racing-overlay

• when build check if app running, if yes, close it before build, and after build, start it again

Racing Pedal Overlay — Development Skill

Project Overview

Single-binary transparent always-on-top HUD for sim racing. Displays a scrolling pedal graph, gear indicator, speed readout, and steering wheel icon. Split into 5 source files under src/.

Target platform: Windows (uses Win32 FFI for AC shared memory + monitor size).
Toolchain: stable-x86_64-pc-windows-msvc (pinned in rust-toolchain.toml).
Build: cargo build --release — binary at target/release/racing_pedal_overlay.exe.

Architecture

Main thread (eframe/egui)          Background thread (std::thread)
┌──────────────────────┐           ┌──────────────────────┐
│ OverlayApp::update() │◄─mpsc────│ spawn_telemetry_thread│
│  input::read_inputs()│          │  read_ac_shared_physics│
│  update_history()    │          │  probe_all_shm()      │
│  poll_telemetry()    │          └──────────────────────┘
│  widgets::draw_*()   │
│  debug::draw_debug() │
└──────────────────────┘

Source File Map

File	Lines	Purpose
src/main.rs	~310	App state, entry point, OverlayApp struct, update_history(), poll_telemetry(), App::update()
src/telemetry.rs	~290	TelemetryData, AC SHM FFI (read_ac_shared_physics()), SHM probe infra, spawn_telemetry_thread()
src/widgets.rs	~230	draw_graph(), draw_gear(), draw_speed(), draw_wheel(), draw_resize_grip() — all free fns
src/input.rs	~95	axis_to_pedal(), axis_to_pedal_inv(), read_inputs() — gilrs + keyboard
src/debug.rs	~190	draw_debug_overlay() — floating debug panel with axis log, SHM probe, toggles. Local-only, gated behind cfg(debug_assertions), excluded from git.

Key Structs & Functions

Item	File	Purpose
TelemetryData	telemetry.rs	Data packet from telemetry thread → UI via mpsc
AcPhysicsSnapshot	telemetry.rs	Fields read from AC shared memory (FFI)
read_ac_shared_physics()	telemetry.rs	Win32 FFI: OpenFileMappingA → reads Local\acevo_pmf_physics
spawn_telemetry_thread()	telemetry.rs	Background thread: 60 Hz SHM poll loop, sends TelemetryData
probe_all_shm()	telemetry.rs	Scans all known SHM names, logs non-zero fields
Sample	main.rs	Single point in pedal history ring buffer
OverlayApp	main.rs	Root app state: hardware inputs, history, telemetry, UI
OverlayApp::new()	main.rs	Constructor: transparent visuals, spawns telemetry thread
read_inputs()	input.rs	Polls gilrs axis events + keyboard fallback
update_history()	main.rs	Records pedal samples at SAMPLE_RATE_HZ (60 Hz)
poll_telemetry()	main.rs	Drains mpsc, updates gear/speed/ABS state, clears stale
draw_graph()	widgets.rs	Scrolling pedal trace with ABS/TC colored segments
draw_gear()	widgets.rs	Gear indicator with RPM color shift
draw_speed()	widgets.rs	Speed readout in km/h
draw_wheel()	widgets.rs	Miniature rotating steering wheel
draw_resize_grip()	widgets.rs	Bottom-right resize with 500ms hover delay
draw_debug_overlay()	debug.rs	Debug panel: axis log, SHM probe, inversion/visibility toggles

Critical Design Patterns

Scaling

All widget sizes, fonts, strokes, and margins are proportional to:

let scale = available_height / 56.0;  // 56 = reference height in px

Never use absolute pixel values for widget internals. Always multiply by scale.

ABS Detection

• AC shared memory (AC Evo 0.6+):
  • SHM name: Local\acevo_pmf_physics (falls back to Local\acpmf_physics)
  • Field at offset 252 (abs_field, f32, 0.0–1.0) — oscillates during ABS intervention
  • Threshold: > 0.01 triggers ABS active; raw float stored as abs_vibration for graph coloring
  • TC field at offset 204 (f32) — > 0.5 triggers TC active
  • abs_source = "shm"

ABS in the Graph

• abs_vibration (f32, 0.0–1.0) is stored per Sample — raw per-tick signal, NOT smoothed
• The abs_held bool (300ms hold timer) exists only for the debug overlay text — NOT used for graph coloring
• Brake line: segment-split by abs_vibration > 0.05 threshold — red (normal) vs orange (ABS active), same line width
• Throttle line: segment-split by tc_active bool — green (normal) vs yellow (TC active), same line width; wide semi-transparent glow behind TC segments
• Segments use bridge points so there are no gaps between color transitions
• No fill-to-zero, no per-sample gradient — these cause barcode/artifact patterns

