A bouncing ball demo for the pico-8

bouncing_balls.p8

pico-8 cartridge // http://www.pico-8.com
version 39
__lua__
-- pico-8 bouncing balls demonstration
-- 2022, by j4n1x

actors={}

pstartx = 1
pendx   = 128
pstarty = 11
pendy   = 128
info = "press ❎ to add a ball"
cntinfo = "balls on screen: "

-- xa = x position
-- ya = y position
-- sa = sprite index
-- pa = transparency colours 
--						as bitfield
-- propsa = other properties
function make_actor(xa, ya, sa, pa, propsa)	
	act = {
		x = xa,
		y = ya,
		s = sa,
		p = pa or 0,
		props = propsa or {}
	}
	add(actors, act)
	return act
end

function make_ball()
	make_actor(
			rnd(pendx-pstartx-8)+pstartx, 
			rnd(pendy-pstarty-8)+pstarty,
			1, 
			0b11 << 14, 
			{
				hvel = rnd(10),
				vvel = rnd(10),
			 fcount = 0,
			 aspeed = 4,
				exec = function(act)
					if act.x + act.props.hvel + 8 > pendx  or
								act.x + act.props.hvel < pstartx then
						act.props.hvel = -act.props.hvel
					else
						act.x = act.x + act.props.hvel
					end

					if act.y + act.props.vvel + 8 > pendy or
								act.y + act.props.vvel < pstarty then
						act.props.vvel = -act.props.vvel
					else
						act.y = act.y + act.props.vvel
					end				
					act.props.fcount = act.props.fcount + 1
					if act.props.fcount == act.props.aspeed then
						act.s= ((act.s)%4)+1
						act.props.fcount = 0
					end
				end
			})
end

function draw_actor(act)
	palt(act.p)
	spr(act.s, act.x, act.y)
	if act.props["exec"] ~= nil then
		act.props["exec"](act)
	end
	palt()
end

function _init()
	infow=(128-print(info,0,-10))/2
end

function _draw()
	cls(1)
	-- help text
	rectfill(0,0,128,pstarty,0)
	print(info,infow, 0, 7)
	local cntinfow=(128-print(
			cntinfo..#actors,0, -10))/2
	print(cntinfo..#actors,
			cntinfow, 6, 7)	
	-- all actors
	foreach(actors, draw_actor)
	-- accept input
	if btnp(❎) then
		make_ball()
	end
end
	
__gfx__
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