# legs.ludic - a horse's legs in the world's physics (Maroon Lake: a Jolt walker), named by the
# vehicle's nid. Gravity, steps, slopes and whatever stands in its way are theirs; unbound, the
# ground is walked as it is, a rise steeper than it can take stops it and nothing else is in the way.
export port VehicleLegs {
  walk: fn(int, float, float, float, float, float, float) -> bool = fn ve__walk   # (nid, x, y, z, vx, vz, dt): its pose into x, y, z
  x: fn() -> float = fn ve__lx
  y: fn() -> float = fn ve__ly
  z: fn() -> float = fn ve__lz
  stand: fn(int, float, float, float) -> void = fn ve__stand   # (nid, x, y, z): tied or led there
  gone: fn(int) -> void = fn ve__legs_gone
}

function ve__walk(vehicles_st: mut VehiclesState, nid: int, x: float, y: float, z: float, vx: float, vz: float, dt: float) -> bool {
  vehicles_st.ve_lx = x
  vehicles_st.ve_ly = y
  vehicles_st.ve_lz = z
  let nx = x + vx * dt
  let nz = z + vz * dt
  let nh = VehicleWorld.ground(nx, nz)
  if nh - y > Math.sqrt(vx * vx + vz * vz) * dt * 0.9 { return true }
  vehicles_st.ve_lx = nx
  vehicles_st.ve_ly = nh
  vehicles_st.ve_lz = nz
  return true
}
function ve__lx(vehicles_st: VehiclesState) -> float { return vehicles_st.ve_lx }
function ve__ly(vehicles_st: VehiclesState) -> float { return vehicles_st.ve_ly }
function ve__lz(vehicles_st: VehiclesState) -> float { return vehicles_st.ve_lz }
function ve__stand(nid: int, x: float, y: float, z: float) -> void { }
function ve__legs_gone(nid: int) -> void { }