Fix arm swing accumulation and add stable bar grip orientation

Author: a-baran-orhan

packages/posecode-render/src/contacts.ts

@@ -205,13 +205,44 @@ export function swingArms(
     HIP_EULER.setFromQuaternion(contraHip.quaternion, "XYZ");
     if (Math.abs(HIP_EULER.x) < 1e-3) continue; // legs still → no swing
     SWING_EULER.setFromQuaternion(shoulder.quaternion, "XYZ");
-    SWING_EULER.x += HIP_EULER.x * SWING_GAIN;
+    // This pass runs every render frame. Assign the procedural channel instead
+    // of adding to last frame's result, otherwise an unauthored shoulder keeps
+    // accumulating rotation (most visibly the left arm in a forward lunge).
+    SWING_EULER.x = HIP_EULER.x * SWING_GAIN;
     shoulder.quaternion.setFromEuler(SWING_EULER);
     changed = true;
   }
   if (changed) m.root.updateMatrixWorld(true);
 }
 
+const GRIP_FRAME = new THREE.Quaternion().setFromAxisAngle(
+  new THREE.Vector3(0, 1, 0),
+  Math.PI,
+);
+
+/**
+ * Give gripping wrists a complete overhand contact frame. Arm IK only
+ * constrains wrist position, leaving hand orientation underdetermined; without
+ * this pass the fingers inherit the forearm direction and can point above the
+ * bar. In root space the palm faces back (-Z), the fingers extend down (-Y),
+ * and the wrist remains exactly on its solved anchor.
+ */
+export function orientBarGrips(m: Mannequin, grips: readonly GripTarget[]): void {
+  let changed = false;
+  for (const g of grips) {
+    const side = /_(left|right)$/.exec(g.effector)?.[1];
+    if (!side) continue;
+    const wrist = m.bones.get(`wrist_${side}`);
+    if (!wrist?.parent) continue;
+    const rootWorld = m.root.getWorldQuaternion(new THREE.Quaternion());
+    const desiredWorld = rootWorld.multiply(GRIP_FRAME);
+    const parentWorld = wrist.parent.getWorldQuaternion(new THREE.Quaternion());
+    wrist.quaternion.copy(parentWorld.invert().multiply(desiredWorld));
+    changed = true;
+  }
+  if (changed) m.root.updateMatrixWorld(true);
+}
+
 /** Max head turn toward a look target (radians) so the neck never over-rotates. */
 export const MAX_LOOK = 55 * (Math.PI / 180);
 const LOOK_FWD = new THREE.Vector3(0, 0, 1);

packages/posecode-render/src/index.ts

@@ -27,7 +27,7 @@ import {
   type ClipSource,
 } from "./clips.js";
 import { depenetrate } from "./depenetrate.js";
-import { alignFloorPalms, levelPlantedFeet, wrapGrip, relaxHands, swingArms, aimHead } from "./contacts.js";
+import { alignFloorPalms, levelPlantedFeet, wrapGrip, relaxHands, swingArms, aimHead, orientBarGrips } from "./contacts.js";
 
 const DEG = Math.PI / 180;
 
@@ -536,7 +536,9 @@ export function createViewer(
       if (joints.length === 0) continue;
       solveCCD({ joints, limits, effector, target }, 12);
     }
-    // 3. Finger wrap.
+    // 3. Resolve the wrist roll left underdetermined by positional arm IK.
+    orientBarGrips(mannequin, grips);
+    // 4. Finger wrap.
     wrapGrip(mannequin, grips);
   }
 

packages/posecode-render/test/contacts.test.ts

@@ -1,7 +1,7 @@
 import { describe, it, expect } from "vitest";
 import * as THREE from "three";
 import { buildMannequin } from "../src/mannequin.js";
-import { levelPlantedFeet, relaxHands, swingArms, aimHead } from "../src/contacts.js";
+import { levelPlantedFeet, relaxHands, swingArms, aimHead, orientBarGrips } from "../src/contacts.js";
 import { groundFigure } from "../src/groundlock.js";
 
 const DEG = Math.PI / 180;
@@ -104,6 +104,43 @@ describe("swingArms (L4.2)", () => {
     swingArms(m, new Set(), new Set(["left"]));
     expect(m.bones.get("shoulder_left")!.rotation.x).toBeCloseTo(before, 5);
   });
+
+  it("is idempotent across render frames instead of accumulating a spin", () => {
+    const m = buildMannequin();
+    m.bones.get("hip_right")!.rotation.x = -0.6;
+    swingArms(m, new Set(), new Set());
+    const once = m.bones.get("shoulder_left")!.quaternion.clone();
+    for (let frame = 0; frame < 120; frame++) swingArms(m, new Set(), new Set());
+    expect(m.bones.get("shoulder_left")!.quaternion.angleTo(once)).toBeLessThan(1e-6);
+  });
+});
+
+describe("orientBarGrips", () => {
+  it("resolves wrist roll without moving a hand off its grip point", () => {
+    const m = buildMannequin();
+    const wrist = m.bones.get("wrist_left")!;
+    wrist.rotation.y = 1.7;
+    m.root.updateMatrixWorld(true);
+    const position = wrist.getWorldPosition(new THREE.Vector3()).clone();
+    orientBarGrips(m, [{ effector: "hand_left", anchor: "bar_left" }]);
+    expect(wrist.getWorldPosition(new THREE.Vector3()).distanceTo(position)).toBeLessThan(1e-6);
+
+    const palm = new THREE.Vector3(0, 0, 1)
+      .applyQuaternion(wrist.getWorldQuaternion(new THREE.Quaternion()));
+    const fingers = new THREE.Vector3(0, -1, 0)
+      .applyQuaternion(wrist.getWorldQuaternion(new THREE.Quaternion()));
+    expect(palm.dot(new THREE.Vector3(0, 0, -1))).toBeGreaterThan(0.999);
+    expect(fingers.dot(new THREE.Vector3(0, -1, 0))).toBeGreaterThan(0.999);
+  });
+
+  it("is stable when applied repeatedly", () => {
+    const m = buildMannequin();
+    const grips = [{ effector: "hand_right", anchor: "bar_right" }];
+    orientBarGrips(m, grips);
+    const once = m.bones.get("wrist_right")!.quaternion.clone();
+    for (let frame = 0; frame < 60; frame++) orientBarGrips(m, grips);
+    expect(m.bones.get("wrist_right")!.quaternion.angleTo(once)).toBeLessThan(1e-6);
+  });
 });
 
 describe("aimHead (L4.3 look-at)", () => {