def sim_fn(g: Plotter):
env = g.entity(components=[Action, State])
car = g.entity(components=[Velocity, Position])
# process car physics
# compute velocity based on acceleration action & decceleration due to gravity
acceleration, gravity, max_speed = 0.001, 0.0025, 0.07
# apply acceleration based on accelerate action:
# 0: Accelerate to the Left
# 1: Don't accelerate
# 2: Accelerate to the Right
car[Velocity].x += (env[Action].accelerate - 1) * acceleration
# apply gravity inverse to the mountain path used by the car
# the mountain is defined by y = sin(3*x)
# as such we apply gravity inversely using y = cos(3*x)
# apply negative gravity as gravity works in the opposite direction of movement
car[Velocity].x += g.cos(3 * car[Position].x) * (-gravity)
car[Velocity].x = g.clip(car[Velocity].x,
min_x=-max_speed,
max_x=max_speed)
# compute new position from current velocity
min_position, max_position = -1.2, 0.6
car[Position].x += car[Velocity].x
car[Position].x = g.clip(car[Position].x, min_position, max_position)
# collision: stop car when colliding with min_position
if car[Position].x <= min_position:
car[Velocity].x = 0.0
# resolve simulation state: reward and simulation completition
env[State].reward = 0 if car[Position].x >= 0.5 else -1
env[State].ended = True if car[Position].x > 0.5 else False
def physics_sys(g: Plotter):
# compute velocity from car's rotation and speed
car = g.entity(components=[Movement, Velocity, Position, Meta])
# rotation
heading_x, heading_y = g.cos(
car[Movement].rotation), -g.sin(car[Movement].rotation)
# speed
car[Velocity].x = car[Movement].speed * heading_x
car[Velocity].y = car[Movement].speed * heading_y
# update car position based on current velocity
car[Position].x += car[Velocity].x
car[Position].y += car[Velocity].y