AC Gamepad FX

A Custom Shaders Patch Gamepad FX Lua script for Assetto Corsa. Intercepts raw gamepad inputs every physics frame, runs them through a layered correction pipeline, and writes the results back before they reach the physics engine. No game files modified — works in single-player and online.

Primary goal: confident, stable control at high speed and in traffic.

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⚠️ MANDATORY: AC Controls Pre-Flight Checklist

This script will not work correctly unless AC's built-in controls are set to pass-through mode. Do this before driving.

In Content Manager: Settings (gear icon) → Assetto Corsa → Controls tab

1. Input Method → Gamepad
2. Speed Sensitivity → 0%
3. Steering Speed → 100%
4. Steering Gamma → 100%
5. Steering Filter → 0%
6. Steering Deadzone → 0%

Why this matters: This script owns all steering correction. If AC also applies gamma, deadzone, or filter, the effects stack — your gamma curve gets applied twice, your deadzone gets applied twice, and the result is unusable. There is no way for the script to detect or fix this automatically; you must set these manually.

For step-by-step screenshots showing each setting in Content Manager, see INSTALLATION.md.

If steering feels broken after installing, the AC settings are the first thing to check. See Troubleshooting.md.

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What it does

Five corrections applied in order every frame:

1. Deadzone & gamma curve Removes stick drift with a clean rescaled deadzone (no discontinuity at the edge). A configurable gamma exponent compresses center travel for precision at speed while preserving full authority at full deflection.

2. Speed-sensitive steering ratio At low speed, full stick = full lock. Above a configurable speed threshold, the same input produces progressively less lock — down to 35% at highway speed. Transition is a smooth curve, never a hard cutoff.

3. Dynamic steering limit reduction When front tires slide past the optimal grip angle, the available steering range shrinks proportionally. Prevents the instinct to jab the stick past the point where the tires can respond.

4. Self-steer / countersteer force Simulates caster-angle return-to-center. Reads average front wheel slip and applies a corrective force opposing it, plus a damping term proportional to the current steer angle to kill oscillation. Applied after the slip limit — so the correction is never artificially restricted by the driver input clamp.

5. Frame-rate independent smoothing A per-frame exponential lerp on the final output kills single-frame spikes. Blend weight is defined at 60 fps and auto-scales at any frame rate — identical feel at 60 fps or 165 fps.

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Installation

Copy the MyGamepadFX/ folder to:

assettocorsa/extension/lua/joypad-assist/MyGamepadFX/

Activate in Content Manager → Settings → Custom Shaders Patch → Gamepad FX → MyGamepadFX.

Complete step-by-step installation with screenshots: INSTALLATION.md.

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File structure

MyGamepadFX/
├── manifest.ini   — CSP plugin declaration
├── config.lua     — all tunable constants (edit this to tune feel)
├── lib.lua        — math helpers: deadzone, gamma, lerp, expSmooth, speedScale, logOnce
├── assist.lua     — pipeline assembly and CSP entry points
└── debug.lua      — live telemetry overlay (disabled by default)

All tuning is in config.lua. assist.lua contains no raw constants.

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Tuning

Edit MyGamepadFX/config.lua:

DEADZONE          = 0.08   -- stick deadzone radius; find minimum that kills drift
GAMMA             = 1.6    -- >1 compresses center, raises for more precision at speed
STEER_SMOOTH      = 0.12   -- blend weight at 60 fps; raise for more lag, lower for sharper
SPEED_SCALE_START = 60     -- km/h where scaling begins
SPEED_SCALE_END   = 180    -- km/h where scaling reaches minimum
SPEED_SCALE_MIN   = 0.35   -- authority at top speed (0.35 = 35% of full lock)
COUNTERSTEER_GAIN = 0.45   -- self-steer strength; raise until slides self-correct
COUNTERSTEER_DAMP = 0.30   -- must stay >= COUNTERSTEER_GAIN * 0.6 to prevent oscillation
SLIP_LIMIT_START  = 0.15   -- front slip level where limit kicks in
SLIP_LIMIT_RANGE  = 0.25   -- slip range for full reduction
SLIP_LIMIT_MIN    = 0.70   -- minimum authority at peak slip

GAS_DEADZONE      = 0.01   -- removes trigger drift at rest
GAS_GAMMA         = 1.1    -- slight curve for smooth power delivery
BRAKE_DEADZONE    = 0.01   -- avoids unintended light brake from trigger drift
BRAKE_GAMMA       = 1.0    -- linear brake (no curve)

HAPTICS_ENABLED   = false  -- set true if your controller supports trigger rumble

Tuning order: deadzone → gamma → speed scale → countersteer gain → damp → slip limit → smoothing last.

If the car oscillates (tank-slapper), raise COUNTERSTEER_DAMP before touching COUNTERSTEER_GAIN.

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Debug overlay

Enable the live telemetry overlay during tuning by uncommenting two lines in assist.lua:

local dbg = require('debug')   -- line 1: uncomment this

And inside script.update, uncomment the dbg.draw({...}) block. Also set in config.lua:

DEBUG_MODE = true

Shows raw input, post-scale value, steer limit, driver input, self-steer contribution, combined signal, smoothed output, front slip, speed, actual steer angle, and frame time — updated every frame via ac.debug().

Never ship with this enabled.

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Requirements

• Assetto Corsa with Custom Shaders Patch v0.2.0 or later
• A gamepad (tested layout: left stick X = steering, right trigger = throttle, left trigger = brake)

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Troubleshooting

See Troubleshooting.md for a full Q&A covering common symptoms.

Quick reference:

• Steering twitchy/spikey → AC Steering Gamma not at 100%
• Dead zone at center → AC Steering Deadzone not at 0%
• Laggy feel → AC Steering Filter not at 0%
• Car drifts at center → raise DEADZONE in config.lua
• Car oscillates → raise COUNTERSTEER_DAMP in config.lua