feat: Implement fix for sunlight fading issue

[allgoewer]

Summary

• What is the goal of this PR?

The goal of this PR is to deliver a fix for or at least mitigate the impact of the issue described in #561

• What changes are included?

This PR includes a new option "Sunlight Fading Fix" under "Settings -> Display".

When set to ON, we will disable the displays analog supply voltage after every update and turn it back on before the next update.

Additional Context

• Until now, I was only able to do limited testing because of limited sunlight at my location, but the fix seems to be working. I'll also attach a pre-built binary based on 0.16.0 (current master) with the fix applied to the linked ticket, as building this fix is a bit annoying because the submodule open-x4-sdk also needs an update.
• PR in open-x4-sdk needs to be merged first, we also need to add another commit to this here PR, updating this dependency.
• I decided to hide this behind a default-OFF option. While I'm not really concerned that this fix might potentially damage the display, someone more knowledgeable on E-Ink technology could maybe have a look at this.
• There's a binary attached in the linked issue, if someone has the required sunlight to test this in-depth.

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AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing, please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? NO

[allgoewer]

I still got no feedback from anyone regarding the effectiveness of this PR. I was able to do only limited testing due to weather conditions but it seemed to do the trick.

[osteotek]

as discussed in #561 (comment) seems to be working.

[cbix]

Nice fix, I got the black version anyway but would this theoretically save battery as well?

[allgoewer]

In theory, yes. But I didn't measure.

[insunaa]

doesn't actually seem to work for me :( but setting the refresh interval to every page-turn keeps the text readable enough

[allgoewer]

@insunaa Would you mind providing a short clip?

Are you sure there is no difference between enabled / disabled fix?
With the fix disabled, you should see the screen completely fading to white over the period of a minute or so, with the fix enabled the fading should stop as soon as the screen-update finishes.
There will still be fading during the screen update, even with the fix enabled. That is expected.

[pablohc]

doesn't actually seem to work for me :( but setting the refresh interval to every page-turn keeps the text readable enough

Are you sure it's because of the sun? I perceive degradation of the screen, and I always have the two X4s (black and white) in my room without any exposure to the sun. Somebody has made a post in reddit comparing 0.16 vs 1.1.0 and the old version of the firmware showed more contrast in the black screen than in the newer FW.

[insunaa]

@pablohc some people on reddit speculated it was caused by infrared light heating the ink particles and changing their magnetism for a short bit

@allgoewer I'll make a video as soon as there's sunlight in my area again. For me the fading isn't just the dark pixels turning light, it's also the light pixels splotchily turning dark and after-images of the last ~5-10 refreshes appearing. this happens much more strongly if I am actively flipping pages, but it also happens to the book cover when the device is in deep sleep (as in: put it to sleep while not affected by sunlight and then several minutes later exposing it to direct sunlight)

it also doesn't seem to be affected by UV-A (365nm), I have a UV-A flashlight and neither shining it at the e-ink screen nor shining it between the buttons or into the USB-C port causes any noticeable changes to the display content (regardless of whether the fix is enabled or not)

[allgoewer]

Yeah, that sounds like a completely different issue.
Nonetheless, really wanna see the vid :-)