fire_fine.lua

-- accumulative random
-- allows for progressively
-- variating value instead
-- of pure random
function vrnd()
	local start = 50
	return function()
		start = start + rnd(1)* (flr(rnd(2)) == 1 and 1 or -1)
		start = mid(40,start,100)
		return start
	end
end
vrnd = vrnd()

fade_colors={
	[11]=10,
	[12]=10,
	[13]=10,
	[7]=11,
	[10]=9,
	[9]=8,
	[8]=0
}

function spal(i,v)
	poke(0x5f10+i,v)
end


spal(8,128+9)
spal(9,9)
spal(10,10)
spal(11,128+7)
spal(12,128)
spal(13,128+5)
spal(14,128+6)
-- the sprite uses green as
-- transparency
palt(3,true)
palt(0,false)

function _draw()
	-- fire effect
	-- first, make the fire
	-- rise speed vary with time
	local prt = vrnd()
	for i=0,prt*45 do
		-- let's take a random pixel
		-- so first let's take a byte
		-- in the screen memory.
	 local a=flr(rnd(0x2000))+0x6000
	 local v=peek(a)
	 -- split it in two pixels (4bits)
	 local v1=band(shr(v,4),0x0f)
	 local v2=band(v,0x0f)

		local r = 0	 
		-- if we're going to make
		-- it fade (downgrade from
		-- white to yellow to orange
		-- to black
		if rnd(5)<1 then
			-- either the first or the
			-- second pixel
		 if rnd(2)<1 then
		 	r = bor(shl(fade_colors[v1],4),v2)
		 else
		 	r = bor(shl(v1,4),fade_colors[v2])
		 end
		-- else we're just keeping
		-- the color as is.
		else
			r = v
		end		
		-- update the current pixel
	 poke(a,r)
	 -- if we can write one pixel
	 -- higher
	 if a > 0x6000+64 then
	 	-- let's do it
	 	local r2 = peek(a-64)
		 poke(a-64,r)
		end
	end

	rectfill(0,121,127,121,7)
	for i=0,2 do
		local y = 122+i*2
		rectfill(0,y,127,y+1,14-i)
	end
	spr(0,16,59,6,8)
end