fix: eliminate figure sway and foot skating; realistic grounded mechanics

packages/posecode-eval/src/probe.ts

@@ -68,6 +68,16 @@ export function probeMovement(source: string): ProbeResult {
   const baseRootPos = m.root.position.clone();
   const baseRootQuat = m.root.quaternion.clone();
 
+  // Mirror Viewer.captureGroundTargets(): the grounded base-pose effector
+  // positions are the anchors horizontal foot planting holds feet to.
+  const groundTargets = new Map<string, THREE.Vector3>();
+  for (const ids of Object.values(m.effectors)) {
+    for (const id of ids) {
+      const node = m.bones.get(id);
+      if (node) groundTargets.set(id, node.getWorldPosition(new THREE.Vector3()));
+    }
+  }
+
   // Sample the end of each phase, applying the viewer's per-frame root
   // pipeline: base root → yaw/travel → ground-lock → floor safety clamp.
   const yawQ = new THREE.Quaternion();
@@ -82,7 +92,19 @@ export function probeMovement(source: string): ProbeResult {
     m.root.position.x += info.rootOffset.x;
     m.root.position.z += info.rootOffset.z;
     m.root.updateMatrixWorld(true);
-    applyGroundLock(m, info.groundLock);
+    // Mirror the viewer's per-frame anchors: captured targets carried along
+    // by this phase's yaw/travel so planting composes with choreography.
+    const anchors = new Map<string, THREE.Vector3>();
+    for (const [id, captured] of groundTargets) {
+      const v = captured.clone();
+      if (info.rootYaw !== 0) {
+        v.sub(baseRootPos).applyAxisAngle(WORLD_Y, info.rootYaw).add(baseRootPos);
+      }
+      v.x += info.rootOffset.x;
+      v.z += info.rootOffset.z;
+      anchors.set(id, v);
+    }
+    applyGroundLock(m, info.groundLock, anchors);
     // Viewer safety net: never leave the lowest mesh point below the floor.
     m.root.updateMatrixWorld(true);
     const box = new THREE.Box3().setFromObject(m.root);

packages/posecode-render/src/groundlock.ts

@@ -15,6 +15,14 @@
  * - **Feet only (squat / hinge / roll-down):** drop the body vertically so the
  *   feet stay planted while the legs keep their authored FK bend: the pelvis
  *   lowers. Legs are never CCD-solved (that would overwrite the pose).
+ *   With `anchors`, grounded feet are also held HORIZONTALLY: FK leg motion
+ *   (hip/knee) displaces the feet relative to the root, and without the
+ *   correction the feet skate across the floor while the pelvis stays put —
+ *   backwards from real movement, where planted feet stay fixed and the
+ *   pelvis travels (a squat sits the hips back, a hinge shifts them behind
+ *   the heels). Only feet near the floor anchor (a swing leg in a curl or
+ *   march must stay free), and only the average delta is corrected so
+ *   symmetric spreads (jumping jacks) don't fight the lock.
  *
  * Both paths ground the visible MESH (bounding boxes), not just bone origins:
  * an ankle bone sits ~0.04m above the sole, so anchoring bones alone left the
@@ -71,8 +79,19 @@ function rotateRootAboutPivot(m: Mannequin, pivot: THREE.Vector3, angle: number)
   m.root.updateMatrixWorld(true);
 }
 
