feat(physics): phase 16 - ludic.physics over Jolt Physics v5.6.0

Our own shim (native/shim/jph_shim.cpp) over Jolt built from the pinned tag with cross-platform
determinism and no fp contraction: shapes as handles (box, sphere, capsule, cylinder, dome,
offset, heightfield, mesh), still/kinematic/dynamic bodies by id with real removal, rays,
top_at and push (what CharacterGround asks), overlaps, buoyancy against the PhysWater port,
contacts recorded in C and drained as PHYS_HIT / PHYS_SPLASH facts. Fixed 1/60 steps, at most four
a frame. Nine tests against the real library, including a pile run twice to the bit.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.physics/native/build.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+# builds lib/<target>/ for ludic.physics: Jolt Physics at a pinned tag, and the shim over it.
+# Cross-platform determinism is on (the Mac and the PC must agree in co-op), and floating point
+# contraction off, which it needs. Objects go to build/native; about a minute on eight cores.
+set -eu
+PKG="$(cd "$(dirname "$0")/.." && pwd)"
+. "$PKG/../../tools/native/lib.sh"
+JOLT_TAG=v5.6.0
+JOLT_SHA=6e069ee0172478cc78182047aac87e5310ba14a67a53348ae14cc37801fd3f8e
+SRC="$PKG/build/src/jolt-$JOLT_TAG"
+native_fetch "$SRC" "https://github.com/jrouwe/JoltPhysics/archive/refs/tags/$JOLT_TAG.tar.gz" "$JOLT_SHA"
+
+OBJ="$PKG/build/native/$(native_target)"
+mkdir -p "$OBJ"
+CXX="$(native_cxx)"
+DEFS="-DNDEBUG -DJPH_CROSS_PLATFORM_DETERMINISTIC -DJPH_OBJECT_LAYER_BITS=16"
+FLAGS="$(native_cflags) -std=c++17 -ffp-contract=off -fno-exceptions -fno-rtti $DEFS -I$SRC"
+case "$(native_target)" in windows-*) FLAGS="$FLAGS -D_CRT_SECURE_NO_WARNINGS" ;; esac
+JOBS="$(getconf _NPROCESSORS_ONLN 2>/dev/null || echo 4)"
+
+# one object per Jolt source, named by its path so two files called the same do not collide
+( cd "$SRC" && find Jolt -name '*.cpp' ) | while read -r f; do
+  o="$OBJ/$(echo "$f" | tr '/' '_' | sed 's/\.cpp$/.o/')"
+  [ "$o" -nt "$SRC/$f" ] || echo "$f $o"
+done | xargs -P "$JOBS" -n 2 sh -c '"$0" '"$FLAGS"' -c "'"$SRC"'/$1" -o "$2"' "$CXX"
+"$CXX" $FLAGS -I"$PKG/native/shim" -c "$PKG/native/shim/jph_shim.cpp" -o "$OBJ/jph_shim.o"
+
+native_link "$PKG" ludicjolt "$OBJ"/*.o

