Label Printing Updates

06 Dec 2023 Oliver

Available in the upcoming 0.13.0 stable release are some significant enhancements for label printing functionality. The label printing code has received a major overhaul to allow greater flexibility for label printing plugins, and enabling new features which were not previously possible.

Label Printing Plugins

Previously, we had separate concepts for “native label printing” and “printing via plugins”, with different software pipelines for each. This meant that:

We had a lot of duplicated or inefficient code
External printing plugins did not have the same available features

In #5251 we refactored the label printing codebase entirely, and now all label printing is handled via plugins. A builtin plugin is provided which simply renders a single label as a .pdf file (maintaining previous behavior).

The refactor also provided a number of significant improvements and new functionality:

Background Printing

Printing plugins can run in the foreground - and return a .pdf object - or in the background. Background printing plugins return a response immediately (to prevent blocking of the web application) and the printing is offloaded to the background worker process. This allows flexibility to (for example) communicate with an external physical printing device.

Multiple Labels

Before this refactor, plugins received each label individually, with a single “print job” being sent to the printing plugin for each selected label. This was inefficient, and also meant that the printing plugin did not have the flexibility to handle simultaneous printing of multiple labels.

Now, printing plugins have access to the print_labels method, which receives all labels to be printed. If desired, multiple labels could be printed together onto a single paper sheet (an example of this is below).

The default implementation of print_labels simply calls the existing print_label method in sequence for each separate label - maintaining backwards compatibility for existing plugins.

Printing Options

In PR #5786 we introduced the concept of “printing options”. Each printing plugin can provide a set of printing options which are presented to the user before initiating label printing. This allows for greater flexibility for label printing plugins.

For example, these run-time options could be used to:

Select paper size
Switch between multiple connected printers
Specify the number of copies of each label to print
etc

Label Sheets

In PR #5883, a builtin plugin was developed to print multiple labels to a single “sheet”. This could be used to print a set of labels onto a specialized label sheet with peelable labels, or just a sheet of paper where the individual labels can be cut from the sheet.

This plugin also provides an example of how the printing options can be used to customize printing behavior at runtime.

Example

The images below demonstrate how the new label sheet plugin works.

Select Items to Print

Select a number of individual stock items, for which labels will be printed:

Select Items

Label Printing Dialog

Select the InvenTree Sheet Label Printer plugin:

Select printer

Print Labels

Labels are printed in a regular grid on the resulting sheet. Note that the first three cells have been skipped, as per the selected option in the printing dialog:

Print labels

Available Soon

The new label printing features will be available in the upcoming 0.13.0 stable release. Or, available now in the master code branch!