BarnLights Renderer

This codebase will start and display a rendering engine for the customisable LED lights installed in the Elkenmist barn. It will output formatted RGB data in JSON format at up to 60FPS. The intenstion is for this to be consumed by a UDP sender, and then sent to some microcontroller firmware.

Minimal Node + browser setup that:

• renders gradients / solid / noise onto a 2D virtual scene,
• applies strobe / brightness / tint / pitch/yaw transforms / gamma,
• samples per your layout JSON into per-row "slices",
• emits SLICES_NDJSON to stdout (one line per frame),
• serves a live preview with a light barn perspective and per-LED colored dots.
• allows saving and loading effect presets through the UI with a thumbnail panel of saved presets, storing a preview image with each. Saving with an existing name replaces the previous preset.

Quick start

1. Open your terminal
2. Navigate to this directory
3. Execute the commands (node v20-22 required)

npm install
npm start

4. Go to localhost:8080 in your browser

Running tests

npm test

Output contract

The engine writes one NDJSON object per rendered frame to stdout. Each line represents the color data for all configured sections.

{
  "ts": 1714000000,
  "frame": 0,
  "fps": 60,
  "format": "rgb8",
  "sides": {
    "left": {
      "row_A1": { "length": 180, "rgb_b64": "..." },
      "row_A2": { "length": 120, "rgb_b64": "..." }
    },
    "right": {
      "row_A1": { "length": 200, "rgb_b64": "..." }
    }
  }
}

• ts – UNIX timestamp (seconds) when the frame was generated.
• frame – zero-based frame counter.
• fps – frames-per-second cap applied to the render loop.
• format – color encoding; currently rgb8, meaning each LED is three bytes [R,G,B] with values 0–255.
• sides – object keyed by layout side names such as left and right. Each side contains an object keyed by layout section IDs. For each section:
  • length – number of LEDs in that section.
  • rgb_b64 – base64 string containing length*3 bytes. Decoding yields [R0,G0,B0, R1,G1,B1, ...] following the LED order defined in the layout.

Consumers should read lines individually, parse the JSON, decode rgb_b64 for each section, and map the resulting RGB byte arrays to hardware or downstream systems.

About the code

Architecture

• bin/engine.mjs launches the HTTP server and invokes the engine's start function, streaming NDJSON frames.
• src/render-scene.mjs implements shared scene rendering, post-processing and the renderFrames helper used by both the engine and UI.
• src/engine.mjs runs the render loop with renderFrames and exposes live parameters.
• src/server.mjs exports a startServer helper that serves the UI and relays WebSocket param updates.
• src/ui/ contains the browser preview and controls.

Runtime parameters are grouped under effects for effect-specific settings and post for modifiers like brightness, tint and strobe which can be applied on top. A renderMode parameter controls how scenes map to the two walls: duplicate renders once for both, extended renders a double-width scene and splits it, and mirror flips the scene horizontally for the right wall. Both the engine and browser preview rely on renderFrames to handle these modes.

Frame pipeline

1. renderFrames draws the active effect, applies post-processing and fills the leftFrame and rightFrame buffers based on renderMode.
2. Each frame is sliced according to the configured layouts and emitted as base64-encoded rgb8 NDJSON.
3. The browser preview reuses these frame buffers to draw the scene and per-LED indicators.

Acknowledgements

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