packages/ludic.physics/native/shim/jph_bodies.inl

@@ -0,0 +1,64 @@
+// jph_bodies.inl - bodies by id: added, removed, moved, pushed, read back
+
+// motion 0 still, 1 kinematic, 2 dynamic; layer 0 ground, 1 static, 2 moving; mass 0 = from shape
+JPH_SHIM int jph_body_add(void *w, void *shape, float x, float y, float z, float yaw, int motion, int layer,
+                          float mass, float friction, float bounce) {
+  World *ww = static_cast<World *>(w);
+  EMotionType mt = motion == 2 ? EMotionType::Dynamic : (motion == 1 ? EMotionType::Kinematic : EMotionType::Static);
+  BodyCreationSettings st(static_cast<Shape *>(shape), RVec3(x, y, z), yaw_q(yaw), mt, ObjectLayer(layer));
+  st.mFriction = friction;
+  st.mRestitution = bounce;
+  if (mt == EMotionType::Dynamic && mass > 0.0f) {
+    st.mOverrideMassProperties = EOverrideMassProperties::CalculateInertia;
+    st.mMassPropertiesOverride.mMass = mass;
+  }
+  EActivation act = mt == EMotionType::Static ? EActivation::DontActivate : EActivation::Activate;
+  BodyID id = ww->sys.GetBodyInterface().CreateAndAddBody(st, act);
+  if (id.IsInvalid()) return -1;
+  return int(id.GetIndexAndSequenceNumber());
+}
+
+JPH_SHIM void jph_body_remove(void *w, int id) {
+  BodyInterface &bi = static_cast<World *>(w)->sys.GetBodyInterface();
+  bi.RemoveBody(bid(id));
+  bi.DestroyBody(bid(id));
+}
+
+// position, rotation (x, y, z, w) and velocity into out[10]
+JPH_SHIM int jph_body_read(void *w, int id, float *out) {
+  BodyInterface &bi = static_cast<World *>(w)->sys.GetBodyInterface();
+  if (!bi.IsAdded(bid(id))) return -1;
+  RVec3 p; Quat q;
+  bi.GetPositionAndRotation(bid(id), p, q);
+  Vec3 v = bi.GetLinearVelocity(bid(id));
+  float vals[10] = { float(p.GetX()), float(p.GetY()), float(p.GetZ()), q.GetX(), q.GetY(), q.GetZ(), q.GetW(),
+                     v.GetX(), v.GetY(), v.GetZ() };
+  for (int i = 0; i < 10; i++) out[i] = vals[i];
+  return 0;
+}
+
+JPH_SHIM void jph_body_place(void *w, int id, float x, float y, float z, float yaw) {
+  static_cast<World *>(w)->sys.GetBodyInterface().SetPositionAndRotation(bid(id), RVec3(x, y, z), yaw_q(yaw), EActivation::Activate);
+}
+JPH_SHIM void jph_body_impulse(void *w, int id, float x, float y, float z) {
+  static_cast<World *>(w)->sys.GetBodyInterface().AddImpulse(bid(id), Vec3(x, y, z));
+}
+JPH_SHIM void jph_body_velocity(void *w, int id, float x, float y, float z) {
+  static_cast<World *>(w)->sys.GetBodyInterface().SetLinearVelocity(bid(id), Vec3(x, y, z));
+}
+// a kinematic body driven to where it should be after dt, pushing what it meets
+JPH_SHIM void jph_body_target(void *w, int id, float x, float y, float z, float yaw, float dt) {
+  static_cast<World *>(w)->sys.GetBodyInterface().MoveKinematic(bid(id), RVec3(x, y, z), yaw_q(yaw), dt);
+}
+JPH_SHIM int jph_body_awake(void *w, int id) { return static_cast<World *>(w)->sys.GetBodyInterface().IsActive(bid(id)) ? 1 : 0; }
+
+// water under a body: the surface's height and normal, how buoyant, the drags and the current
+JPH_SHIM int jph_body_buoyancy(void *w, int id, float sy, float nx, float ny, float nz, float buoy, float lin, float ang,
+                               float cx, float cz, float dt) {
+  World *ww = static_cast<World *>(w);
+  BodyInterface &bi = ww->sys.GetBodyInterface();
+  RVec3 p = bi.GetPosition(bid(id));
+  bool in = bi.ApplyBuoyancyImpulse(bid(id), RVec3(p.GetX(), sy, p.GetZ()), Vec3(nx, ny, nz), buoy, lin, ang,
+                                     Vec3(cx, 0.0f, cz), ww->sys.GetGravity(), dt);
+  return in ? 1 : 0;
+}

