# ball physics code for generic 2D domain
# the functions inside() and normal() encode the shape of the ennvironment
import simplegui
import random
import math
# Canvas size
width = 600
height = 400
# Ball traits
radius = 20
color = "White"
# math helper function
def dot(v, w):
return v[0] * w[0] + v[1] * w[1]
class RectangularDomain:
def __init__(self, width, height):
self.width = width
self.height = height
self.border = 2
# return if bounding circle is inside the domain
def inside(self, center, radius):
in_width = ((radius + self.border) < center[0] <
(self.width - self.border - radius))
in_height = ((radius + self.border) < center[1] <
(self.height - self.border - radius))
return in_width and in_height
# return a unit normal to the domain boundary point nearest center
def normal(self, center):
left_dist = center[0]
right_dist = self.width - center[0]
top_dist = center[1]
bottom_dist = self.height - center[1]
if left_dist < min(right_dist, top_dist, bottom_dist):
return (1, 0)
elif right_dist < min(left_dist, top_dist, bottom_dist):
return (-1, 0)
elif top_dist < min(bottom_dist, left_dist, right_dist):
return (0, 1)
else:
return (0, -1)
# return random location
def random_pos(self, radius):
x = random.randrange(radius, self.width - radius - self.border)
y = random.randrange(radius, self.height - radius - self.border)
return [x, y]
# Draw boundary of domain
def draw(self, canvas):
canvas.draw_polygon([[0, 0], [self.width, 0],
[self.width, self.height], [0, self.height]],
self.border*2, "Red")
class CircularDomain:
def __init__(self, center, radius):
self.center = center
self.radius = radius
self.border = 2
# return if bounding circle is inside the domain
def inside(self, center, radius):
dx = center[0] - self.center[0]
dy = center[1] - self.center[1]
dr = math.sqrt(dx ** 2 + dy ** 2)
return dr < (self.radius - radius - self.border)
# return a unit normal to the domain boundary point nearest center
def normal(self, center):
dx = center[0] - self.center[0]
dy = center[1] - self.center[1]
dr = math.sqrt(dx ** 2 + dy ** 2)
return [dx / dr, dy / dr]
# return random location
def random_pos(self, radius):
r = random.random() * (self.radius - radius - self.border)
theta = random.random() * 2 * math.pi
x = r * math.cos(theta) + self.center[0]
y = r * math.sin(theta) + self.center[1]
return [x, y]
# Draw boundary of domain
def draw(self, canvas):
canvas.draw_circle(self.center, self.radius, self.border*2, "Red")
class Ball:
def __init__(self, radius, color, domain):
self.radius = radius
self.color = color
self.domain = domain
self.pos = self.domain.random_pos(self.radius)
self.vel = [random.random() + .1, random.random() + .1]
# bounce
def reflect(self):
norm = self.domain.normal(self.pos)
norm_length = dot(self.vel, norm)
self.vel[0] = self.vel[0] - 2 * norm_length * norm[0]
self.vel[1] = self.vel[1] - 2 * norm_length * norm[1]
# update ball position
def update(self):
self.pos[0] += self.vel[0]
self.pos[1] += self.vel[1]
if not self.domain.inside(self.pos, self.radius):
self.reflect()
# draw
def draw(self, canvas):
canvas.draw_circle(self.pos, self.radius, 1,
self.color, self.color)
# generic update code for ball physics
def draw(canvas):
ball.update()
field.draw(canvas)
ball.draw(canvas)
field = RectangularDomain(width, height)
# field = CircularDomain([width/2, height/2], 180)
ball = Ball(radius, color, field)
frame = simplegui.create_frame("Ball physics", width, height)
frame.set_draw_handler(draw)
frame.start()
