Sometimes Characters instead of Image is printed

[BigJk]

This behaviour is sometimes encountered on mac while using cups. Printing characters instead of a image might indicate that the printer didn't correctly receive the raster image command and is trying to print the image bytes as characters. It needs to be investigated when this happens and if it's a problem with cups, the printer or S&D itself.

[nbadal]

Might be related to buffer size - at least in the case of my printer (Citizen CT-S310) images taller than 384x2400 or so fail consistently.

One idea floated was to split renders, though we'd need to make sure there aren't margins between images

[BigJk]

Buffer size is definitely one error source depending on printer and yes, we should check if we can print splitted images without margins 😄

Sadly that wouldn't explain the problem I encounter at the moment

On a M1 Macbook:

• First CUPS print works
• Every print after that fails with gibberish even if the image is just 10 pixel height
• Only turning printer on / off before each print works -> Corrupted / print buffer not cleared after CUPS print?
• Writing directly to the virtual USB COM of the printer via libusb everything works normally. No gibberish.

@frshbeetz confirmed that this doesn't happen on his Intel + Mac Setup. Both using CUPS 2.3.4. I will try to dig out some other USB printer I have and check if the same problem happens with CUPS.

[BigJk]

I dug out my old Zjiang ZJ-5890K which was the first printer I used for the project and only has 58mm. I can print even a 1 meter long template without any gibberish. Consecutive cups prints also don't corrupt the printing.

Then I retried some more with the Zjiang ZJ-8330. After fully unplugging until all power is gone, then setting Force Standard Mode to on and Explicit Initialization to off cups decided to start working again. No more gibberish. Seems like it's very picky about these settings with CUPS 🤔

[BigJk]

@nbadal I changed the printing so that chunked prints work. I verified with my printer that no margins were present. You can set it up in the settings.

• Split Height: Height in pixel of each chunk
• Split Delay: Delay in ms after each chunk print. This might be useful for direct usb printing were we don't want to overflow the buffer with too much data in a short time. For cups this can probably stay at 0 as cups itself will be a bit slower with sending prints.

Would be awesome if you could try and see if this fixes the print issue with your printer.

[BigJk]

Thanks to github making the m1 runner available to open source S&D now comes with libusb releases for arm (m1,mX) builds. This should make it possible to avoid the weird behavior of CUPS on arm based macs. I will close this issue for now.