function param1()
  return "角度", 0, 100, 0
end

function param2()
  return "筆圧透明度", 0, 1, 0
end

function main( x, y, p )

  local w = bs_width() / 2
  if w < 0.25 then
    w = 0.25
  end

  local updateDist = w / 2
  if w > 5 then
    updateDist = w/4
  end
  if w > 20 then
    updateDist = w/10
  end
  if w > 100 then
    updateDist = w/14
  end

  if not firstDraw then
    local distance = bs_distance( lastDrawX - x, lastDrawY - y )
    if distance < updateDist then
      return 0
    end
  end

  local r,g,b = bs_fore()

  local vx,vy = bs_rotate( 1, 0, bs_param1()*3.14159/2/100 )
  vx = vx * w / 2.0
  vy = vy * w / 2.0

  local a = bs_opaque() * 255
  if bs_param2() == 1 then
    a = p * a
  end

  bs_ellipse( x + vx, y + vy, w*sr0,w*sr0, 0, r,g,b, a )
  bs_ellipse( x,y, w*sr1,w*sr1, 0, r,g,b, a )
  bs_ellipse( x - vx, y - vy, w*sr2,w*sr2, 0, r,g,b, a )

  lastDrawX = x
  lastDrawY = y
  firstDraw = false

  return 1
end

bs_setmode( 1 )
lastDrawX = 0
lastDrawY = 0
firstDraw = true

math.randomseed( bs_ms() )
sr0 = 1.0 + 0.2*math.random() - 0.1
sr1 = 1.0 + 0.2*math.random() - 0.1
sr2 = 1.0 + 0.2*math.random() - 0.1