Doom Fire in PICO-8

Figure 1: Doom Fire from PSX implemented in PICO-8

PICO-8 was recently updated and that inspired me to get back into it. I wanted to port my favorite 2D graphics effects, the fire effect from the title screen of the PSX version of DOOM. Of course, I need to mention the very helpful guide to this effect written by Fabien Sanglard. You can checked out the HTML export of this PICO-8 port here.

It had been a year since I had written any Lua and the process of porting this effect from my C implementation was a little tricky. Many early iterations of this performed quite terribly. The limitations of PICO-8 requirement me to change the height of the effect as well as the color depth. That being said, I am happy with how it turned out.

pico-8 cartridge // http://www.pico-8.com
version 27
__lua__
-- DOOMFIRE
-- by Adam Richardson

function _init()
   fw = 128
   fh = 48
   psize = 5
   pixels = {}
   for x=0,fw do
      for y=0,fh do
         pixels[idx_xy(x,y)]=0
      end
   end

   for x=0,fw-1 do
      pixels[idx_xy(x,fh-1)]=psize
   end

   colors = {
      0,
      8,
      9,
      10,
      7,
   }

   print("doom fire", 44, 40)
end

function idx_xy(x,y)
   return y*fw+x
end

function spread(src)
   local p = pixels[src]
   if(p==0) then
      pixels[src-fw]=0
   else
      local r = band(rnd(3),3)
      local dst = src - r + 1
      pixels[dst-fw] = p-band(r,1)
   end
end

function _update()
   for x=0,fw-1 do
      for y=1,fh-1 do
         spread(idx_xy(x,y))
      end
   end
end

function _draw()
   local offset=128-fh
   for x=0,fw-1 do
      for y=0,fh-1 do
         pset(x,y+offset,colors[pixels[idx_xy(x,y)]])
      end
   end

   rectfill(0,0,128,10,0)
   print(stat(1),0,2,7)
end

Adam Richardson's Site

Doom Fire in PICO-8