pico-8 cartridge // http://www.pico-8.com
version 42
__lua__

function _init()
	cmgr0=cloud_manager:new(15,51,5,1,5,13)
	cmgr1=cloud_manager:new(12,51-8,7,4,13,6)
	cmgr2=cloud_manager:new(6,51-14,9,3,15,7)
	cmgr0.step=5
	cmgr1.step=4
	cmgr2.step=3
 last_x=0
 x=0
 dx=0
end


function _update60()
 if (btn(4)) dx+=1.0
 dx*=0.75
 x+=dx
 while last_x<x do
		cmgr0:update()
		cmgr1:update()
		cmgr2:update()
		last_x+=1
	end
end

function _draw()
 cls(12)
	cmgr0:draw()
	cmgr1:draw()
	cmgr2:draw()
end

cloud_manager={}
function cloud_manager:new(sparseness,y,h,oval_h,c0,c1)
 local c={
		frame=0,
		clouds={},
		bitplanes=split"241,242,244,248",
		step=1,
		sparseness=sparseness,
		y=y,
		c0=c0,
		c1=c1,
		h=h,
		oval_h=oval_h
	}
	setmetatable(c,{__index=cloud_manager})
	return c
end

function cloud_manager:update()
 self.frame+=1
	if self.frame%(self.step*self.sparseness) == 0 then
	 local bp=deli(self.bitplanes,1)
		add(self.clouds,{x=127,y=rnd()*self.h,w=flr(rnd()*16)+16,plane=bp})
		add(self.bitplanes,bp)
	end
	 
	if self.frame%self.step==0 then
	 local clouds2={}
	 for c in all(self.clouds) do
	  c.x-=1
	  if (c.x+c.w>0) add(clouds2,c)
	 end
	 self.clouds=clouds2
	end
end

function cloud_manager:draw()
	local r0=96
	local r1=96+16
	local h=self.h+self.oval_h+1
	assert(h<=16)

	-- render to spritesheet
	poke(0x5f55,0x00)
	rectfill(0,r0,127,r0+h,0)
	
	-- use bitplanes
	for c in all(self.clouds) do
		poke(0x5f5e,c.plane)
		ovalfill(c.x,r0+c.y,c.x+c.w,r0+c.y+self.oval_h,15)
	end
	poke(0x5f5e,255)
	
	-- render from high memory
	-- to higher memory
	rectfill(0,r1,127,r1+h,0)
	
	for i in all(split"0,1,2,4,8") do
		palt(i,true)
	end
	for i=0,15 do
		pal(i,7)
	end
	
	poke(0x5f5e,0xf1)
	sspr(0,r0,128,h,0,r1) 
	poke(0x5f5e,0xf2)
	sspr(0,r0,128,h,1,r1+1) 
	sspr(0,r0,128,h,5,r1+1) 
	poke(0x5f5e,255)
	
	-- render to screen
	poke(0x5f55,0x60)
	pal()
	pal(1,self.c1)
	pal(2,self.c0)
	pal(3,self.c1)
	sspr(0,r1,128,h,0,self.y)
	pal()
end

__gfx__
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
00700700000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
00077000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
00077000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
00700700000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000