I built a C library to inject multitouch into Android over USB — no root, no ADB, no app

#android #c #opensource

Background

I'm 14, and I wanted to automate touch input on Android from a PC
with as little latency as possible — mainly for game automation
and key mapping.

After researching, I found that AOA (Android Open Accessory)
HID-only mode was the right approach. It's much lower latency
than adb input tap because it bypasses the ADB stack entirely
and sends raw HID reports directly over USB.

I found existing projects for mouse and keyboard HID over AOA,
but nothing for touch panels. So I first built a small program
that reads touch events from a CSV and replays them via AOA HID.
Once that worked, I realized the transport layer could be useful
for a lot of other things, so I extracted it into a library.

What it does

libaoa_hid registers a virtual HID digitizer on Android over
a plain USB cable and streams raw touch reports to it.

No root
No ADB
No companion app on the Android side
Up to 16 simultaneous touch points
Works on Linux, macOS, and Windows (MinGW-w64)
Requires Android 4.1+

The library is a pure transport pipe — no retry logic, no sleep
calls. Timing and error handling are left entirely to the caller.

How it works

AOA 2.0 allows a USB host to register a HID device on Android
without any app on the Android side. The tricky part was getting
the HID descriptor right for a multitouch digitizer — Android
has specific requirements around contact count reporting and
hybrid mode that aren't well documented.

Quick example

AoaDevice *dev = aoa_hid_connect(1600, 2560, 10);
sleep_ms(500); // wait for Android to register the HID device

HidReport r;
memset(&r, 0, sizeof(r));
r.report_id                 = 1;
r.finger[0].tip_inrange_pad = AOA_FINGER_DOWN;
r.finger[0].contact_id      = 0;
r.finger[0].x               = 400;
r.finger[0].y               = 800;
r.contact_count             = 1;
aoa_hid_send_report(dev, &r);

aoa_hid_disconnect(dev);

Use cases

Game automation and key mapping
UI test automation
Robotics / embedded setups that need to drive an Android display

Coming soon

I'm currently working on a companion tool that records tap events
via ADB, converts them to CSV, and replays them through
libaoa_hid — so you can record any interaction and reproduce it
exactly. Will be released when it's ready.