simple particle engine

10 hgr : hcolor = 3

21 sx = 140
22 sy = 96
23 g = 0.5
24 n = 30
35 dim vx(n) : dim vy(n)
40 dim age(n)
45 dim exist(n)

199Poke230,32:gosub 200:Poke49236,0:poke 230,64:gosub200:poke49237,0:goto199
200fr=fr+1:?"frame ";fr;", pn ";pn:call-3086
205 gosub 1000 : rem add particle
207 for i = 1 to n : if exist(i) = 1 then gosub 2000 : rem calc and draw
208 next i
210

999 return

1000 rem add particle
1005 done = 0
1010 for i = 1 to n
1020 if exist(i) = 0 then exist(i) = 1 : vx(i) = int(rnd(1)*10)-5 : vy(i) = int(rnd(1)*10)-5 : age(i) = 0 : pn = pn + 1 : done = 1
1100 if done = 0 then next i
1110 return

2000 rem calc and draw
2010 age(i) = age(i) + 0.3
2013 nx = sx+(vx(i)*age(i)) : ny = sy+(vy(i)*age(i))+(g*(age(i)*age(i))/2)
2015 if nx < 0 or nx>279 or ny<0 or ny>159 then exist(i) = 0 : pn = pn - 1 : return
2020 hplot nx,ny : return