson/inkscape/log/?h=color-space Also see http://lists.cairographics.org/archives/cairo/2012-July/023353.html and https://mail.gnome.org/archives/gimp-developer-list/2012-August/msg00084.html for more details.

Expectations: The cairo and inskcape code is pushed upstream with any required modifications. Ideally someone familiar with the cairo community would take this on, as Adrian found it hard to get the code approved upstream.

Skills: Understanding of basic color management, basic use of bzr and git, proficient in C.

Contact: Richard Hughes