def update(self, dt):
"""Updates the position and the velocity of the shell.
Moves the shell based on it's current velocity and the time passed (`dt`).
Updates the velocity based on `self.gravity`, `self.wind`, `self.drag_coef` and the time passed.
Args:
dt: Delta t, the change of time the shell should be updated by.
"""
# move the shell based on the current velocity and change of time
self.center = Vector(*self.center) + Vector(*self.velocity) * dt
# apply gravitational acceleration
self.velocity_y -= self.gravity * dt
air_vel = Vector(self.velocity_x - self.wind, self.velocity_y)
# based on https://en.wikipedia.org/wiki/Drag_equation
# hides the density, area and other constants for the shell into the drag coefficient
drag = air_vel.normalize() * self.drag_coef * air_vel.length2()
vel_vec = Vector(*self.velocity) - (drag / self.mass)
self.velocity = (vel_vec.x, vel_vec.y)
# bounce off the walls
if (self.x < 0) or (self.right > self.parent.width):
self.velocity_x *= -1
self.right = clamp(self.right, 0, self.parent.width)
self.x = clamp(self.x, 0, self.parent.width)
if self.top > self.parent.height:
self.velocity_y *= -1
self.top = clamp(self.top, 0, self.parent.height)
def gravitate_towards(self, body):
velocity_v = Vector(self.velocity)
gravity_v = Vector(body.pos) - Vector(self.pos)
self.velocity = velocity_v + \
(gravity_v * 1. / gravity_v.length2()) * body.mass
def gravitate_towards(self, body):
velocity_v = Vector(self.velocity)
gravity_v = Vector(body.pos) - Vector(self.pos)
self.velocity = velocity_v + (gravity_v * 1.0 / gravity_v.length2()) * body.mass