from visual import *

print """
Bruce Sherwood Fall 2000
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.
"""

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=(-0.9*wide,0,0), radius=wide/20, color=color.cyan)
ball.mass = 200.
ball.p = vector()
trail = curve(color=ball.color)
dt = 0.1
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 = 0.05 # 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)
scene.select()

drag = 0
F = vector(0,0,0)
while 1:
    rate(40)
    if scene2.mouse.events:
        m = scene2.mouse.getevent()
        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
    trail.append(pos=ball.pos)
    if not (-wide <= ball.x <= wide):
        trail.visible = 0
        trail = curve(color=ball.color)
        if ball.p.x > 0:
            ball.x = -wide
        else:
            ball.x = wide
    if not (-wide <= ball.y <= wide):
        trail.visible = 0
        trail = curve(color=ball.color)
        if ball.p.y > 0:
            ball.y = -wide
        else:
            ball.y = wide
    Fvec.pos = ball.pos+Foffset
    Fvec.axis = Fview*F
    pvec.pos = ball.pos
    pvec.axis = pview*ball.p