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Getting Vpython to run 2 moving objects is tricky as it tends to focus on only one. The answer I have used is to 'Flip-Flop' between the 2 blocks of code running each object; Set up 2 values for the flip-flop K & P. At the end of each nested 'While' P will be incramented (p=p+1). K is the remainder of P/2 (k=p%2). If k = 0 Flip! If k != 0 Flop!. I haven't got it to recognise a 'collision' event yet; & that is very Frustrating!

Python, 71 lines
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from visual import *
#VPython copes with 2 objects mooving BUT only if make it flip-flop between them!
# I have re-cycled a program from the VPython tutorial "A Ball in a Box".
#Try as I might I can't get a 'colission event' to react!
#
#    #Setting the seen, a hollow box created from 6 thin boxes.             #
wallR = box(pos=(6,0,0), size=(0.1,12,12), color=color.green, opacity=0.2)  #
walll = box(pos=(-6,0,0), size=(0.1,12,12), color=color.green, opacity=0.2) #
wallt = box(pos=(0,6,0), size=(12,0.1,12), color=color.red, opacity=0.2)    #
wallbt = box(pos=(0,-6,0), size=(12,0.1,12), color=color.red, opacity=0.2)  #
wallbk = box(pos=(0,0,-6), size=(12,12,0.1), color=color.blue, opacity=0.2) #
wallf = box(pos=(0,0,6), size=(12,12,0.1), color=color.white, opacity=0.2)  #
#
    #Creating 2 balls; position,size,colour,tail,velocity.  #
cyanball = sphere(pos=(5,5,5), radius=0.5, color=color.cyan)#
cyanball.trail = curve(color=cyanball.color)                #
cyanball.velocity = vector(3,3,3)                           #
#                                                           #
redball = sphere(pos=(-5,-5,-5), radius=0.5, color=color.red)#
redball.trail = curve(color=redball.color)                  #
redball.velocity = vector(-3,-3,-3)                         #
#
deltat = 0.005  #settig the timing.
t = 0           #
#
while t < 20:
    p=0   #Setting up 2 values for the flip-flop. At the end of each nested 'While'
    k = 0 #P will be incramented (p=p+1). K is the remainder of P/2 (k=p%2).
          #If k = 0 Flip! If k != 0 Flop!
    while k==0:
       #flipping & Running cyanball!
        cyanball.pos = cyanball.pos + cyanball.velocity*deltat
        cyanball.trail.append(pos=cyanball.pos, retain=200)
        if cyanball.pos.x < -5.6:                       #Testing for collisions
            cyanball.velocity.x = -cyanball.velocity.x  #with eack wall & bouncing!
        if cyanball.pos.x > 5.6:
            cyanball.velocity.x = -cyanball.velocity.x
        if cyanball.pos.y < -5.6:
            cyanball.velocity.y = -cyanball.velocity.y
        if cyanball.pos.y > 5.6:
            cyanball.velocity.y = -cyanball.velocity.y
        if cyanball.pos.z < -5.6:
            cyanball.velocity.z = -cyanball.velocity.z
        if cyanball.pos.z > 5.6:
            cyanball.velocity.z = -cyanball.velocity.z
        t = t + deltat
        p = p + 1
        k = p % 2
        rate(400)
       
    while k!=0:
         #Flopping & Running redball!
        redball.pos = redball.pos + redball.velocity*deltat
        redball.trail.append(pos=redball.pos, retain=200)
         
        if redball.pos.x < -5.6:
            redball.velocity.x  = -redball.velocity.x
        if redball.pos.x > 5.6:
            redball.velocity.x = -redball.velocity.x
        if redball.pos.y < -5.6:
            redball.velocity.y = -redball.velocity.y
        if redball.pos.y > 5.6:
            redball.velocity.y = -redball.velocity.y
        if redball.pos.z < -5.6:
            redball.velocity.z = -redball.velocity.z
        if redball.pos.z > 5.6:
            redball.velocity.z = -redball.velocity.z
        t = t + deltat
        p=p+1
        k = p % 2
        rate(400)

Hi I've just started teaching myself Python & Vpython. Started simple with 'A ball bouncing in a box'. Then I tried 2 balls but it wouldn't work so I ended up with this solution! But I haven't got it to recognise a 'collision' event yet; & that is very Frustrating! Any ideas? Have fun! d0m.

1 comment

Dominic Innocent (author) 10 years, 4 months ago  # | flag

Hi Yes it shows I'm a newbie! My young son took one look at this & said "why not put it all under one 'while'" & he was rite! Just goes to show the have a quicker grasp of this than us oldies {60yrs}! Have fun. d0m.

Created by Dominic Innocent on Sun, 17 Jul 2011 (MIT)
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