particles.lua

   1
   2 particle = {list = {}}
   3 function particle:spawn (x,y,vx,vy,maxage)
   4         local p = {x=x,y=y,vx=vx,vy=vy,age=0,maxage = maxage or 10}
   5         self.list[#self.list+1] = p
   6         return p
   7 end
   8 local lut = {{0,0,0,0.3,5,t=0},{1,1,1,0.2,10,t=0.2},{0,0,1,0,50,t=1}}
   9 table.sort(lut,function(a,b) return a.t<b.t end)
  10
  11
  12 local simtime = glfw.GetTime()
  13 local updateinterval = .01
  14 function particle:step(catchup)
  15     catchup = catchup or 0
  16     local now = glfw.GetTime()
  17     if simtime+updateinterval>now then return end
  18     simtime = simtime + updateinterval
  19
  20         if math.random()>.9 then
  21                 local p = particle:spawn(200,200,(math.random()-.5),(math.random()-.4),math.random(1000,1800))
  22                 function p:think()
  23                         p.vx,p.vy = p.vx*.99,p.vy*.99-.002
  24                         local m,a = self.maxage,self.age
  25                         local p = a/m
  26
  27                         local mincol,maxcol = lut[1],lut[#lut]
  28                         for i=1,#lut do
  29                 if lut[i].t > mincol.t and lut[i].t < p then mincol = lut[i] end
  30                 if lut[i].t >= p then maxcol = lut[i] break end
  31                         end
  32                         local p = (p - mincol.t) / (maxcol.t - mincol.t)
  33                         local r1,g1,b1,a1,s1 = unpack(mincol)
  34                         local r2,g2,b2,a2,s2 = unpack(maxcol)
  35                         local q = 1-p
  36                         self.r,self.g,self.b,self.a,self.s = r1*q+r2*p, g1*q+g2*p, b1*q+b2*p, a1*q+a2*p, s1*q+s2*p
  37
  38                         if self.y < 120 then
  39                 self.vy = 0
  40                 self.vx = math.max (-0.2, math.min (0.2, self.vx * 1.03))
  41             end
  42                 end
  43                 function p:draw()
  44                         local x,y = self.x,self.y
  45                         local m,a = self.maxage,self.age
  46                         local p = 1-a/m
  47                         local s = self.s
  48             gl.Enable "COLOR"
  49                         draw.rect(x-s, y-s, s*2, s*2, self.r,self.g,self.b,self.a)
  50                 end
  51         end
  52
  53
  54         for i=#self.list,1,-1 do
  55                 local p = self.list[i]
  56                 p.x = p.x + p.vx
  57                 p.y = p.y + p.vy
  58                 p.age = p.age + 1
  59                 if p.think then p:think() end
  60                 if p.age > p.maxage then
  61                         table.remove(self.list,i)
  62                 end
  63         end
  64         local now = glfw.GetTime()
  65     if simtime+updateinterval<now then
  66         return self:step(catchup + 1)
  67     elseif catchup>1 then
  68         --print("catched up",catchup)
  69     end
  70 end
  71 function particle:draw()
  72         local rect = draw.rect
  73         for i=#self.list,1,-1 do
  74                 local p = self.list[i]
  75                 if p.draw then p:draw() else
  76                         rect(p.x-2, p.y-2, 4, 4, 1, 1, 1, 1)
  77                 end
  78         end
  79 end