Re-aim teleport arc from grip toward the target ray's indicated point

On Apple Vision Pro the target ray originates at the head, so launching
the arc from the grip position with the raw target ray direction offset
the trajectory by the hand-to-head parallax - the landing depended on
where the hand happened to be when the pinch registered.

The aim ray now launches from the grip but points at the spot the
target ray indicates (its navigation-plane intersection, or a far point
along the ray), making the landing independent of the initial hand
registration. For tracked-pointer controllers the grip and ray origin
coincide, so this reduces exactly to the unmodified target ray.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: willeastcott

scripts/esm/xr-navigation.mjs

@@ -24,6 +24,8 @@ const tmpSegDir = new Vec3();
 const tmpToCam = new Vec3();
 const tmpSide = new Vec3();
 const tmpAimOrigin = new Vec3();
+const tmpAimDir = new Vec3();
+const tmpAimPoint = new Vec3();
 
 const arcVertexGLSL = /* glsl */ `
     attribute vec3 vertex_position;
@@ -565,20 +567,41 @@ class XrNavigation extends Script {
     }
 
     /**
-     * Returns the world-space point the aim visualization should start from. The target ray
-     * origin sits at the head for gaze/pinch-style input (e.g. Apple Vision Pro transient
-     * pointers), so prefer the handheld grip position when the input source has one.
+     * Computes the world-space aim ray for an input source, writing it into tmpAimOrigin and
+     * tmpAimDir. The arc launches from the handheld grip position when the input source has
+     * one, because the target ray origin sits at the head for gaze/pinch-style input (e.g.
+     * Apple Vision Pro transient pointers). The direction is then re-aimed from the grip
+     * toward the point the target ray indicates - using the raw target ray direction from the
+     * hand would offset the trajectory by the hand-to-head parallax, making the landing depend
+     * on where the hand happened to be when the pinch registered. For tracked-pointer
+     * controllers the grip and ray origin coincide, so this reduces to the target ray itself.
      *
      * @param {XrInputSource} inputSource - The aiming input source.
-     * @returns {Vec3} The world-space start point.
      * @private
      */
-    _getAimOrigin(inputSource) {
-        // Copy immediately: getPosition() and getOrigin() return references to the input
-        // source's internal vectors, which the engine reuses as scratch space on the next
-        // getDirection()/getOrigin() call
+    _getAimRay(inputSource) {
+        // Copy immediately: getOrigin()/getDirection()/getPosition() return references to the
+        // input source's internal vectors, which the engine reuses as scratch space on
+        // subsequent calls
+        tmpAimDir.copy(inputSource.getDirection());
+        tmpAimOrigin.copy(inputSource.getOrigin());
+
         const grip = inputSource.grip ? inputSource.getPosition() : null;
-        return tmpAimOrigin.copy(grip || inputSource.getOrigin());
+        if (!grip) return;
+
+        // Aim point: where the target ray meets the navigation plane, or a far point along
+        // the ray when it never descends to it
+        let t = this.maxTeleportDistance;
+        if (tmpAimDir.y < -0.001) {
+            const tPlane = (tmpAimOrigin.y - this.groundHeight) / -tmpAimDir.y;
+            if (tPlane > 0 && tPlane < this.maxTeleportDistance * 2) {
+                t = tPlane;
+            }
+        }
+        tmpAimPoint.copy(tmpAimDir).mulScalar(t).add(tmpAimOrigin);
+
+        tmpAimOrigin.copy(grip);
+        tmpAimDir.sub2(tmpAimPoint, tmpAimOrigin).normalize();
     }
 
     /**
@@ -646,7 +669,8 @@ class XrNavigation extends Script {
         if (!rec) {
             rec = { point: new Vec3(), valid: false };
             this._arcHits.set(inputSource, rec);
-            this._computeArcHit(this._getAimOrigin(inputSource), inputSource.getDirection(), rec);
+            this._getAimRay(inputSource);
+            this._computeArcHit(tmpAimOrigin, tmpAimDir, rec);
         }
         if (!rec.valid) return;
 
@@ -840,7 +864,8 @@ class XrNavigation extends Script {
                 rec = { point: new Vec3(), valid: false };
                 this._arcHits.set(inputSource, rec);
             }
-            this._computeArcHit(this._getAimOrigin(inputSource), inputSource.getDirection(), rec);
+            this._getAimRay(inputSource);
+            this._computeArcHit(tmpAimOrigin, tmpAimDir, rec);
 
             const visual = this._getArcVisual(inputSource);
             visual.entity.enabled = true;