packages/ludic.physics/native/shim/jph_queries.inl

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+// jph_queries.inl - what is there: a ray, the top a body could step onto, overlaps, a push out
+
+// a ray from o along d (its length the reach) against the layers in mask; the body id or -1, and
+// out[7] the fraction, the point and the normal
+JPH_SHIM int jph_ray(void *w, float ox, float oy, float oz, float dx, float dy, float dz, int mask, float *out) {
+  World *ww = static_cast<World *>(w);
+  RRayCast ray{ RVec3(ox, oy, oz), Vec3(dx, dy, dz) };
+  RayCastResult hit;
+  MaskFilter f(mask);
+  if (!ww->sys.GetNarrowPhaseQuery().CastRay(ray, hit, {}, f)) return -1;
+  RVec3 p = ray.GetPointOnRay(hit.mFraction);
+  Vec3 n = Vec3::sAxisY();
+  BodyLockRead lock(ww->sys.GetBodyLockInterface(), hit.mBodyID);
+  if (lock.Succeeded()) n = lock.GetBody().GetWorldSpaceSurfaceNormal(hit.mSubShapeID2, p);
+  float vals[7] = { hit.mFraction, float(p.GetX()), float(p.GetY()), float(p.GetZ()), n.GetX(), n.GetY(), n.GetZ() };
+  for (int i = 0; i < 7; i++) out[i] = vals[i];
+  return int(hit.mBodyID.GetIndexAndSequenceNumber());
+}
+
+// a ball of radius r let down from (x, from_y, z) at most `depth`: the height of what it lands
+// on, or -FLT_MAX when it lands on nothing in mask
+JPH_SHIM float jph_top_at(void *w, float x, float z, float r, float from_y, float depth, int mask) {
+  World *ww = static_cast<World *>(w);
+  SphereShape ball(r);
+  ball.SetEmbedded();
+  RShapeCast cast = RShapeCast::sFromWorldTransform(&ball, Vec3::sOne(), RMat44::sTranslation(RVec3(x, from_y, z)),
+                                                    Vec3(0.0f, -depth, 0.0f));
+  ClosestHitCollisionCollector<CastShapeCollector> hit;
+  MaskFilter f(mask);
+  ww->sys.GetNarrowPhaseQuery().CastShape(cast, ShapeCastSettings(), RVec3::sZero(), hit, {}, f);
+  if (!hit.HadHit()) return -FLT_MAX;
+  return float(hit.mHit.mContactPointOn2.GetY());
+}
+
+// the bodies (in mask) a ball at (x, y, z) touches, up to cap into ids; returns how many
+JPH_SHIM int jph_overlap(void *w, float x, float y, float z, float r, int mask, int *ids, int cap) {
+  World *ww = static_cast<World *>(w);
+  SphereShape ball(r);
+  ball.SetEmbedded();
+  AllHitCollisionCollector<CollideShapeCollector> hits;
+  MaskFilter f(mask);
+  ww->sys.GetNarrowPhaseQuery().CollideShape(&ball, Vec3::sOne(), RMat44::sTranslation(RVec3(x, y, z)),
+                                             CollideShapeSettings(), RVec3::sZero(), hits, {}, f);
+  hits.Sort();
+  int n = 0;
+  for (const CollideShapeResult &h : hits.mHits) {
+    int id = int(h.mBodyID2.GetIndexAndSequenceNumber());
+    bool seen = false;
+    for (int i = 0; i < n; i++) seen = seen || ids[i] == id;
+    if (!seen && n < cap) ids[n++] = id;
+  }
+  return n;
+}
+
+// an upright body r wide, from y0 to y1, at (x, z): how far to move it in x and z to stand clear
+// of what it overlaps in mask, into out[2]; returns how many things it overlapped
+JPH_SHIM int jph_push(void *w, float x, float z, float r, float y0, float y1, int mask, float *out) {
+  World *ww = static_cast<World *>(w);
+  float half = (y1 - y0) * 0.5f;
+  CylinderShape body(half, r, 0.0f);
+  body.SetEmbedded();
+  AllHitCollisionCollector<CollideShapeCollector> hits;
+  MaskFilter f(mask);
+  CollideShapeSettings cs;
+  cs.mBackFaceMode = EBackFaceMode::CollideWithBackFaces;
+  ww->sys.GetNarrowPhaseQuery().CollideShape(&body, Vec3::sOne(), RMat44::sTranslation(RVec3(x, y0 + half, z)),
+                                             cs, RVec3::sZero(), hits, {}, f);
+  hits.Sort();
+  float px = 0.0f, pz = 0.0f;
+  for (const CollideShapeResult &h : hits.mHits) {
+    Vec3 a = h.mPenetrationAxis;
+    Vec3 flat(a.GetX(), 0.0f, a.GetZ());
+    if (flat.LengthSq() < 1.0e-8f) continue;
+    flat = flat.Normalized() * h.mPenetrationDepth;
+    px -= flat.GetX();
+    pz -= flat.GetZ();
+  }
+  out[0] = px;
+  out[1] = pz;
+  return int(hits.mHits.size());
+}