Telemetry Thread

• Pure std::thread::spawn — no tokio, no async
• Polls read_ac_shared_physics() at ~60 Hz via 16ms sleep loop
• Also runs SHM probe subsystem that scans all known mapping names and diffs against baseline
• Data sent via std::sync::mpsc::channel — UI drains to latest snapshot each frame

AC Shared Memory Layout (acevo_pmf_physics)

All fields packed(4), offsets in bytes:

• 4: gas (f32)
• 8: brake (f32)
• 12: fuel (f32)
• 16: gear (i32) — AC uses 0=R, 1=N, 2=1st, 3=2nd...
• 20: rpms (i32)
• 24: steerAngle (f32)
• 28: speedKmh (f32)
• 204: tc field (f32) — 0.0/1.0 oscillation
• 252: abs field (f32) — 0.0–1.0 vibration intensity
• 364: clutch (f32)

Gear Encoding

AC reports: 0=Reverse, 1=Neutral, 2=1st gear, etc. The telemetry thread subtracts 1 before sending: (snap.gear - 1) as i8 → -1=R, 0=N, 1=1st...

Window Setup

• Borderless, transparent, always-on-top via egui::ViewportBuilder
• Sized to ~26% of monitor width, 5:1 aspect ratio
• Positioned at bottom-center, 4% above screen edge
• Draggable anywhere (entire panel is a drag zone)
• Resize via bottom-right grip (visible after 500ms hover)

Graph Time Window

• Default 8 seconds (DEFAULT_HISTORY_SECONDS)
• User-adjustable via [ / ] keys (2–30 seconds range)
• History buffer trimmed on each update_history() call

Common Modification Scenarios

Adding a new data field from the sim

1. Add field to TelemetryData in telemetry.rs
2. Populate it in spawn_telemetry_thread() — read from AC shared memory at the correct offset
3. Add corresponding field to OverlayApp in main.rs
4. Read it in poll_telemetry() (and clear in the stale-data branch)
5. Display it in widgets.rs or create a new draw_*() function

Adding a new widget

1. Create pub fn draw_widget(ui: &mut Ui, ..., h: f32, w: f32) in widgets.rs
2. Use scale = h / 56.0 for all sizing
3. Allocate space with ui.allocate_exact_size()
4. Paint with ui.painter() — use p.rect(), p.galley(), p.circle_stroke(), etc.
5. Add to the horizontal layout in App::update() in main.rs — account for width in fixed calculation
6. Add visibility toggle in debug.rs (vis_btn())

Changing axis mapping

• The match axis block in input.rs maps gilrs axes to throttle/brake/clutch/steering
• Use debug mode (D) to identify axis codes for different hardware
• axis_to_pedal() = direct (pressed = +1.0), axis_to_pedal_inv() = inverted (pressed = -1.0)

Modifying the scrolling graph

• History buffer: VecDeque<Sample>, capped to history_seconds (default 8s, adjustable 2–30s)
• Sample rate: SAMPLE_RATE_HZ (60 Hz) — controlled in update_history()
• Rendering: egui_plot::Plot with Line segments, X axis = relative time, Y axis = 0–100%
• Brake/throttle segments split by ABS/TC state for color changes — modify the segment-building loops in draw_graph() in widgets.rs

Dependencies & Versions

Crate	Version	Notes
eframe	0.30	egui native backend
egui_plot	0.30	Must match eframe major version
gilrs	0.11	Gamepad/wheel HID input

Gotchas

• AC Evo 0.6+ SHM name change: Mapping renamed from acpmf_physics to acevo_pmf_physics. The code tries the new name first, falls back to old.
• AC Evo integer ABS fields broken: The i32 fields abs_in_action (offset 676) / tc_in_action (offset 672) are always 0 in AC Evo — use the float fields at offsets 252 (abs) and 204 (tc) instead.
• Gear off-by-one: AC uses 0=R, 1=N, 2=1st. Must subtract 1 for correct display.
• gilrs axis variance: Different wheels report on different axes; Moza devices show as RawGameController with Unknown axis types
• Transparent window: clear_color must return [0,0,0,0] and panel_fill must be TRANSPARENT — otherwise rounded corners show opaque background
• No simetry/tokio: These dependencies were removed in v0.3.0. All telemetry is via direct Win32 SHM FFI in a plain std::thread.