REM 2D ball physics using vectors
REM Coded by: Phaelax (Phaelax@hotmail.com)
REM Website: http://www.dbspot.com/krytek/

randomize timer()

velocity# = 2

type ball
   x as float
   y as float
   r as float
   vx as float
   vy as float
   angle as float
endtype

amount = 10

dim c(amount) as ball

for i=1 to amount
   c(i).r = 20
   c(i).x = rnd(screen width()-40)+20
   c(i).y = rnd(screen height()-40)+20
   c(i).angle = rnd(360)
   c(i).vx = sin(c(i).angle) * velocity#
   c(i).vy = cos(c(i).angle) * velocity#
next i


do
   cls


   for a = 1 to amount
      for b = 1 to amount
         if a <> b
            if (c(a).x-c(b).x)^2 + (c(a).y-c(b).y)^2 <= (c(a).r+c(b).r)^2

               tx# = c(b).x - c(a).x
               ty# = c(b).y - c(a).y
               angle# = wrapvalue(atanfull(tx#, ty#)+180)
               c(a).vx = sin(angle#)*velocity#
               c(a).vy = cos(angle#)*velocity#
               c(a).angle = angle#

               tx# = c(a).x - c(b).x
               ty# = c(a).y - c(b).y
               angle# = wrapvalue(atanfull(tx#, ty#)+180)
               c(b).vx = sin(angle#)*velocity#
               c(b).vy = cos(angle#)*velocity#
               c(b).angle = angle#
            endif
         endif
      next b
   next a


   for i=1 to amount
      gosub _check_sides
      c(i).x = c(i).x + sin(c(i).angle) * velocity#
      c(i).y = c(i).y + cos(c(i).angle) * velocity#

      circle c(i).x, c(i).y, c(i).r
   next i


   set cursor 0,0
   print "FPS: ", screen fps()

loop




_check_sides:
   if (c(i).x + c(i).r >= screen width()) OR (c(i).x <= c(i).r)
      c(i).vx = c(i).vx * -1
      c(i).angle = atanfull(c(i).vx, c(i).vy)
   endif

   if (c(i).y <= c(i).r) OR (c(i).y + c(i).r >= screen height())
      c(i).vy = c(i).vy * -1
      c(i).angle = atanfull(c(i).vx, c(i).vy)
   endif

RETURN