420p label offset

[Mousketeer]

The labels are printed offset to the bottom (when reading the text) of the label.

Attached is a photo of the result (tested with release v2.2.1 on Linux):

• a 12mm tape (black on white), with four prints in increasing tape-width specification.
• a 6mm tape (black on yellow) with the same four prints.
  My 19mm tape ran out before I could test and is on order now, but I suspect that aligns correctly.

A possibility could be that the position of the tape is wrongly referenced:

• The cartridges all sit in the cartridge-holder, with the cartridge edge facing the top of the text being the fixed reference surface for the cartridge. This is the unlabeled face of the cartridge, with the labeled side facing the door of the printspace.
• However, the 6mm and 12mm (and presumably 9mm) cartridges are the same height.
  -- The 6mm tape sits centered in the oversized housing, with spacers above and below.
  -- The 12mm tape takes up the whole height of the cartridge.
  -- The printhead thus sticks out on the side of the cartridge with the label.
• The 19mm tape housing is higher, but again starts from this top reference surface.

Also attached is a schematic (apologies to your eyes)

(I lack any skill in printer driver development...)

[tomek-szczesny]

It is very strange because it uses the same cartridge models as PnP (D1), so I assume they used the same printing header. Why would it work differently?
Have you cross checked with official software or .. well, official method of use?

However, if this is shown to be a consistent behavior on this model of label printers then I guess it could be a matter of adding an offset for this particular model.

[Mousketeer]

The unit has a little on-device keyboard and that works fine, the mode-switch-to-storage-enclosed "dymo mini" (or something like that) windows software also prints perfectly aligned. The official windows app from their site didn't see my labelprinter.
I looked at youtube video's of the PnP with D1 cartridges, and they look to be printing in the same orientation - so I'm at an utter loss.

How would I go about experimenting with offsets? I don't have the first clue about driver development.

[khrise]

I can confirm the behavior for my 420p. Using the official windows app, it prints correctly. Using dymoprint under arch linux, I have the same offsets as described by @Mousketeer .
I'd be happy to help or try things out. But, same over here: It would be great to get some (even rough) directions where to start.
@tomek-szczesny , can you help here?

[tomek-szczesny]

@khrise I'm afraid we know pretty much the same about this code, as I'm not a contributor. Just someone who likes their PnP and tests new features. :)
But fear not, this is not a driver per se, just a program that creates USB packets and sends them.
I think that a portion of the code that differentiates between various models of Dymo printers must be found, and add a line that overrides offset value if it exists. If not, such value must be added.

My understanding of Python is very limited, I can read it mostly but not contribute, unfortunately.

[Mousketeer]

As luck would have it my new 19mm tape came in this week, here are some tests:
A QR, large (5000px) jpg, and text at size 19 (dymoprint -t 19 -qr "contents" -p image.jpg) on 19mm tape. The top of the lowercase letters is just about in the centre of the tape.

And, again on 19mm tape, text with the different sizes (-t NN).

How the 12mm tape (green) is seated in the machine compared to the 19mm:

And this is also interesting (coincidence?):

So various clues:

• The 19mm tape print is not centered, but too far to the bottom (side of cartridge with identification label)
• The print offset is in the wrong direction

As for the material properties of the tapes:

• The 19 and 12mm tapes are aligned at the top of the cartridge
• The top of the 6mm tape sits at approx 3mm from the top of the cartridge.
• 9mm still unknown

An older version of the full windows software suite works perfectly.

Any hints on where to start digging would be greatly appreciated :-)

[tomek-szczesny]

Excellent work! If you're able to calculate necessary offsets for each tape size, that would be half job done. :)
The code suggests the print resolution is 8 dots per mm, and offsets must be added in dots, not mm.

D1 series cartridges (that fits PnP for example) appear to be centered regardless of tape size, which confirms your findings. Here's a photo of 9mm and 12mm I have.

So clearly a table must be added, with offsets per each printer model and tape size. I suggest doing it in such a way that if a printer is not present in table, 0 offset is assumed, for maximum compatibility.

