Writing a printer driver in JavaScript

Writing a printer driver in JavaScript(kubesail.com)

103 points by pastudan 4 years ago | 17 comments

notpachet 4 years ago |

As someone who has spent an unfortunate amount of time working on shipping label software for ecommerce companies, my advice is to stay the hell away from ZPL. It's the layout language equivalent of C -- too many low-level footguns. Just send 4x6 PDF's to your thermal printer and be done with it. There are so many more tools, of much better quality, available for composing PDF's than you'll ever find for ZPL or other vendor-specific layout languages.

Sure, if you know you're always going to be using a Zebra printer, and you control the whole pipe from software to the physical label, then you're going to have a lot more explicit control if you use ZPL over a PDF. But the second any of those presuppositions change, it's back to the drawing board. (Actually, even the Zebra assumption isn't sound, because they themselves are not always 100% reliable in following their own specifications. And the specifications... boy howdy.)

The old argument in favor of ZPL is that you can be much more precise with the instructions you're sending to your thermal, resulting in higher print quality, and therefore more reliable barcode scans and OCR. But the world doesn't stand still, and shipping carriers have been steadily improving their scanning capabilities over the last 20 years, even while thermal printer capabilities have remained largely stagnant. After all, USPS has to also optimize for people who are printing labels on shitty desktop inkets. The increase in barcode quality you'd get out of using ZPL is overkill.

TLDR: Save yourself a lot of heartache and just sling PDF's. Postscript/Ghostscript is so much easier to cajole into cooperation.

tcas 4 years ago | |

As someone who's dealt with these protocols as well I agree.

I find the print quality of PDFs perfect on Zebra's as long as you keep the following in mind:

  - Make sure the DPI of the document is correct (e.g. 203dpi)
  - Make sure the document does not need to be scaled (and scaling to fit is disabled) (for 4x6 that means 812 x 1218 pixels max)
  - Make sure the document is black and white (no grayscale)

ZPL is a beast.

Some PDFs embed a single image in them, in which case you can do the following;

  pdfimages -all <input_file>.pdf <out_prefix>
  convert <generated_png>.png -filter point -density 203 -units PixelsPerInch out.png

And then print the generated png.

pastudan 4 years ago | |

Completely agree. I tried scaling down the PDFs but Ghostscript on the Raspberry Pi is far slower than just scaling the 1200px wide PNG to 800px. I still got very readable barcodes, and a 100% delivery rate on my first batch of orders, even with that downsampling.

I could be wrong, but I don't think pixel perfect barcodes are necessary with modern scanners. The only thing going for ZPL is the ability to store the label data as simple ASCII text.

kayodelycaon 4 years ago | | |

Did you try using imagemagick to convert to the pdf?

eyelidlessness 4 years ago | |

Heck, if:

- you can target PDF

- you’re married to a JS stack

- your motivation is (quoting the article)

> When you purchase a shipping label through them, they give you the output in either a PDF, PNG, or ZPL format. ZPL would be ideal, since it's just ASCII text which can easily be modified, or even stored in a database along side each order.

It seems like a much more reasonable intermediate format is SVG or JSX, both of which have mature to-PDF solutions, and both of which have much more well-known manipulation stories. Of course, that doesn’t lead to an absolutely bonkers blog title like this. But for anyone considering a similar setup, there are much more conservative options.

jhallenworld 4 years ago |

It's amazing how old ZPL is. I wrote a Zebra-140 driver (in C..) in something like 1993.

https://github.com/jhallen/joes-sandbox/tree/master/doc/zebr...

It's a simple macro-based typesetting language that can be used to quickly make many different label images from a database. You uploaded the compiled labels into a handheld computer so that labels could be printed on a production line. One option for the computer was the Psion Organizer II.

https://en.wikipedia.org/wiki/Psion_Organiser

mschuster91 4 years ago |

> But in this tarball's filter directory there are only x64 and x86 filters.

For next time you are stuck with that problem: qemu + binfmt_misc can transparently run cross-architecture apps, see https://ownyourbits.com/2018/06/13/transparently-running-bin...

pastudan 4 years ago | |

Thank you! I went down that rabbit hole, but didn't have as detailed of a guide to follow, and quickly gave up. I might still try this so it can show up as a native printer in CUPS.

bauerd 4 years ago |

Similarly, some years ago I prototyped an ESC/POS client (?) for a Bluetooth thermal printer. It was implemented as a Chrome Extension/Chrome App pair, because only Apps were allowed to use Chrome's proprietary Bluetooth API back then. Extension and App communicated via postMessage IIRC. I was shocked how well that hack actually worked. Google then sunset Chrome Apps, and Web Bluetooth never happened.

ctoth 4 years ago | |

Minor quibble, I'm actually using a Bluetooth device via Chrome as I type this message, so I'm pretty sure Web Bluetooth did in fact happen.

plumeria 4 years ago | | |

Interesting, I didn't know about Web Bluetooth. Mobile browsers seem to have the most complete implementations [0].

[0] https://developer.mozilla.org/en-US/docs/Web/API/Web_Bluetoo...

mikece 4 years ago |

The phrase "Just because you can doesn't mean you should" immediately comes to mind.

frankenst1 4 years ago |

Misleading title. "Printer driver" suggests a piece of software which makes the printer accessible for other programs. The software in this article merely converts an image into a different format.

pastudan 4 years ago | |

I suppose you're right... "CUPS Filter" might be a better word than "Driver", but I'm not sure most people would be familiar with that term before reading the full post. It would not be hard to add this script into CUPS as a filter so that it's accessible to all programs. At the end of the day, that's all that a driver is: a filter + a PPD, and the PPD already exists.

Cloudef 4 years ago | |

Lots of printers usually dont need a driver nowadays. They listen to some port where you can input data. Sometimes even simply netcat a pdf.

Here's "driver" i did for star's receipt printer: https://git.cloudef.pw/escpos2raster.git/tree/src/bin/starpb...

davman 4 years ago |

I did something pretty similar for a Brother thermal printer, it took a couple of weeks and I completely lost my mind at one point when I tried to print a single pixel and it ended up as a gigantic block... https://daveirvine.me/#ninety_bytes_is_720_bits

kotaKat 4 years ago |

> But I bought this Polono label printer off Amazon for ~$140, which was a steal compared to the Zebra models that start around $500.

Secret: Go to Alibaba and find suppliers that will sell you a Zebra ZP888 for around ~$125/unit. They're a Chinese-market version of the venerable LP2844, a workhorse in the shipping industry for over two decades now, and they're brand new.

Edit: Also forgot: If you use a service like Shippo (https://goshippo.com/), you can get an API that'll dump ZPL shipping labels out. Chain your warehouse system to Shippo for the label, then chain the ZPL out to the script and out to the printer.

- Make sure the DPI of the document is correct (e.g. 203dpi) - Make sure the document does not need to be scaled (and scaling to fit is disabled) (for 4x6 that means 812 x 1218 pixels max) - Make sure the document is black and white (no grayscale)