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from visual import *
print """
Click to place spheres under falling string.
Right button drag to rotate view.
Middle button drag up or down to zoom in or out.
"""
scene.title = "Drape"
restlength = 0.02
m = 0.010 * restlength
g = 9.8
dt = 0.002
k = 3
damp = (1-0)**dt
nspheres = 3
floor = 0
# Create the stringy thing:
band = curve( x = arange(-1,1,restlength),
y = 1,
radius = 0.02
)
band.p = band.pos * 0
##scene.range = 1.5
##scene.autoscale = 0
# Let the user position obstacles:
spheres = []
for i in range(nspheres):
s = sphere( pos = scene.mouse.getclick().pos, #(i*0.6 - 0.7,0.5 + i*0.1,0),
radius = 0.25,
color = (abs(sin(i)),cos(i)**2,(i%10)/10.0) )
spheres.append( s )
while 1:
rate(1.0 / dt)
if scene.mouse.clicked:
i = len(spheres)
s = sphere( pos = scene.mouse.getclick().pos,
radius = 0.25,
color = (abs(sin(i)),cos(i)**2,(i%10)/10.0) )
spheres.append( s )
if floor:
below = less(band.pos[:,1],-1)
band.p[:,1] = where( below, 0, band.p[:,1] )
band.pos[:,1] = where( below, -1, band.pos[:,1] )
# need a more physical way to make 'damped springs' than this!
band.p = band.p * damp
#band.p[0] = 0 # nail down left endpoint
#band.p[-1] = 0 # nail down right endpoint
band.pos = band.pos + band.p/m*dt
#gravity
band.p[:,1] = band.p[:,1] - m * g * dt
# force[n] is the force on point n from point n+1 (to the right):
length = (band.pos[1:] - band.pos[:-1])
dist = sqrt(sum(length*length,-1))
force = k * ( dist - restlength )
force = length/dist[:,NewAxis] * force[:,NewAxis]
band.p[:-1] = band.p[:-1] + force*dt
band.p[1:] = band.p[1:] - force*dt
# color based on "stretch": blue -> white -> red
c = clip( dist/restlength * 0.5, 0, 2 )
# blue (compressed) -> white (relaxed) -> red (tension)
band.red[1:] = where( less(c,1), c, 1 )
band.green[1:] = where( less(c,1), c, 2-c )
band.blue[1:] = where( less(c,1), 1, 2-c )
for s in spheres:
dist = mag( band.pos - s.pos )[:,NewAxis]
inside = less( dist, s.radius )
if sometrue(inside):
R = ( band.pos - s.pos ) / dist
surface = s.pos + (s.radius)*R
band.pos = surface*inside + band.pos*(1-inside)
pdotR = sum(asarray(band.p)*asarray(R),-1)
band.p = band.p - R*pdotR[:,NewAxis]*inside
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