-/** Apply ground-lock for the phase's active effector groups (see module doc). */
-export function applyGroundLock(m: Mannequin, active: string[]): void {
+/** A foot whose mesh bottom is within this height counts as planted. */
+const PLANTED_MAX_Y = 0.05;
+
+/**
+ * Apply ground-lock for the phase's active effector groups (see module doc).
+ * `anchors` (optional) maps effector bone ids to the world position each
+ * planted foot should hold, already transformed by the phase's yaw/travel.
+ */
+export function applyGroundLock(
+  m: Mannequin,
+  active: string[],
+  anchors?: ReadonlyMap<string, THREE.Vector3>,
+): void {
   if (active.length === 0) return;
   const ids = activeEffectorIds(m, active);
   const hands = ids.filter((id) => id.startsWith("wrist"));
@@ -120,5 +139,38 @@ export function applyGroundLock(m: Mannequin, active: string[]): void {
       m.root.position.y -= minY;
       m.root.updateMatrixWorld(true);
     }
+    if (anchors) plantFeetHorizontally(m, feet, anchors);
+  }
+}
+
+/**
+ * Translate the root in X/Z so grounded feet return to their anchors (see
+ * module doc). Runs after vertical grounding so "near the floor" is judged in
+ * the final vertical placement.
+ */
+function plantFeetHorizontally(
+  m: Mannequin,
+  feet: string[],
+  anchors: ReadonlyMap<string, THREE.Vector3>,
+): void {
+  const p = new THREE.Vector3();
+  let dx = 0;
+  let dz = 0;
+  let n = 0;
+  for (const id of feet) {
+    const anchor = anchors.get(id);
+    const node = m.bones.get(id);
+    if (!anchor || !node) continue;
+    const box = new THREE.Box3().setFromObject(node);
+    if (!Number.isFinite(box.min.y) || box.min.y > PLANTED_MAX_Y) continue; // swing foot
+    node.getWorldPosition(p);
+    dx += anchor.x - p.x;
+    dz += anchor.z - p.z;
+    n++;
+  }
+  if (n > 0) {
+    m.root.position.x += dx / n;
+    m.root.position.z += dz / n;
+    m.root.updateMatrixWorld(true);
   }
 }

packages/posecode-render/src/index.ts

@@ -145,30 +145,31 @@ export function createViewer(
   scene.add(mannequin.root);
 
   // --- Life layer: breathing + blinking so the figure reads as alive even
-  // when the movement is paused. Breathing is a tiny additive sagittal
-  // rotation layered onto the sampled pose each frame; it can never drift
-  // because timeline.sample() rewrites those quaternions every frame.
+  // when the movement is paused. Both are MESH-only effects. Breathing must
+  // never rotate skeleton bones: an earlier version breathed via tiny
+  // chest/spine rotations, but those ran before ground-lock/pin solving,
+  // which translated the whole figure to re-plant the displaced hands/feet,
+  // so every movement visibly swayed and the head bobbed. Swelling the
+  // ribcage mesh cannot disturb any joint, so authored poses stay exact.
   const BREATH_PERIOD = 3.8; // seconds per breath cycle
   const BLINK_DURATION = 0.13;
-  const LIFE_AXIS = new THREE.Vector3(1, 0, 0);
-  const LIFE_Q = new THREE.Quaternion();
   const eyes = ["eye_left", "eye_right"]
     .map((n) => mannequin.root.getObjectByName(n))
     .filter((o): o is THREE.Object3D => Boolean(o));
+  const ribcage = mannequin.root.getObjectByName("ribcage");
+  const ribcageRestScale = ribcage ? ribcage.scale.clone() : null;
   let nextBlink = performance.now() / 1000 + 2;
 
-  function breatheBone(boneId: string, angle: number): void {
-    const bone = mannequin.bones.get(boneId);
-    if (!bone) return;
-    LIFE_Q.setFromAxisAngle(LIFE_AXIS, angle);
-    bone.quaternion.multiply(LIFE_Q);
-  }
-
   function applyLife(nowSec: number): void {
-    const breath = Math.sin((nowSec * Math.PI * 2) / BREATH_PERIOD);
-    breatheBone("chest", breath * 0.022);
-    breatheBone("spine", breath * 0.012);
-    breatheBone("neck", breath * -0.014); // counter-rotate: head stays level
+    if (ribcage && ribcageRestScale) {
+      // 0..1 inhale fraction; the chest swells mostly front-to-back.
+      const breath = 0.5 + 0.5 * Math.sin((nowSec * Math.PI * 2) / BREATH_PERIOD);
+      ribcage.scale.set(
+        ribcageRestScale.x * (1 + breath * 0.015),
+        ribcageRestScale.y * (1 + breath * 0.01),
+        ribcageRestScale.z * (1 + breath * 0.05),
+      );
+    }
     if (nowSec >= nextBlink + BLINK_DURATION) {
       nextBlink = nowSec + 2.5 + Math.random() * 3;
     }
@@ -224,6 +225,7 @@ export function createViewer(
     // "Ground-lock" means HOLD the effector where the grounded base pose placed
     // it, not drag it to y=0. groundFigure() already set the floor contact.
     groundTargets = new Map();
+    frameAnchorMap.clear(); // drop anchors for effectors no longer captured
     for (const ids of Object.values(mannequin.effectors)) {
       for (const id of ids) {
         const node = mannequin.bones.get(id);
@@ -236,6 +238,30 @@ export function createViewer(
   const WORLD_Y = new THREE.Vector3(0, 1, 0);
   const YAW_Q = new THREE.Quaternion();
 