packages/ludic.physics/native/shim/jph_shapes.inl

@@ -0,0 +1,42 @@
+// jph_shapes.inl - shapes, each a handle the package keeps and frees; null when Jolt refused it
+
+JPH_SHIM void *jph_shape_box(float hx, float hy, float hz) {
+  return keep(BoxShapeSettings(Vec3(hx, hy, hz), 0.02f).Create());
+}
+JPH_SHIM void *jph_shape_sphere(float r) { return keep(SphereShapeSettings(r).Create()); }
+JPH_SHIM void *jph_shape_capsule(float half_h, float r) { return keep(CapsuleShapeSettings(half_h, r).Create()); }
+JPH_SHIM void *jph_shape_cylinder(float half_h, float r) {
+  float cr = r < 0.05f ? r * 0.5f : 0.02f;
+  return keep(CylinderShapeSettings(half_h, r, cr).Create());
+}
+
+// a dome r across and h tall standing on y = 0: the cap of a sphere whose centre is below
+JPH_SHIM void *jph_shape_dome(float r, float h) {
+  float big = (r * r + h * h) / (2.0f * h);
+  RefConst<Shape> s = SphereShapeSettings(big).Create().Get();
+  return keep(RotatedTranslatedShapeSettings(Vec3(0.0f, h - big, 0.0f), Quat::sIdentity(), s).Create());
+}
+
+// a shape moved and turned about y, inside its body
+JPH_SHIM void *jph_shape_offset(void *s, float x, float y, float z, float yaw) {
+  return keep(RotatedTranslatedShapeSettings(Vec3(x, y, z), yaw_q(yaw), static_cast<Shape *>(s)).Create());
+}
+
+// n x n heights (row z, column x) at ox, oz, cell metres apart; FLT_MAX is a hole
+JPH_SHIM void *jph_shape_heightfield(const float *h, int n, float ox, float oz, float cell) {
+  HeightFieldShapeSettings st(h, Vec3(ox, 0.0f, oz), Vec3(cell, 1.0f, cell), uint32(n));
+  return keep(st.Create());
+}
+
+// a triangle mesh for a dock or a cabin: nv vertices (x, y, z) and nt triangles (i, j, k)
+JPH_SHIM void *jph_shape_mesh(const float *v, int nv, const int *tri, int nt) {
+  VertexList vs;
+  vs.reserve(nv);
+  for (int i = 0; i < nv; i++) vs.push_back(Float3(v[i * 3], v[i * 3 + 1], v[i * 3 + 2]));
+  IndexedTriangleList ts;
+  ts.reserve(nt);
+  for (int i = 0; i < nt; i++) ts.push_back(IndexedTriangle(tri[i * 3], tri[i * 3 + 1], tri[i * 3 + 2]));
+  return keep(MeshShapeSettings(vs, ts).Create());
+}
+
+JPH_SHIM void jph_shape_free(void *s) { if (s) static_cast<Shape *>(s)->Release(); }

