from visual import *

print """
Bruce Sherwood Fall 2000
Illustrates the momentum principle (Newton's 2nd law).
Click in right window, then drag force vector with
mouse button up. 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
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
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()

scene2.mouse.getclick()

while 1:
    rate(40)
    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