F = {
  -- two charts; one fine-grained and one coarse-grained
  data1={},  -- fine-grained samples: memory footprint size
  data2={}, -- coarse-grained samples: each is mean of X fine-grained samples
  N1 = 300,  -- # of fine-grained samples to show
  N2 = 300,  -- # of coarse-grained samples to show
  X = 10,  -- number of fine-grained samples that make up one coarse-grained sample; must be <= N1
  previous_sample=0,  -- time at which we took previous fine-grained sample
  nsamples=0,  -- running count of fine-grained samples taken since previous coarse-grained sample
}

function update_footprint()
  if Current_time-F.previous_sample < 1 then
    return
  end
  F.previous_sample = Current_time
  assert(#F.data1 <= F.N1)
  if #F.data1 == F.N1 then
    table.remove(F.data1, 1)
  end
  table.insert(F.data1, collectgarbage('count'))
  F.nsamples = F.nsamples+1
  -- if we ever have an error in data collection we quickly lose it because this triggers
  --assert(F.nsamples <= F.X)
  -- don't trust nsamples beyond this point
  if F.nsamples < F.X then
    return
  end
  assert(#F.data2 <= F.N2)
  if #F.data2 == F.N2 then
    table.remove(F.data2, 1)
  end
  table.insert(F.data2, mean(F.data1, #F.data1-F.X+1, #F.data1))
  F.nsamples = 0
end

function draw_debug()
  if not Display_settings.show_debug then return end
  App.color{r=1,g=1,b=1}
  love.graphics.rectangle('fill', App.screen.width-900,App.screen.height-460, 900,460)
  App.color{r=0.6,g=0.6,b=0.6}
  love.graphics.rectangle('line', App.screen.width-895,App.screen.height-455, 890,450)
  App.color{r=0,g=0,b=0}
  draw_graph(F.data1, 'fast', App.screen.width-820,App.screen.height-445, 800,200, F.N1)
  draw_graph(F.data2, 'slow', App.screen.width-820,App.screen.height-235, 800,200, F.N2)
end

function draw_graph(data, title, x,y, w,h, n)
  love.graphics.line(x,y, x,y+h)
  love.graphics.line(x,y+h, x+w,y+h)
  love.graphics.print(title, x+w/2,y+h+5)
  if #data == 0 then return end
  local dx = w/n
  local maxy = max(data)
  maxy = math.floor(maxy*1.1/100)*100
  love.graphics.print(tostring(maxy), x-70, y)
  for i,val in ipairs(data) do
    local xx = x + (i-1)*dx
    local yy = y + (1 - val/maxy)*h
    love.graphics.circle('fill', xx,yy, 2)
  end
end

function sum(arr, lo, hi)
  local result = 0
  for i=lo,hi do
    result = result + arr[i]
  end
  return result
end

function mean(arr, lo, hi)
  return sum(arr, lo, hi)/(hi-lo+1)
end

function max(arr)
  if #arr == 0 then return end
  local result = arr[1]
  for _,v in ipairs(arr) do
    if v > result then
      result = v
    end
  end
  assert(result)
  return result
end