packages/ludic.physics/native/shim/jph_shim.cpp

@@ -0,0 +1,126 @@
+// jph_shim.cpp - ludic.physics' door into Jolt Physics (phase 16). It keeps the shim rules of
+// packages/README.md: int, long, float and opaque handles cross; no struct by value, no callback
+// into Ludic - contacts are recorded during the step and drained after it; errors are return
+// codes. Jolt's job threads stay in here.
+#include <Jolt/Jolt.h>
+#include <Jolt/RegisterTypes.h>
+#include <Jolt/Core/Factory.h>
+#include <Jolt/Core/TempAllocator.h>
+#include <Jolt/Core/JobSystemThreadPool.h>
+#include <Jolt/Physics/PhysicsSettings.h>
+#include <Jolt/Physics/PhysicsSystem.h>
+#include <Jolt/Physics/Collision/Shape/BoxShape.h>
+#include <Jolt/Physics/Collision/Shape/SphereShape.h>
+#include <Jolt/Physics/Collision/Shape/CapsuleShape.h>
+#include <Jolt/Physics/Collision/Shape/CylinderShape.h>
+#include <Jolt/Physics/Collision/Shape/HeightFieldShape.h>
+#include <Jolt/Physics/Collision/Shape/MeshShape.h>
+#include <Jolt/Physics/Collision/Shape/RotatedTranslatedShape.h>
+#include <Jolt/Physics/Collision/RayCast.h>
+#include <Jolt/Physics/Collision/CastResult.h>
+#include <Jolt/Physics/Collision/ShapeCast.h>
+#include <Jolt/Physics/Collision/CollideShape.h>
+#include <Jolt/Physics/Collision/CollisionCollectorImpl.h>
+#include <Jolt/Physics/Body/BodyCreationSettings.h>
+#include <mutex>
+#include <thread>
+#include <cfloat>
+
+#if defined(_WIN32)
+#define JPH_SHIM extern "C" __declspec(dllexport)
+#else
+#define JPH_SHIM extern "C" __attribute__((visibility("default")))
+#endif
+
+using namespace JPH;
+
+// ---- layers: the ground, the still things on it, and what moves --------------------------
+namespace {
+const ObjectLayer L_GROUND = 0, L_STATIC = 1, L_MOVING = 2, L_COUNT = 3;
+const BroadPhaseLayer BP_STILL(0), BP_MOVING(1);
+
+class BPLayers final : public BroadPhaseLayerInterface {
+public:
+  uint GetNumBroadPhaseLayers() const override { return 2; }
+  BroadPhaseLayer GetBroadPhaseLayer(ObjectLayer l) const override { return l == L_MOVING ? BP_MOVING : BP_STILL; }
+#if defined(JPH_EXTERNAL_PROFILE) || defined(JPH_PROFILE_ENABLED)
+  const char *GetBroadPhaseLayerName(BroadPhaseLayer l) const override { return l == BP_MOVING ? "moving" : "still"; }
+#endif
+};
+class ObjVsBP final : public ObjectVsBroadPhaseLayerFilter {
+public:
+  bool ShouldCollide(ObjectLayer l, BroadPhaseLayer bp) const override { return l == L_MOVING || bp == BP_MOVING; }
+};
+class ObjPairs final : public ObjectLayerPairFilter {
+public:
+  bool ShouldCollide(ObjectLayer a, ObjectLayer b) const override { return a == L_MOVING || b == L_MOVING; }
+};
+// a query's layers as a bit mask (1 ground, 2 static, 4 moving)
+class MaskFilter final : public ObjectLayerFilter {
+public:
+  explicit MaskFilter(int m) : mask(m) {}
+  bool ShouldCollide(ObjectLayer l) const override { return (mask >> l) & 1; }
+  int mask;
+};
+
+// ---- contacts: recorded on Jolt's threads, drained on the game's -------------------------
+const int C_CAP = 512;
+struct Contact { uint32 a, b; float x, y, z, speed; };
+
+class Contacts final : public ContactListener {
+public:
+  void OnContactAdded(const Body &b1, const Body &b2, const ContactManifold &m, ContactSettings &) override {
+    Vec3 n = m.mWorldSpaceNormal;
+    float speed = (b2.GetLinearVelocity() - b1.GetLinearVelocity()).Dot(n);
+    RVec3 p = m.GetWorldSpaceContactPointOn1(0);
+    std::lock_guard<std::mutex> g(lock);
+    if (count >= C_CAP) { lost++; return; }
+    items[count++] = { b1.GetID().GetIndexAndSequenceNumber(), b2.GetID().GetIndexAndSequenceNumber(),
+                       float(p.GetX()), float(p.GetY()), float(p.GetZ()), std::abs(speed) };
+  }
+  std::mutex lock;
+  Contact items[C_CAP];
+  int count = 0;
+  int lost = 0;
+};
+
+struct World {
+  World(int max_bodies, int threads)
+      : temp(16 * 1024 * 1024), jobs(cMaxPhysicsJobs, cMaxPhysicsBarriers, threads) {
+    sys.Init(max_bodies, 0, max_bodies, max_bodies * 4, bpl, ovb, olp);
+    sys.SetContactListener(&contacts);
+  }
+  TempAllocatorImpl temp;
+  JobSystemThreadPool jobs;
+  BPLayers bpl;
+  ObjVsBP ovb;
+  ObjPairs olp;
+  PhysicsSystem sys;
+  Contacts contacts;
+};
+
+bool g_ready = false;
+BodyID bid(int id) { return BodyID(uint32(id)); }
+Quat yaw_q(float yaw) { return Quat::sRotation(Vec3::sAxisY(), yaw); }
+void *keep(const ShapeSettings::ShapeResult &r) {
+  if (r.HasError()) return nullptr;
+  Shape *s = const_cast<Shape *>(r.Get().GetPtr());
+  s->AddRef();
+  return s;
+}
+} // namespace
+
+// Jolt's allocator, factory and types, once per process; 0 when ready
+JPH_SHIM int jph_init(void) {
+  if (g_ready) return 0;
+  RegisterDefaultAllocator();
+  Factory::sInstance = new Factory();
+  RegisterTypes();
+  g_ready = true;
+  return 0;
+}
+
+#include "jph_world.inl"
+#include "jph_shapes.inl"
+#include "jph_bodies.inl"
+#include "jph_queries.inl"

