Pico8 Fluid Sim

fluid_sim_pico8.lua

fluid={}
poke(0x5f2d,1)

function spawndrop(x,y)
	// {x, y, old_x, old_y, hit_count}
	add(fluid,{x,y,x,y,1})
end

function sortfluid()
	for i=2,#fluid do
		local drop=fluid[i]
		for j=i-1,0,-1 do
			if j>0 and fluid[j][1]>drop[1] then
				fluid[j+1]=fluid[j]
			else
				fluid[j+1]=drop
				break
			end
		end
	end
end

function solvefluid()
	local count=#fluid
	for i,drop1 in pairs(fluid) do
		for j=i+1,count do
			drop2=fluid[j]
			if drop2[1]>drop1[1]+5 then
				break
			end
			
			local dx=drop2[1]-drop1[1]
			local dy=drop2[2]-drop1[2]
			local dist=max(dx*dx+dy*dy,1)
			if dist<25 then
				drop1[5]+=1
				drop2[5]+=1
				
				dist=sqrt(dist)
				local push=(dist-5)*.5/dist
				dx*=push
				dy*=push
				drop2[1]-=dx
				drop2[2]-=dy
				drop1[1]+=dx
				drop1[2]+=dy
			end
		end
	end
end

function movefluid()
	local mx=stat(32)-64
	local my=stat(33)-64
	for i,drop in pairs(fluid) do
		local startx=drop[1]
		local starty=drop[2]
		drop[4]-=.12/drop[5]
		
		local dx=mx-drop[1]
		local dy=my-drop[2]
		if abs(dx)+abs(dy)<40 then
			if dx*dx+dy*dy<400 then
 			local dist=max(sqrt(dx*dx+dy*dy),1)
 			drop[3]+=dx/dist*.4
 			drop[4]+=dy/dist*.4
 		end
		end
		
		drop[1]+=(drop[1]-drop[3])*.98
		drop[2]+=(drop[2]-drop[4])*.98
		
		if abs(drop[2])>64 then
			drop[2]=64*sgn(drop[2])
			drop[4]=0
		end
		if abs(drop[1])>64 then
			drop[1]=64*sgn(drop[1])
			drop[3]=0
		end
		
		drop[3]=startx
		drop[4]=starty
		
		drop[5]=1
	end
end

function _update()
	if #fluid<270 then
		spawndrop(-50+rnd(100),-64)
	end
	
	sortfluid()
	solvefluid()
	movefluid()
end

function _draw()
	camera(-64,-64)
	cls()
	for i,drop in pairs(fluid) do
		circ(drop[1],drop[2],4,13)
	end
	for i,drop in pairs(fluid) do
		circfill(drop[1],drop[2],3,1)
	end
	
	pset(stat(32)-64,stat(33)-64,7)
	
	print("cpu: "..flr(stat(1)*100).."%",-63,-63,5)
end