# Getting the Gamepad USB Device Name

Unreal exposes `UInputDeviceSubsystem::GetMostRecentlyUsedHardwareDevice()`, which
returns an `FHardwareDeviceIdentifier`. In stock Unreal this is nearly useless: on
Windows it toggles between `"WindowsApplication"` (KBM) and `"XInputController"`
(any XInput pad); on Linux it returns nothing meaningful at all. It cannot
distinguish a DualSense from an Xbox pad.

The USB-reported device name (e.g. `"Sony Interactive Entertainment Wireless
Controller"`) is what we want to surface. This document describes the changes
required on each platform to put that name into `FHardwareDeviceIdentifier`.

## How `FHardwareDeviceIdentifier` Gets Populated

Input drivers wrap their `MessageHandler->OnControllerButton/Analog` calls in an
`FInputDeviceScope` (stack-allocated, thread-local stack of pointers). The scope
carries `InputDeviceName` (driver class) and `HardwareDeviceIdentifier` (physical
device string). When the input event reaches `UInputDeviceSubsystem`, those two
fields are copied into the `FHardwareDeviceIdentifier` record for that user.

So the fix on each platform is the same shape: **at device-connect time, cache
the USB device-name string; in the per-event scope, pass it as the
`HardwareDeviceIdentifier`.**

## Windows: Patch the GameInput Plugin

Location: `Engine/Plugins/Runtime/GameInput/Source/GameInputBase/`.

The Microsoft GameInput SDK already exposes the data we need on every device via
`GameInputDeviceInfo::displayName` (a `wchar_t*`). The plugin reads it for log
lines (`GameInputUtils.cpp:18-23`) but does not propagate it.

Steps:

1. **Cache at connect.** Add `FString CachedDisplayName` to
   `FGameInputDeviceContainer`. In its constructor / device-info init path
   (`GameInputDeviceContainer.cpp:44`, where `Info` is in scope), set:
   ```cpp
   CachedDisplayName = FString(Info->displayName);
   ```
   `TCHAR == wchar_t` on Windows, so the conversion is direct. Lifetime matches
   the container — cleared automatically on disconnect.

2. **Make the container reachable from `FGameInputEventParams`.** The processor
   already gets a `Device` pointer; add a `Container` pointer so
   `GetHardwareDeviceIdentifierName` can read the cached string.

3. **Return it from `GetHardwareDeviceIdentifierName`**
   (`GameInputDeviceProcessor.cpp:61`). After the existing
   `bOverrideHardwareDeviceIdString` block, before the family-bucket switch:
   ```cpp
   if (Params.Container && !Params.Container->CachedDisplayName.IsEmpty())
   {
       return Params.Container->CachedDisplayName;
   }
   ```
   The override path still wins (explicit dev intent); the family-bucket
   fallback handles devices with empty `displayName`.

Total: ~10 lines plus the field. All inside `#if GAME_INPUT_SUPPORT`.

The user must enable the GameInput plugin and disable the default `XInputDevice`
plugin (otherwise both drivers will dispatch events for the same pad).

## Linux: Patch `LinuxApplication.cpp`

Location: `Engine/Source/Runtime/ApplicationCore/Private/Linux/LinuxApplication.cpp`.

SDL already provides the device name via `SDL_GameControllerName()`. The Linux
path calls it once for a log line in `AddGameController` (line 2175) and then
discards it. The Linux path also does not push an `FInputDeviceScope` at all
around its controller events — that's the second half of why
`GetMostRecentlyUsedHardwareDevice` is useless on Linux.

Steps:

1. **Store the name.** Add `FString DeviceName` to `SDLControllerState`. In
   `AddGameController` (~line 2175), assign:
   ```cpp
   ControllerState.DeviceName = UTF8_TO_TCHAR(SDL_GameControllerName(Controller));
   ```

2. **Wrap controller-event dispatch in a scope.** Around the
   `MessageHandler->OnControllerButton*/OnControllerAnalog` block (starting
   ~line 518):
   ```cpp
   FInputDeviceScope Scope(
       nullptr,
       FName("LinuxApplication"),
       ControllerState.DeviceId.GetId(),
       ControllerState.DeviceName);
   // ... existing dispatch ...
   ```
   Use `"LinuxApplication"` for `InputDeviceName` to mirror the Windows
   convention.

Total: ~12 lines. No third-party dependencies, no engine plugins, no per-device
config tables.

## What This Does Not Solve

- **Stock XInput on Windows.** If we keep the default `XInputDevice` plugin,
  events continue to come through `XInputInterface.cpp` with a fixed
  `"XInputController"` identifier. XInput itself does not expose VID/PID or
  device strings. Recovering the name there requires correlating the XInput
  slot with a Raw Input HID via the `IG_xx` token in the Raw Input device path,
  then calling `HidD_GetProductString` — a separate, more involved patch.
  GameInput is the cleaner answer on Windows.

- **XInput-wrapped pads under GameInput.** A DualSense routed through Steam
  Input or DS4Windows will surface as the wrapper's display name (e.g. ViGEm),
  not as the underlying physical device. This is a property of the wrapper, not
  fixable from our side.

- **`displayName` is not a stable identifier.** It is a human-readable name
  whose exact text varies by OS version, driver, and USB descriptor. Use it for
  prompt-set selection and logging. Do not use it as a save-game key.
