btnq.lua

--
-- UPDATE 2022-02-23
-- blog post about input buffering: https://pancelor.tumblr.com/post/677053912115707904/input-buffering-in-grid-based-games
--


--
-- button queue
--
-- requires:
-- * btnp(b): returns whether button b (0-3) was pressed this frame
-- * btnr(b): returns whether button b was released this frame
--
-- I used a version of this in ocelotsafari.p8:
-- https://github.com/pancelor/ocelot-safari/blob/main/1.lua
--

btnq={}
-- update button queue tracking
-- call this at the start of each frame
function update_btnq()
 for b=0,3 do
  if btnp(b) then
   add(btnq,{b=b})
  end
 end

 for e in all(btnq) do
  if btnr(e.b) then
   e.rm=true
  end
 end
end

-- get the next button (0-3 or nil)
function poll_btnq()
 -- delayed button release
 for e in all(btnq) do
  if e.rm and e.seen then
   del(btnq,e)
  end
 end
 --find first unseen entry, or last entry
 for i,e in ipairs(btnq) do
  if not e.seen or i==#btnq then
   e.seen=true
   return e.b
  end
 end
end

-- has any queued button not been seen yet?
function any_btnq()
 for e in all(btnq) do
  if not e.seen then
   return true
  end
 end
end

--
-- usage example:
--

function approach(x,target,delta)
 delta=delta or 1
 return x<target and min(x+delta,target) or max(x-delta,target)
end

function _init()
 -- button->x,y mappings.
 -- e.g. pressing button 1 should make you move right, so dirx[1] is 1 and diry[1] is 0
 dirx={1,0,0}
 dirx[0]=-1
 diry={0,-1,1}
 diry[0]=0

 x,y=64,64 --current position
 x1,y1=x,y --goal position
end

function _update()
  update_btnq()

 -- move towards goal position
 -- move faster if there are unseen buttons in the queue
 local spd=any_btnq() and 2 or 1
 x=approach(x,x1,spd)
 y=approach(y,y1,spd)

 if x==x1 and y==y1 then
  -- if we've reached goal position, read from queue
  local b=poll_btnq()
  if b then
   local dx,dy=dirx[b],diry[b]
   x1=x+8*dx
   y1=y+8*dy
   if b==0 then flp=true end
   if b==1 then flp=false end
  end
 end
end

function _draw()
 cls()
 spr(0,x,y)
end