+  // Per-frame ground anchors: the captured load-time effector positions,
+  // carried along by the phase's yaw/travel so horizontal foot planting
+  // composes with choreography instead of fighting it. Values are mutated in
+  // place each frame; the map is rebuilt on load (captureGroundTargets).
+  const frameAnchorMap = new Map<string, THREE.Vector3>();
+  function frameAnchors(rootYaw: number, rootOffset: { x: number; z: number }): Map<string, THREE.Vector3> {
+    for (const [id, captured] of groundTargets) {
+      let v = frameAnchorMap.get(id);
+      if (!v) {
+        v = new THREE.Vector3();
+        frameAnchorMap.set(id, v);
+      }
+      v.copy(captured);
+      if (rootYaw !== 0) {
+        // Yaw spins the body about the vertical axis through the root, so the
+        // anchors must pivot with it (a quarter-turn carries the feet around).
+        v.sub(baseRootPos).applyAxisAngle(WORLD_Y, rootYaw).add(baseRootPos);
+      }
+      v.x += rootOffset.x;
+      v.z += rootOffset.z;
+    }
+    return frameAnchorMap;
+  }
+
   // Friendly DSL effector aliases → the distal bone whose world position is
   // driven to the reach target.
   const EFFECTOR_BONE: Record<string, string> = {
@@ -406,7 +432,7 @@ export function createViewer(
       mannequin.root.position.x += info.rootOffset.x;
       mannequin.root.position.z += info.rootOffset.z;
       mannequin.root.updateMatrixWorld(true);
-      applyGroundLockTo(mannequin, info.groundLock);
+      applyGroundLockTo(mannequin, info.groundLock, frameAnchors(info.rootYaw, info.rootOffset));
       applyPins(info.pins);
       // Safety net: nothing above ever intentionally pushes part of the body
       // below the floor, so clamp the root up whenever the lowest point dips

packages/posecode-render/src/mannequin.ts

@@ -256,8 +256,11 @@ function addEllipsoid(
 function addTorso(bones: Map<string, THREE.Object3D>, mats: FigureMaterials): void {
   // Hips: wide, slightly flattened, dressed in shorts.
   addEllipsoid(bones.get("pelvis")!, 0.09, [1.4, 1.0, 1.05], [0, -0.02, 0], mats.shorts);
-  // Ribcage: broad across the shoulders, shallow front-to-back.
-  addEllipsoid(bones.get("chest")!, 0.1, [1.5, 1.22, 0.82], [0, 0.03, 0], mats.top);
+  // Ribcage: broad across the shoulders, shallow front-to-back. Named so the
+  // viewer's life layer can swell it for breathing (a mesh-only effect that
+  // can never disturb the skeleton or the solved pose).
+  const ribcage = addEllipsoid(bones.get("chest")!, 0.1, [1.5, 1.22, 0.82], [0, 0.03, 0], mats.top);
+  ribcage.name = "ribcage";
   // Deltoids round off the shoulder line.
   addEllipsoid(bones.get("shoulder_left")!, 0.057, [1.02, 1.12, 1.02], [-0.006, -0.012, 0], mats.top);
   addEllipsoid(bones.get("shoulder_right")!, 0.057, [1.02, 1.12, 1.02], [0.006, -0.012, 0], mats.top);

playground/src/main.ts

@@ -507,7 +507,10 @@ void import("./editor.js").then(({ createPosecodeEditor }) => {
 
 // Renderer: keep Three.js off the critical path, mirroring the landing page.
 void import("posecode-render").then(({ createViewer }) => {
-  viewer = createViewer(canvas);
+  // No idle camera orbit in the playground: the point here is judging the
+  // movement itself, and a permanently rotating scene reads as the figure
+  // swaying. The landing-page hero keeps its showcase orbit.
+  viewer = createViewer(canvas, { autoRotate: false });
   // Exposed for capture/e2e tooling (frame capture drives README GIFs).
   (window as unknown as Record<string, unknown>).__posecodeViewer = viewer;
   wireViewer(viewer);