Integrate U8g2 library

[soburi]

This PR integrates the u8g2 library into Zephyr.

---

Origin

Name of project hosting the original open source code

U8g2: Library for monochrome displays, version 2

Purpose

Brief description of what this software does

U8g2 is a monochrome graphics library for embedded devices. U8g2 supports monochrome OLEDs and LCDs

Mode of integration

Describe whether you'd like to integrate this external component in the main tree
or as a module, and why. If the mode of integration is a module, suggest a
repository name for the module

As External Module.

Maintainership

List the person(s) that will be maintaining the integration of this external code
for the foreseeable future. Please use GitHub IDs to identify them. You can
choose to identify a single maintainer only or add collaborators as well

@soburi

Pull Request

#61533 (this PR)

Description

Long description that will help reviewers discuss suitability of the
component to solve the problem at hand (there may be a better options
available.)

U8g2 is a graphics library for monochrome displays.
It can draw graphics primitives(lines, circles, etc.)
It has a font renderer and bundles various fonts.
U8g2 also contains LCD driver functions, which is needless in Zephyr.
The feature completely drops when any code does not reference it.

What is its primary functionality (e.g., SQLLite is a lightweight
database)?

Graphics drawing for monochrome display.

What problem are you trying to solve? (e.g., a state store is
required to maintain ...)

To enhance graphic drawing capability for monochrome display.

Why is this the right component to solve it (e.g., SQLite is small,
easy to use, and has a very liberal license.)

LVGL is unsuitable for monochrome display, and CFB optimizes for text rendering.

Dependencies

What other components does this package depend on?

No dependencies.

Revision

Version or SHA you would like to integrate initially

7851fd39858551dfa9c4af4a597e0ad85a180807
(https://github.com/soburi/u8g2 contains modification for zephyr)

License

Please use an SPDX identifier (https://spdx.org/licenses/), such as
BSD-3-Clause

BSD-2-Clause

And contains various license font data. (see below)

---

I think most issues are already discussed in #38755 and solved.

• It is a significant gap in functions between the CFB and the LVGL. The U8g2 is suitable to fill the gap.
• U8g2 is one of the few available libraries specialized to handle monochrome display, which I think is valuable to integrate.
• U8g2 has the function of driving LCD devices. But no need to use it in Zephyr. We use it just as a graphics library.
• U8g2 is a simple graphics library when not using its own LCD driver code. It has no dependency on other libraries. (From a portability perspective, it is a "pure C language" library.)
• U8G2 handles 'VTILED' pixel format. It is the native format of monochrome display, and it is also the Zephyr display driver format.
  It means no overhead to convert pixel format between Zephyr and u8g2.
• Additionally, introducing the U8G2 makes it able to draw graphics on a monochrome display, so I think CFB can optimize for implementations with stricter resource constraints. It is good to select CFB/U8G2/LVGL by resource constraint.

Mostly part of u8g2 licensed under BSD-2.
But bundled fonts are not so.
I removed files that were released under incompatible licenses with Zephyr.

I append the scancode result.

scancode -clpeu --classify --summary --verbose --html u8g2.html u8g2

And rechecked by hand, the result is https://github.com/soburi/u8g2/blob/zephyr/README.zephyr.md.

[zephyrbot]

The following west manifest projects have been modified in this Pull Request:

Name	Old Revision	New Revision	Diff
u8g2	N/A	soburi/u8g2@7851fd3 (zephyr)	N/A

Note: This message is automatically posted and updated by the Manifest GitHub Action.

[nordicjm]

@jfischer-no wasn't this module requested before and declined for being too similar to in-tree modules?

[soburi]

@nordicjm @jfischer-no

@jfischer-no wasn't this module requested before and declined for being too similar to in-tree modules?

From this discussion,

#58366 (comment)

I'm considering to remove the off-screen buffer function from cfb and use it differently with u8g2 and resource limits.
(Considering whether u8g2 can be used for applications that use off-screen buffers. Such as graphical drawing.)
I will consider whether to submit it formally, but I made it a draft because it seemed to work well for the time being.

#38755

As far as past discussions are concerned, there are some points of contention, but they are not necessarily negative.

[dolence]

I am very glad to see there is an effort to bring u8g2 support to Zephyr. How could I test it? Os that possible? The lack of support to a small footprint (and yet very capable) library to be used with more constrained devices is the reason I don't use Zephyr on my projects.

[soburi]

I am very glad to see there is an effort to bring u8g2 support to Zephyr. How could I test it? Os that possible? The lack of support to a small footprint (and yet very capable) library to be used with more constrained devices is the reason I don't use Zephyr on my projects.

It should work with board that equips monochrome display. Such as reel board.
Otherwise, you need to write little configuration for connecting monochrome display.

[jfischer-no]

I see no reason to add this library with many licensing issues when similar functionality is already implemented (by you) in CFB.

[nashif]

TSC: under review, we are considering to introduce an area for integration optional modules which will allow listing this as something a user can integrate in their application without making it a module maintained in the default manifest.

[soburi]

TSC: under review, we are considering to introduce an area for integration optional modules which will allow listing this as something a user can integrate in their application without making it a module maintained in the default manifest.

I can't touch the details of discussion, but I strongly welcome to add the method to introducing module by weak integration.

[dolence]

I see no reason to add this library with many licensing issues when similar functionality is already implemented (by you) in CFB.

Isn't CFB character only? This isn't the same as CFB. I think CFB is similar to u8x8. U8g2 would be great. Following this.

I've some pictures attached of u8g2 in action on a project. UI with menus are supported trough MUI.

[dolence]

I'm moving my project from STM23CubeIDE to Zephyr. How can I test this as an external out of the tree module?

[soburi]

#61505 was merged,
I changed this PR to use submanifests/optional.yaml.

[nashif]

this should be done as an external module, i.e. by providing a reference and enabled by those who need it in their manifest, see https://docs.zephyrproject.org/latest/develop/manifest/index.html#external-projects-modules