Lineariasrr - A Universual DirectInput 8 based Force Feedback (FFB) LUT Wrapper

A lightweight, per-game DirectInput 8 (dinput8.dll) proxy wrapper designed to intercept steering wheel Force Feedback commands, apply a custom Look-Up Table (LUT), and send the linearized output forces to the physical wheel base.

This wrapper is primarily designed to improve force feedback linearity and eliminate motor deadzones on entry-level gear- or belt-driven steering wheels (such as Logitech G25/G27/G29/G920/G923 or Thrustmaster T150/T300) in games that do not natively support LUT files.

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⚠️ Anti-Cheat Warning

Warning

This wrapper DLL (as with all mods in general) is intended for single-player games. Many online multiplayer games with anticheat systems might flag this mod as a cheat vector and result in a ban. Use it at your own risk.

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Installation & Setup

Follow these steps to generate a linearization profile for your specific wheel and install it in your game:

Step 1: Install the Wrapper

1. Download the precompiled dinput8.dll from releases and copy it into your game's main executable folder (where the game's main .exe file is located).

Step 2: Generate Your Custom LUT Profile

By measuring your wheel's specific hardware characteristics and correct them, you can generate a calibration file:

1. Follow this guide to generate a LUT table specifically for your wheel (Skip if you already have an LUT table).
2. Rename the generated file to ffb_lut.txt, and copy it into the game's main executable folder next to dinput8.dll.

Note

The generated file will consist of input-to-output ratios (values between 0.0 and 1.0). If you prefer, you can also write/edit this file manually. Example ffb_lut[ffb_test.cpp](ffb_test.cpp).txt (to compensate for a 5% motor deadzone):

0.0, 0.0
0.02, 0.08   # Maps 2% game force to 8% motor output to clear deadzone
0.05, 0.13   # Maps 5% game force to 13% motor output
0.10, 0.19
0.40, 0.49
1.00, 1.00

Step 3: Configure In-Game Settings

1. Launch the game.
2. Navigate to the game's in-game controller/FFB settings.
3. Set "Min Force" or "Minimum Force" to 0%! Because your custom LUT now fully handles deadzone correction and linear force scaling at the driver level, keeping this setting active in-game will cause force feedback to feel overly harsh or clip.

Step 4: Verify It is Running

Check the dinput8_lut.log file created in your game folder after launch. You should see entries confirming the device wrapper initialized and successfully intercepted FFB updates:

[INIT] Logger started. Log file: ...\dinput8_lut.log
[SYSTEM] Loading real dinput8.dll from: C:\WINDOWS\system32\dinput8.dll
[MAIN] DirectInput8Create called.
[LUT] Successfully loaded LUT with 50 entries.
[DEVICE] Proxy device created. Waiting for FFB calls...
[FFB] SUCCESS: Intercepted first FFB call!

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Features

• Dynamic FFB Interception: Intercepts IDirectInputDevice8W effect parameters (specifically GUID_ConstantForce) at the API level.
• Custom LUT Mappings: Applies linear interpolation based on the local ffb_lut.txt file.
• Lightweight & Thread-Safe: High-performance COM proxy interface with thread-safe execution.
• Diagnostics Tool Included: Includes ffb_test.exe to scan for FFB devices, configure signed axis limits, and apply test forces to verify the LUT behaves correctly without launching a game.

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How It Works

Windows applications load libraries like dinput8.dll by searching the local application directory before looking in system folders (DLL redirection).

By placing this wrapper in the game's executable folder:

1. The game loads our custom dinput8.dll.
2. Our wrapper loads the real system DLL from C:\Windows\System32\dinput8.dll and forwards all standard calls.
3. When the game initializes a force feedback device and creates a Constant Force effect, our wrapper intercepts the COM interfaces (IDirectInputDevice8 and IDirectInputEffect).
4. Whenever the game updates the FFB force magnitude (via SetParameters or CreateEffect), the wrapper intercepts the raw torque value, queries the LUT file, applies the linearization math, and forwards the modified force to the wheel driver.

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Calibration and Testing Tool (ffb_test.exe)

The included console application allows you to test the FFB loop safely without running a full game.

1. Ensure your steering wheel is plugged in, powered, and active.
2. Run ffb_test.exe from a command prompt.
3. The utility will:
   • Load the local wrapper DLL and scan for attached FFB game controllers.
   • Acquire exclusive access and turn off default auto-centering.
   • Apply a centering force.

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Compiling from Source

If you wish to compile the binaries yourself, you will need a C++ compiler (such as GCC/MinGW-w64).

Run the included build.bat script, or compile via command prompt:

# Compile the dinput8.dll wrapper
g++ -O2 -shared -std=c++17 -static -o dinput8.dll main.cpp logger.cpp lut.cpp proxy_device.cpp proxy_dinput.cpp dinput8.def -ldxguid -lkernel32 -luser32 -lole32

# Compile the testing utility
g++ -O2 -std=c++17 -static -o ffb_test.exe ffb_test.cpp -ldinput8 -ldxguid -lkernel32 -luser32

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License

This project is open-source and free to modify or distribute. Use at your own discretion.