Canvas w h = do
  C.save
  C.setSourceRGB 1 1 1
  C.rectangle 0 0 (toDouble w) (toDouble h)
  C.fill >> C.stroke >> C.restore

-- xxx プレゼン時間に応じて波表示
renderWave :: C.Render ()
renderWave = do
  sec <- liftIO elapsedSecFro
clearCanvas :: Int -> Int -> C.Render ()
clearCanvas w h = do
  C.save
  C.setSourceRGB 1 1 1
  C.rectangle 0 0 (toDouble w) (toDouble h)
  C.fill >> C.stroke >> C.restore

-- xxx プレゼン時間に応じて波表示
clearCanvas w h = do
  C.save
  C.setSourceRGB 1 1 1
  C.rectangle 0 0 (toDouble w) (toDouble h)
  C.fill >> C.stroke >> C.restore

-- xxx プレゼン時間に応じて波表示