Pico-8 verlet integration rope - using https://www.youtube.com/watch?v=3HjO_RGIjCU

verlet.p8

pico-8 cartridge // http://www.pico-8.com
version 39
__lua__
function _init()
	mouse.init()
	
	points = {}
	sticks = {}
	
	bounce=0.9
	gravity=0.1
	friction=0.999
	
	--create points
	for i=1,11 do
		add(points,{x=i*10,y=5,oldx=i*10,oldy=5})
	end
	--links all points
	for i=2,#points do
		add(sticks,{
			p0=points[i-1],
			p1=points[i],
			len=distance(points[i-1],points[i])
			})
	end
	--pin the last point
	points[#points].pinned=true
	--move last point to middle
	points[#points].x = 64
end


function _update()

	if(btnp(⬅️)) points[#points].x-=10
	if(btnp(➡️)) points[#points].x+=10
	if(btnp(⬆️)) points[#points].y-=10
	if(btnp(⬇️)) points[#points].y+=10

	local x,y = mouse.pos()
	local b = mouse.button()
	
	if b==1 then
		points[#points].x=x
		points[#points].y=y
		points[#points].oldx=x
		points[#points].oldy=y
		points[#points].pinned=true
	end
	if btnp(❎) then
		showpoints=not showpoints
	end
	if btnp(🅾️) then
		points[#points].oldx=points[#points].x
		points[#points].oldy=points[#points].y
		points[#points].pinned=not points[#points].pinned
	end


 updatepoints()
	for i=0,2 do
		updatesticks()
		constrainpoints()
	end
end


function _draw()
	cls();
	
	rendersticks()
	if (showpoints) renderpoints()
	
	--mouse pointer
	local x,y = mouse.pos()
 --spr(0,x,y)
	pset(x,y,7)
	
	print("⬆️⬇️⬅️➡️/mouse move pinned",0,117,7)
	print("❎ show/hide points",0,123,7)
end

function distance(p0,p1)
	local dx,dy=p1.x-p0.x,p1.y-p0.y
	return sqrt(dx*dx+dy*dy)
end
-->8
--points
function updatepoints()
	for p in all(points) do
		if not p.pinned then
			local vx,vy=(p.x-p.oldx)*friction,(p.y-p.oldy)*friction
			p.oldx=p.x
			p.oldy=p.y
			p.x+=vx
			p.y+=vy
			p.y+=gravity
		end
	end
end

function constrainpoints()
	for p in all(points) do
		if not p.pinned then
			local vx,vy=(p.x-p.oldx)*friction,(p.y-p.oldy)*friction
			
			if p.x>127 then
				p.x=127
				p.oldx=p.x+vx*bounce
			elseif p.x<0 then
				p.x=0
				p.oldx=p.x+vx*bounce
			end
			if p.y>127 then
				p.y=127
				p.oldy=p.y+vy*bounce
			elseif p.y<0 then
				p.y=0
				p.oldy=p.y+vy*bounce
			end
				
		end
	end
end

function renderpoints()
	for p in all(points) do
		circfill(p.x,p.y,2,11)
	end	
end
-->8
--sticks
function updatesticks()
	for s in all(sticks) do
		local dx,dy=s.p1.x-s.p0.x,s.p1.y-s.p0.y
		local dist=sqrt(dx*dx+dy*dy)
		local diff=s.len-dist
		local perc=diff/dist/2
		local offx,offy=dx*perc,dy*perc
		
		if not s.p0.pinned then
			s.p0.x-=offx
			s.p0.y-=offy
		end
		if not s.p1.pinned then
			s.p1.x+=offx
			s.p1.y+=offy
		end
	end
end

function rendersticks()
	for s in all(sticks) do
		if not s.hidden then
			line(s.p0.x,s.p0.y,s.p1.x,s.p1.y,5)	
		end
	end
end
-->8
--mouse
--from https://www.lexaloffle.com/bbs/?tid=3549
mouse = {
  init = function()
    poke(0x5f2d, 1)
  end,
  -- return int:x, int:y, onscreen:bool
  pos = function()
    local x,y = stat(32)-1,stat(33)-1
    return stat(32)-1,stat(33)-1
  end,
  -- return int:button [0..4]
  -- 0 .. no button
  -- 1 .. left
  -- 2 .. right
  -- 4 .. middle
  button = function()
    return stat(34)
  end,
}