packages/ludic.physics/native/shim/jph_world.inl

@@ -0,0 +1,49 @@
+// jph_world.inl - a physics world: made, stepped, emptied of its contacts, freed
+
+// a world for up to max_bodies; threads 0 means the machine's cores less one, at most four
+JPH_SHIM void *jph_world_new(int max_bodies, int threads) {
+  if (jph_init() != 0) return nullptr;
+  if (threads <= 0) {
+    int hw = int(std::thread::hardware_concurrency()) - 1;
+    threads = hw < 1 ? 1 : (hw > 4 ? 4 : hw);
+  }
+  World *w = new World(max_bodies, threads);
+  w->sys.SetGravity(Vec3(0.0f, -9.81f, 0.0f));
+  return w;
+}
+
+JPH_SHIM void jph_world_free(void *w) { delete static_cast<World *>(w); }
+
+JPH_SHIM void jph_world_gravity(void *w, float y) { static_cast<World *>(w)->sys.SetGravity(Vec3(0.0f, y, 0.0f)); }
+
+// one step of dt seconds in `sub` collision steps; 0 when Jolt reports nothing wrong
+JPH_SHIM int jph_world_step(void *w, float dt, int sub) {
+  World *ww = static_cast<World *>(w);
+  EPhysicsUpdateError e = ww->sys.Update(dt, sub < 1 ? 1 : sub, &ww->temp, &ww->jobs);
+  return e == EPhysicsUpdateError::None ? 0 : -int(e);
+}
+
+// after adding many still bodies at once, before the first query
+JPH_SHIM void jph_world_optimize(void *w) { static_cast<World *>(w)->sys.OptimizeBroadPhase(); }
+
+JPH_SHIM int jph_world_bodies(void *w) { return int(static_cast<World *>(w)->sys.GetNumBodies()); }
+
+// up to cap contacts into ids (a, b pairs) and vals (x, y, z, speed); returns how many
+JPH_SHIM int jph_contacts_drain(void *w, int *ids, float *vals, int cap) {
+  Contacts &c = static_cast<World *>(w)->contacts;
+  std::lock_guard<std::mutex> g(c.lock);
+  int n = c.count < cap ? c.count : cap;
+  for (int i = 0; i < n; i++) {
+    ids[i * 2] = int(c.items[i].a);
+    ids[i * 2 + 1] = int(c.items[i].b);
+    vals[i * 4] = c.items[i].x;
+    vals[i * 4 + 1] = c.items[i].y;
+    vals[i * 4 + 2] = c.items[i].z;
+    vals[i * 4 + 3] = c.items[i].speed;
+  }
+  for (int i = n; i < c.count; i++) c.items[i - n] = c.items[i];
+  c.count -= n;
+  return n;
+}
+
+JPH_SHIM int jph_contacts_lost(void *w) { return static_cast<World *>(w)->contacts.lost; }