feat(vehicles): 16.7 - a boat is a buoyant hull in the game's physics (VehicleHull), rowed along its bow and turned by the oars; the scripted bob, the wind's drift and the shore refusal are gone

The water floats the hull, the wind pushes every boat as a force, the lake bed stops it at the shore;
the swell takes the outward share of a stroke. ludic.physics: phys_hull_add (a buoyant box),
phys_row, phys_bow_speed, and a test that floats one a quarter under, rows, turns and grounds it.
The vehicles tests row a real Jolt hull on the fake shore; the horse moved to horse.ludic.

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

packages/ludic.physics/hull.ludic

@@ -0,0 +1,26 @@
+# hull.ludic - a boat: a buoyant box floated by PhysWater, rowed along its bow and turned about its
+# middle. Its bow is -z at yaw 0, the way the valley faces (forward is (-sin yaw, -cos yaw)).
+
+# hx, hy, hz its half width, depth and length; buoyancy over 1 floats it (4: a quarter under)
+export function phys_hull_add(physics_st: mut PhysicsState, x: float, y: float, z: float, yaw: float, hx: float, hy: float, hz: float, mass: float, buoyancy: float, drag: float) -> int {
+  let id = phys_body_add(physics_st, phys_box(physics_st, hx, hy, hz), x, y, z, yaw, mass)
+  if id < 0 { return -1 }
+  phys_float(physics_st, id, buoyancy, drag, drag * 1.5)
+  return id
+}
+
+# a stroke of `forward` newtons along the bow and a turn of `turn` newton-metres about y, over the
+# next step
+export function phys_row(physics_st: mut PhysicsState, id: int, forward: float, turn: float) -> void {
+  let p = phys_pose(physics_st, id)
+  if p == null { return }
+  let yaw = phys_yaw_of(p)
+  phys_force(physics_st, id, -Math.sin(yaw) * forward, 0.0, -Math.cos(yaw) * forward)
+  phys_torque(physics_st, id, 0.0, turn, 0.0)
+}
+
+# how fast it goes along its bow (backwards is negative)
+export function phys_bow_speed(p: PhysPose) -> float {
+  let yaw = phys_yaw_of(p)
+  return -Math.sin(yaw) * p.vx - Math.cos(yaw) * p.vz
+}

packages/ludic.physics/index.ludic

@@ -10,4 +10,5 @@ import "bodies.ludic"
 import "queries.ludic"
 import "water.ludic"
 import "walker.ludic"
+import "hull.ludic"
 import "system.ludic"

packages/ludic.physics/tests/motion_test.ludic

@@ -127,4 +127,34 @@ program MotionTest {
     expect_eq(float_bits(a.z), float_bits(b.z))
     expect_eq(float_bits(a.qw), float_bits(b.qw))
   }
+
+  test "a hull floats a quarter under, is rowed along its bow, turned, and stopped by the lake bed" (physics_st: mut PhysicsState) {
+    world(physics_st)
+    let b = phys_hull_add(physics_st, 40.0, 0.5, 0.0, 1.5707963, 0.6, 0.25, 1.9, 180.0, 4.0, 1.0)
+    sim(physics_st, 4.0)
+    let p0 = phys_pose(physics_st, b)
+    expect(p0.y > -0.2)
+    expect(p0.y < 0.2)
+    for i in 0 .. 240 {
+      phys_row(physics_st, b, 420.0, 0.0)
+      phys_step(physics_st)
+    }
+    let p1 = phys_pose(physics_st, b)
+    expect(p1.x < 34.0)
+    expect(phys_bow_speed(p1) > 1.0)
+    for i in 0 .. 120 {
+      phys_row(physics_st, b, 0.0, 520.0)
+      phys_step(physics_st)
+    }
+    expect(Math.abs(phys_yaw_of(phys_pose(physics_st, b)) - phys_yaw_of(p1)) > 0.5)
+    phys_close(physics_st)
+    world(physics_st)
+    let c = phys_hull_add(physics_st, 24.0, 0.5, 0.0, 1.5707963, 0.6, 0.25, 1.9, 180.0, 4.0, 1.0)
+    for i in 0 .. 600 {
+      phys_row(physics_st, c, 420.0, 0.0)
+      phys_step(physics_st)
+    }
+    expect(phys_pose(physics_st, c).x > 19.5)
+    phys_close(physics_st)
+  }
 }