Does anyone have experience with external HID touch monitors?

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By LSS4181, Senior Member on 13th May 2020, 07:27 AM
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Recently I got myself a Sculptor 16.1'' external portable monitor that has multi-touch and gravity sensors. The monitor claimed to support many smartphones including ours as well as some others like ROG Phone 1/2. While most other functionalities work (screen outputs at 1920x1080 @ 120Hz, USB-C Power Delivery works), touch and gravity sensors don't work as expected. Haven't tested about audio, but at present I'm not able to redirect audio to the monitor at the moment (the monitor seems to use HDMI for audio).

I'm currently on Havoc 3.5 GSI, with Trinity kernel and MR3 vendor. Can confirm that hid_multitouch is built into the kernel according to the kernel config. However, I couldn't find anything about how to configure the external touch panel and gravity sensor, despite both of them have been properly detected by the system:
1. A CH340 USB-Serial port (1A86:7523) which I believe is the gravity sensor. This device can be picked up by apps like Serial USB Terminal.
2. A Silicon Works SW4101C (29BD:4101) which is most likely the touch panel.

Some information online suggests me to create an IDC for the touch panel's device ID (at present it's identical to that of qwerty2.idc, except I now specified the device is an external device), and some even suggested to patch the kernel's hid-multitouch.c to add the device's ID and information into it, but hid-multitouch.c suggested otherwise, that a default method would be used for unspecified HID devices (that only devices known to have some quirks should be included along with the code for the quirks). I checked the stock ROM's /system/usr/idc and found nothing about external touch panels, either. (If anyone has experiences with such on stock ROM it'd be appreciated)

The gravity sensor is not really working at all (maybe this requires a specialized USB serial app). For the touchscreen part, I could at best get working touches from upper-left part of the screen (about 2/3 of total screen, I think), and only when the phone is in landscape mode (in portrait mode the touchscreen does not function at all). However, it seems sliding works on the entire screen as long as the touch is started from the area that has working touches. Touch is still unstable as some incorrect touches may occasionally occur (probably cable/power related). Also, my phone would generate a tremendous amount of heat when the monitor is attached, and doesn't seem to be able to boot properly if it's been overheated (like about 60-70 celsius).

Not sure if external touch panels are still new, or that such is not really practical for Android smartphones to use (compared to desktops and laptops), the information I could find about this is very limited (that it might require some vendor-specific system modes to function properly, which Huawei and Samsung phones seem to provide). I intend to use this panel as a substitute for my Pixel C which is now showing its age, as it could not handle certain recently released games very well anymore.
21st May 2020, 02:56 PM |#2  
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Thanks Meter: 106
After some research it seems setting the phone's screen size to 1920x1080 will make the touchscreen work on the entire screen, although one may need to set the density as well to keep the size of items the same as before.

wm size 1080x1920
Please note that you'll need to manually revert the resolution later on. The resolution you changed here persists across reboots!

wm size reset
However, the touch panel is still erratic and can cause issues with games where touches may not work as intended (multi-touch does work). Not sure if using a different cable/adapter might help, as similar issues can happen on phone's own screens as well. The use of such monitors may be limited for now as I cannot find any way to enable things like desktop mode, or get the touch panel to work when the phone is in portrait mode.

EDIT: Not sure about the monitor itself, but even with some better cables and adapter the touch panel is still not in a good conditions (either it would stop responding, or it generates unexpected touch signals). A 65W power adapter connection is required to properly function (30W connections is not enough). Guess I'll just use it for other non-Android purposes and get a real tablet (like Galaxy Tab S6) instead...

I did try searching about similar topics regarding external touchscreens on Android. However, the ones I could find were mostly quite old, dated when Android was still at around KitKat or even earlier.

As for audio, I couldn't find anything about it anywhere in the settings. And I only just realized some Type-C cables are rated only at USB 2.0 speed (which is the case for most charging-oriented cables, despite them being rated 65W or even 100W).
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