from __future__ import print_function, division
from visual import *

print("""
Bruce Sherwood Fall 2000
Revised Spring 2005 to display against a moving background.
Illustrates the momentum principle (Newton's 2nd law).
In right window, drag the force vector.
Object in left window moves under the influence
of this single force, and bounces off the walls.
""")

h = w = 500
scene.width = w
scene.height = h
scene.x = scene.y = 0
wide = 1.
scene.fov = 0.001
scene.range = wide
scene.userzoom = 0
scene.userspin = 0
ball = sphere(pos=(0,0,0), radius=wide/20, color=color.cyan)
ball.mass = 200.
ball.p = vector()
mpos = vector(0,0,0)
grid = frame()
trail = curve(frame=grid, color=ball.color)
gridd = 0.5*wide
gridr = 2*wide+gridd
R = .01*gridd
for x in arange(-gridr,gridr+gridd/2,gridd):
    curve(frame=grid, pos=[(x,-gridr,0),(x,gridr,0)], radius=R)
for y in arange(-gridr,gridr+gridd/2,gridd):
    curve(frame=grid, pos=[(-gridr,y,0),(gridr,y,0)], radius=R)
dt = 0.02
Foffset = vector(0,0,-ball.radius)
Fvec = arrow(pos=ball.pos+Foffset, axis=(0,0,0), shaftwidth=wide/30., color=color.green)
pvec = arrow(pos=ball.pos, axis=(0,0,0), shaftwidth=wide/30., color=color.red)
Fmouse = 1. # F mouse scale factor
Fview = 1. # F view scale factor
pview = 0.025 # p view scale factor

scene2 = display(x=w, y=0, width=w, height=h)
scene2.range = wide
scene2.userzoom = 0
scene2.userspin = 0
Fvec2 = arrow(display=scene2, axis=(0,0,0), shaftwidth=wide/30., color=color.green)
sphere(display=scene2, radius=Fvec2.shaftwidth/2., color=Fvec2.color)

drag = 0
F = vector(0,0,0)
count = 0
while 1:
    rate(200)
    if scene2.mouse.events: # check for mouse events
        m = scene2.mouse.getevent() # get the mouse info
        if m.drag == 'left' or m.press == 'left':
            drag = 1
        elif m.drop == 'left':
            drag = 0
    if drag:
        F = Fmouse*scene2.mouse.pos
    Fvec2.axis = Fview*F
    ball.p = ball.p + F*dt
    ball.pos = ball.pos + (ball.p/ball.mass)*dt
    scene.center = ball.pos # follow the ball, keeping it in the center
    trail.append(pos=ball.pos)
    if abs(ball.pos.x) >= gridr:
        ball.p.x = -ball.p.x
    if abs(ball.pos.y) >= gridr:
        ball.p.y = -ball.p.y
    Fvec.pos = ball.pos
    Fvec.axis = Fview*F
    pvec.pos = ball.pos
    pvec.axis = pview*ball.p