carcontroller.lua

-- This object takes care of controlling the NPC cars.

-- List of cars that we control that are currently driving.
-- Fields:
--   thing: the car Thing
--   speed: the car's absolute speed (always positive)
--   lane: the car's lane (1,2 for northbound, -1,-2 southbound)
local fleet = {}

-- List of cars that we control that are currently
-- invisible waiting for placement. This is a list of
-- just the Thing objects, not tables.
local garage = {
  getThing("CAR 0"), getThing("CAR 1"), getThing("CAR 2"),
  getThing("CAR 3"), getThing("CAR 4"), getThing("CAR 5"),
  getThing("CAR 6"), getThing("CAR 7"), getThing("CAR 8")
}

-- How far ahead of the player we spawn cars.
local SPAWN_DIST = 400

-- Car speeds
local SPEED_MIN, SPEED_MAX = 4, 5

-- World Z coordinate beyond which we despawn.
local DESPAWN_PLUS_Z = 600
local DESPAWN_MINUS_Z = -200

-- Starting number of cars.
local BASE_NUM_CARS = 2
-- Add a new car every how many meters driven?
local ADD_CAR_EVERY_M = 200

local crashed = false

-- Distance traveled so far by the player.
local traveledM = 0

-- The "forward" velocity along the road is given
-- by the world position of the "Forward" object, which is
-- set to local position (0,0,1) in the Road.
local FWD_X, FWD_Y, FWD_Z =
  getThing("Forward"):getPosition()

-- Countdown to the next time we will do a slowdown
-- check to stop cars from colliding
local SLOW_CHECK_INTERVAL = 60
local countdownToSlowCheck = SLOW_CHECK_INTERVAL

function onUpdate()
  if crashed then return end

  -- Iterate backwards so we can remove as we go.
  for i = #fleet, 1, -1 do
    local e = fleet[i]
    local x, y, z = e.thing:getLocalPosition()
    local dir = e.lane > 0 and 1 or -1
    -- Move the car. This is based on its speed and the
    -- direction of motion which depends on whether it's
    -- driving northbound or southbound.
    z = z + e.speed * dir
    e.thing:setLocalPosition(x, y, z)
    x, y, z = e.thing:getPosition()
    -- If the car gets too far away, despawn it.
    if z > DESPAWN_PLUS_Z or z < DESPAWN_MINUS_Z then
      removeFromFleet(i)
    end
  end

  -- How many cars do we want to have on the fleet?
  local desiredNumCars = BASE_NUM_CARS +
    floor(traveledM / ADD_CAR_EVERY_M)

  -- If we have fewer cars than we want to, try to spawn.
  if #fleet < desiredNumCars then
    -- If we can, spawn a new car.
    trySpawnCar((randomFloat() > 0.5 and 1 or -1) *
      randomBetween(1, 2))
  end

  countdownToSlowCheck = countdownToSlowCheck - 1
  if countdownToSlowCheck < 1 then
    countdownToSlowCheck = SLOW_CHECK_INTERVAL
    doSlowCheck()
  end
end

-- Removes the car from the active fleet, putting it back
-- into the inactive list (garage).
function removeFromFleet(i)
  local fleetEntry = remove(fleet, i)
  -- Back into the garage you go.
  insert(garage, fleetEntry.thing)
  fleetEntry.thing:setLocalPosition(0, 0, -100000) -- hide
end

-- Tries to spawn a car.
function trySpawnCar(lane)
  if #garage < 1 then return end  -- Nothing to spawn
  local rx, ry, rz =
    getThing("Road"):getLocalPosition()
  -- The player's position relative to the road is -rz,
  -- as the road moves backward under the player.
  local playerOnRoadZ = -rz
  -- We want to spawn cars SPAWN_DIST ahead of the player
  -- so this is this Z position at which we want to spawn.
  local spawnZ = SPAWN_DIST + playerOnRoadZ
  -- Check if we conflict with any car.
  for i = 1, #fleet do
    local lx, ly, lz = fleet[i].thing:getLocalPosition()
    if fleet[i].lane == lane and abs(lz - spawnZ) < 60 then
      -- Conflict! Don't spawn.
      return
    end
  end
  -- If we got here, it's all clear to spawn.
  local newCar = remove(garage, 1)
  newCar:setLocalPosition(getLaneLocalX(lane),1,spawnZ)
  newCar:setLocalRotation(0,lane > 0 and 0 or 180,0)
  -- Set a random-ish speed.
  local speed = SPEED_MIN + randomFloat() * (SPEED_MAX - SPEED_MIN)
  -- If traveling southbound, cut the speed by half so the
  -- player doesn't crash as easily.
  if lane < 0 then speed = speed * 0.5 end
  insert(fleet, {thing=newCar, speed=speed, lane=lane})
end

-- Returns the local X coordinate for cars on the given
-- lane number.
function getLaneLocalX(lane)
  return 15 * lane + (lane > 0 and -5 or 5)
end

function onCrashed()
  crashed = true
end

function onSetTraveledDist(msg)
  traveledM = msg.traveledM
end

-- Checks to see if any two cars on the same lane are too close,
-- in which case we tell the faster one to slow down to the
-- speed of the slower one.
function doSlowCheck()
  for i = 1, #fleet do
    if fleet[i].lane > 0 then
      local inFront = getCarInFront(i)
      -- If the car in front is going slower than us, slow down
      -- to match its speed so we don't crash into it.
      if inFront and inFront.speed < fleet[i].speed then
        fleet[i].speed = inFront.speed
      end
    end
  end
end

-- Gets the car that's directly in front of this one,
-- or nil if none.
function getCarInFront(carIndex)
  local car = fleet[carIndex]
  local carX, carY, carZ = car.thing:getLocalPosition()
  -- We're looking for a car in the same lane and with
  -- this range of Z positions:
  local minZ, maxZ = carZ, carZ + 120

  for i = 1, #fleet do
    local thisCar = fleet[i]
    if i ~= carIndex and thisCar.lane == car.lane then
      local x, y, z = thisCar.thing:getLocalPosition()
      if z >= minZ and z <= maxZ then return thisCar end
    end
  end
end

function onGameOver()
  -- Hide all cars
  for i = 1, #fleet do
    fleet[i].thing:setPosition(-10000, -10000, -10000)
  end
end

-- All cars in the garage start hidden.
for i = 1, #garage do garage[i]:setPosition(0,0,-1000000) end