I think this is the place to start:
https://github.com/computerlyrik/dymoprint/blob/2476b1722b0fbede7720be0d554e591c672fc54d/src/dymoprint/dymo_print_engines.py#L395C34-L395C34

Here, label_matrix is created, which I assume contains raw print data.
Then, dymo_devs is created and populated, which contains a list of connected printers. At some point one printer is chosen, and by reading this variable we may figure out which printer is in use.

Now, just before the printing is about to begin, here:

dymoprint/src/dymoprint/dymo_print_engines.py

Line 508 in 2476b17

print("Printing label..")

the label_matrix can be manipulated to implement offset.

I'm not familiar with good Python practices, but knowing other projects, a table with offsets per each printer and tape width should be stored in a separate constants file. For example here:
https://github.com/computerlyrik/dymoprint/blob/master/src/dymoprint/constants.py

I can offer a check whether your changes did not break the PnP compatibility. :)

[tomek-szczesny]

Now when I think about it, this will not solve the problem, sorry. Like I said, I can only speculate because I don't know anything more than any of you.

label_matrix contains only the data to be printed, so it is only as wide as the selected tape size. The actual USB data sending happens in this file:
https://github.com/computerlyrik/dymoprint/blob/master/src/dymoprint/labeler.py#L205
If someone completely understands this file, I guess the problem will be solved quickly.
I speculate that it's the PnP printer itself that centers received data in the printing area. If print rows are shorter than maximum, the printer may choose to print on its header center, which made sense in older models (I suppose D1 was the first tape cassette type they had).
Looking at four test prints on 19mm tape I see that 420p behaves differently, aligning the print area to the bottom. This has to be compensated for, because the code assumes automatic centering.

I fear that in order to print on your printers correctly, the printer must always think the tape is 19mm wide, and label_matrix have extra blank rows (or columns) to move the print area properly.

[khrise]

Mmh, ok, I'm getting somewhere. If I change the y-part of the position to 0 here:
https://vscode.dev/github/computerlyrik/dymoprint/blob/master/src/dymoprint/dymo_print_engines.py#L299
I get the following result. The position of the text appears to be correct, but the upper part of the text is cropped.

(Printing on 9mm tape)

[maresb]

If you run dymoprint --preview, does what you see on the screen correspond at all to what's being printed?

[maresb]

If dymoprint --preview appears correct, then probably the issue is how the data is being encoded and sent to the printer. It could be that whatever scheme works for encoding up to 12mm breaks down at 19mm and requires some adjustment.

[khrise]

Good point - tried the preview at the very moment. And nope: the preview is also "broken" in a similar way.

So the positioning appears to be correct, but the image does not contain the whole text.

[tomek-szczesny]

The vscode links don't work on my desktop, just saying.

Yup, that's exactly why I later said my first comment isn't the best idea.
I think what should be done is to add more columns to label_matrix, to match (19 * 8) matrix width, and make this call:
https://github.com/computerlyrik/dymoprint/blob/2476b1722b0fbede7720be0d554e591c672fc54d/src/dymoprint/dymo_print_engines.py#L506C1-L506C79
always with 19mm tape width.

The trick is to add correct amount of blank columns on front and back of existing matrix for each tape size.

[maresb]

It seems like it works for me. Could the cutoff be a result of the adjustment you made?

$ dymoprint --version
dymoprint 2.2.1
$ dymoprint --preview -t 19 test
Demo mode: showing label..
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[khrise]

Yes, definitly. Using the code from the repo, I get the same (correct) preview. However, I changed the y-offset in dymo_print_engines.py#L299 to 0, just to find out where I can adjust the erroneous offset in the printed labels (the original issue). With this change, the text on the label gets printed as shown above. And also the preview shows that the image already contains only half of the text. So, the image doesn't get rendered correctly, now we have to find how to fix that, in order to implement "switches" for the 420p.
I assume it's either somewhere in render_engine.render_text or render_engine.merge_render