WaveView

class WaveView(context: Context, attrs: AttributeSet) : View(context, attrs) {

  private val mAbovePath: Path = Path()
  private val mBelowWavePath: Path = Path()
  private val mAboveWavePaint: Paint = Paint(Paint.ANTI_ALIAS_FLAG)
  private val mBelowWavePaint: Paint = Paint(Paint.ANTI_ALIAS_FLAG)
  private val mDrawFilter: DrawFilter = PaintFlagsDrawFilter(0, Paint.ANTI_ALIAS_FLAG or Paint.FILTER_BITMAP_FLAG)

  private var φ: Float = 0.toFloat()

  init {
    mAboveWavePaint.isAntiAlias = true
    mAboveWavePaint.style = Paint.Style.FILL
    mAboveWavePaint.color = Color.WHITE

    mBelowWavePaint.isAntiAlias = true
    mBelowWavePaint.style = Paint.Style.FILL
    mBelowWavePaint.color = Color.WHITE
    mBelowWavePaint.alpha = 205
  }

  override fun onDraw(canvas: Canvas) {

    canvas.drawFilter = mDrawFilter

    mAbovePath.reset()
    mBelowWavePath.reset()

    φ -= 0.1f

    var y1: Float
    var y2: Float

    val ω = 2 * Math.PI / width

    mAbovePath.moveTo(left.toFloat(), bottom.toFloat())
    mBelowWavePath.moveTo(left.toFloat(), bottom.toFloat())
    var x = 0f
    while (x <= width) {
      /**
       * y=Asin(ωx+φ)+k
       * A—振幅越大，波形在y轴上最大与最小值的差值越大
       * ω—角速度， 控制正弦周期(单位角度内震动的次数)
       * φ—初相，反映在坐标系上则为图像的左右移动。这里通过不断改变φ,达到波浪移动效果
       * k—偏距，反映在坐标系上则为图像的上移或下移。
       */
      y1 = (20 * Math.cos(ω * x + φ) + 20).toFloat()
      y2 = (20 * Math.sin(ω * x + φ) + 20).toFloat()
      mAbovePath.lineTo(x, y1)
      mBelowWavePath.lineTo(x, y2)
      x += 30f
    }
    mAbovePath.lineTo(right.toFloat(), bottom.toFloat())
    mBelowWavePath.lineTo(right.toFloat(), bottom.toFloat())

    canvas.drawPath(mAbovePath, mAboveWavePaint)
    canvas.drawPath(mBelowWavePath, mBelowWavePaint)

    postInvalidateDelayed(40)
  }
}