### doppler-Wavefront.py
### Doppler Effect for Sound (requires VPython)
### Rob Salgado
### salgado@physics.syr.edu     http://physics.syr.edu/~salgado/
###
### v0.5  2007-02-27 tested on Windows XP/TabletPC
###         with Python-2.3.4.exe and VPython-2003-10-15.exe

from visual import *

vs=0.20 #velocity of the source
vr=-0.30 #velocity of the receiver
vw=0.10 #velocity of the wind

scene=display(x=0,y=0,height=700,width=700)
scene.autoscale=0

source=sphere(radius=0.2,   pos=vector(0,0,0), vel=vector(vs,0,0), color=color.red)
receiver=sphere(radius=0.2, pos=vector(3,0,0), vel=vector(vr,0,0), color=color.green)
diffx=receiver.x-source.x
if diffx==0:
    signdiffx=0
elif diffx==fabs(diffx):
    signdiffx=1
else:
    signdiffx=-1
windvel=vector(vw,0,0)


nudge=vector(0,6,0)
nudgev=vector(0,0.5,0)

vsarrow=arrow(pos=source.pos+nudge ,axis=5*vector(vs,0,0) , fixedwidth=1, shaftwidth=0.1,  color=source.color)
vrarrow=arrow(pos=receiver.pos+nudge-nudgev ,axis=5*vector(vr,0,0),fixedwidth=1 ,shaftwidth=0.1, color=receiver.color)
if vw != 0: vwarrow=arrow(pos=nudge+2*vector(0,1,0) ,axis=5*vector(vw,0,0),fixedwidth=1 ,shaftwidth=0.1, color=color.cyan)

vslabel=label(pos=vsarrow.pos+nudge ,text="%4.2f" %vs , color=source.color,box=1)
vrlabel=label(pos=vrarrow.pos-nudgev ,text="%4.2f" %vr , color=receiver.color)
if vw != 0: vwlabel=label(pos=vwarrow.pos+vector(0,1,0) ,text="wind speed= %4.2f" %vw , color=vwarrow.color)


tmax=12.
dt=0.005
twopi=2*math.pi
N=32

ball=[]
ball0flag=[]
sourcelabel=[]
receivedlabel=[]

def new_wave(t):
    ball0flag.append(0)
    sphere(radius=0.05, pos=source.pos, color=(.5,0,0) )
    sphere(radius=0.05, pos=receiver.pos, color=(0,.5,0) )

    for i in range(0,N):
        theta=twopi*i/float(N)
        ball.append(sphere(radius=0.1,pos=source.pos,
                           vel=vector(cos(theta),sin(theta),0) ))
    sourcelabel.append( label(pos=ball[N*(len(ball0flag)-1)+3*N/4].pos, text="%4.2f" %t,
                                        color=source.color, linecolor=source.color ))
def meeting(t):
    global signdiffx
    label(pos=source.pos+nudge-nudgev/2.0, text="(%4.2f)" %t,
                color=color.white, linecolor=color.white )
    print  "(%4.2f)" %t
    signdiffx=2

print "successive wavefronts received at time..."
new_wave(0)
told=0
#clock=label()
for t in arange(0,tmax+dt,dt):
    rate(100)

#    clock.text="%f" % (t%1.0)
    if t%1.0 < told%1.0:
#        print "t=",t, "len=",len(ball)
        new_wave(t)

    told=t
    
    if signdiffx==0:
        if fabs(receiver.x-source.x)>0: meeting(t)
    elif signdiffx==1:
        if (receiver.x-source.x)<=0: meeting(t)
    elif signdiffx==-1:
        if (receiver.x-source.x)>=0: meeting(t)
    
    for i in arange(len(ball)):
        ball[i].pos += (ball[i].vel+windvel)*dt
    source.pos += source.vel * dt
    receiver.pos += receiver.vel * dt

    vsarrow.pos=source.pos+nudge
    vrarrow.pos=receiver.pos+nudge-nudgev
    
    vslabel.pos=vsarrow.pos+nudgev
    vrlabel.pos=vrarrow.pos-nudgev
    
    for j in arange(len(ball0flag)):
        sourcelabel[j].pos=ball[N*j+3*N/4 ].pos
        if (ball0flag[j]==0 and
            ( (receiver.x >= source.x and ball[N*j].x >= receiver.x)
            or (receiver.x <= source.x and ball[N*j+N/2].x < receiver.x) 
            )):
                ball0flag[j]=1
                print "%4.2f" %t
                receivedlabel.append( label(pos=ball[N*j+(N-3)].pos, text="%4.2f" %t,
                                            color=receiver.color, linecolor=receiver.color ))
        elif ball0flag[j]==1:
            receivedlabel[j].pos=ball[N*j+(N-3) ].pos
            

#Now... WHEN AN OBJECT IS PICKED,
#TRANSLATE THE scene.center TO THE OBJECT'S POSITION, THEN ZOOM        
while 1:
    rate(5)
    if scene.mouse.clicked:
        scene.mouse.getclick()
        
        newPick=scene.mouse.pick
        if newPick !=None:
            tempcolor=newPick.color
            newPick.color=color.yellow
            #pick_r=newPick.x*4.
            #string= "r=%7.5f" % pick_r
            #label(pos=newPick.pos,text=string,xoffset=-5,yoffset=5)
            
            target=newPick.pos
            step=(target-scene.center)/20.
            for i in arange(1,20,1):
                rate(10)
                scene.center +=step
                scene.scale *= 1.037  #(1.037**19=1.99)
            newPick.color=tempcolor