Optional centered marker origin (setOriginCentered) — webarkit-testing#38

[kalwalt]

Summary

Adds an opt-in option so the tracked pose origin is the marker centre instead of the reference image's top-left corner. With it on, AR content placed at (0,0,0) sits in the middle of the marker.

Implements the library half of webarkit/webarkit-testing#38.

Why opt-in / default OFF

Verified the full ArtoolkitX OCVT chain — it never centres (TrackingPointSelector uses raw top-left pixels; ARTrackable2d only negates Y,Z columns + scales translation; even the example drawCube only lifts +Z). So WebARKit's current corner origin already matches ArtoolkitX. Centring is a WebARKit convenience → default OFF preserves parity and existing behaviour.

How

When enabled, the 3D object points are offset by (_pattern.size.width/2, _pattern.size.height/2) just before solvePnP:

if (_centerOrigin) {
    const float cx = _pattern.size.width * 0.5f, cy = _pattern.size.height * 0.5f;
    for (auto& p : objPoints) { p.x -= cx; p.y -= cy; }
}

Offsetting the object points moves only the solved translation; the rotation is unchanged (orientation unaffected). Applied to the solvePnP 3D points only — the 2D imgPoints and the matching/template/homography paths stay in raw image space.

API

setOriginCentered(bool) threaded through WebARKitTracker (pimpl) and WebARKitManager (default false). The emscripten binding + JS wiring live in the companion webarkit-testing PR.

Testing

Verified against the static + webcam Teblid examples: true → cube/axes centred on the marker, correct orientation; false/default → back to the corner (no behaviour change).

Refs webarkit/webarkit-testing#38

🤖 Generated with Claude Code

[kalwalt]

Companion JS/binding + examples + build PR: webarkit/webarkit-testing#40