#!/usr/bin/python

from play import *

paper_w = 750 ; paper_h = 550

paper(paper_w, paper_h, "white")
real_width = 5

scale = paper_w / real_width
yoffset = paper_h / 2

g = -9.8

dt = 0.003

x = 0 ; y = 0
vx = 11.56 ; vy = 3.39

t = 0
tmax = 5

drag_factor = 0.2 # bogus, supposed to be proportional to cross section area
lift_factor = 0.08

spin = 100  # revs per second? top spin is positive

while t < tmax:
	point(x*scale, y*scale + yoffset)
	
	ax = 0
	ay = g

	v = hypot(vx, vy)

	# drag
	drag = drag_factor * v*v
	dragx = -vx/v * drag
	dragy = -vy/v * drag

	ax = ax + dragx
	ay = ay + dragy

	# lift
	upx = -vy/v
	upy = vx/v
	liftx = upx * lift_factor * spin * v
	lifty = upy * lift_factor * spin * v

	ax = ax + liftx
	ay = ay + lifty

#	adrag = fudge_drag * v

	x = x + vx * dt
	y = y + vy * dt

	vx = vx + ax * dt
	vy = vy + ay * dt

	t = t + dt

pause()


# def tree(x, y, a, r, depth):
# 	if depth == 0:
# 		circle(x, y, r/2, fill="green")
# 	else:
# 		nx = x + r*sin(a)
# 		ny = y + r*cos(a)
# 		line(x, y, nx, ny, width=r/6, fill="brown")
# 		tree(nx, ny, a-30, r*3/4, depth-1)
# 		tree(nx, ny, a+25, r*3/4, depth-1)
# 
# for depth in range(0, 9):
# 	tree(200, 50, 0, 70, depth)
# 	pause()
# 	clear()