QRCode Barrel

A Garmin Connect IQ barrel (library) for generating and rendering QR codes on-device. Pure Monkey C — no network calls, no external services.

• Module: QRCode
• Min API level: 3.2.0
• Version: 1.0.0

Features

• On-device QR generation. Encodes a string to a QR matrix entirely on the watch / Edge device.
• Reed-Solomon error correction. All four levels supported: L (7%), M (15%), Q (25%), H (30%).
• Two encoder variants:
  • Encoder — synchronous, single-call encoding. Best for fast devices.
  • EncoderChunked — splits the work across Timer ticks (50 ms chunks) so slow devices don't trip the Connect IQ watchdog.
• Renderer with bitmap caching. Uses BufferedBitmap (or BufferedBitmapReference on API ≥ 4.0) so the O(n²) module draw only happens when the data, size, or colors change — subsequent frames are a single blit.
• Round-screen aware. Renderer fits the QR inside the inscribed square on round displays and centers it automatically.
• Configurable colors via Renderer.setColors(fg, bg).
• Optional label below the code via Renderer.drawWithLabel(dc, label).
• Wide device coverage. The barrel declares ~130 products — Forerunner, Fenix, Epix, Edge, Venu, Vivoactive, Approach, Descent, Instinct, MARQ, D2, and more (see manifest.xml).

Limitations

• Alphanumeric mode only. Input is uppercased and must consist of 0-9, A-Z, space, or $%*+-./:. No byte mode, no UTF-8, no Kanji. URLs that need lowercase characters won't fit.
• Versions 1–3 only. That's 21×21, 25×25, or 29×29 modules. Capacity caps out at ~84 alphanumeric characters (V3, level L). Longer payloads will not encode.
• Fixed mask pattern. Mask 5 is hard-coded — the encoder does not run the standard penalty-score search to pick the optimal mask. In practice scanners read it fine, but it isn't strictly spec-optimal.
• Quiet zone is 1 module, not the spec-recommended 4, to maximise usable area on small displays. Scanners have been observed to handle this without issue but it is non-standard.
• Consuming apps must restrict their supported device list. The barrel ships with the full device list, but any app depending on it has to narrow <iq:products> in its own manifest.xml to the devices it actually targets (the Connect IQ compiler will not auto-intersect).
• No raw bitmap export. The renderer draws to a Dc; there is no API to extract the matrix as a PNG or external image.
• Colors are caller-controlled. setColors(fg, bg) paints whatever it's given. For scannability you almost always want COLOR_BLACK foreground on COLOR_WHITE background — even on AMOLED hosts where the surrounding activity-screen theme is dark, because scanners require dark-on-light. Matching the host's dark theme will produce an unscannable negative.

Using the barrel

1. Add the dependency

In your app's barrels.jungle:

QRCode = [/path/to/qr-code-barrel/barrel.jungle]
base.barrelPath = $(base.barrelPath);$(QRCode)

In your app's manifest.xml:

<iq:barrels>
    <iq:depends name="QRCode" version="1.0.0"/>
</iq:barrels>

Make sure your app's <iq:products> list is restricted to devices you actually support.

2. Simple (synchronous) usage

Good for newer devices where encoding completes well inside one event loop tick.

using QRCode;

var encoder = new QRCode.Encoder(2, QRCode.Encoder.ERROR_LEVEL_L);
if (encoder.encode("HELLO 123")) {
    var renderer = new QRCode.Renderer(encoder);
    renderer.setColors(Graphics.COLOR_BLACK, Graphics.COLOR_WHITE);
    renderer.calculateLayout(dc);
    renderer.draw(dc);
    // or: renderer.drawWithLabel(dc, "HELLO 123");
}

3. Chunked (asynchronous) usage

Recommended on older / slower devices (e.g. fr245) to avoid watchdog timeouts. The encoder progresses one state per timer tick and invokes your callback when done.

using QRCode;

var chunked = new QRCode.EncoderChunked();
chunked.startEncode(
    "HELLO 123",
    2,                              // version 1-3
    QRCode.Encoder.ERROR_LEVEL_L,
    method(:onEncodeComplete)       // callback
);

function onEncodeComplete(encoder as QRCode.Encoder?) as Void {
    if (encoder != null) {
        mRenderer = new QRCode.Renderer(encoder);
        WatchUi.requestUpdate();
    }
}

See examples/qr-app/ for a complete standalone watch-app that uses the chunked encoder, handles the "Encoding…" loading state, and re-renders on layout changes.

Public API summary

QRCode.Encoder

• new Encoder(version, errorLevel) — version 1–3, ERROR_LEVEL_L|M|Q|H
• encode(data as String) as Boolean — returns false if input isn't alphanumeric or doesn't fit
• getMatrix(), getSize()

QRCode.EncoderChunked

• startEncode(data, version, errorLevel, callback)
• stopEncode(), isEncoding(), isComplete(), getEncoder()

QRCode.Renderer

• new Renderer(encoder)
• setColors(fg, bg) — invalidates the cached bitmap if changed
• calculateLayout(dc) — call before the first draw and whenever screen size changes
• draw(dc), drawWithLabel(dc, label)
• invalidateCache() — call after replacing the QR data

Building

The Makefile at the repo root builds the example app and runs tests:

make build       # build the example data-field
make run         # build + launch in the simulator (PRODUCT=fr255 by default)
make test        # run the unit tests under test/

Override PRODUCT=... to target a different device, e.g. make run PRODUCT=vivoactive5.