ClickDrawable.kt

class ClickDrawable(layers: Array<out Drawable> = arrayOf()) : LayerDrawable(layers) {

    …
    private val mask: Drawable =
        ColorDrawable(0xFF00FFFF.toInt()).apply { alpha = 0 }

    init {
        addLayer(mask)
    }
    …

    @Keep
    private fun setMaskAlpha(alpha: Int) {
        mask.alpha = alpha
        invalidateSelf()
    }

    private fun colorMask(fromAlpha: Int, toAlpha: Int) {
        val anim = ObjectAnimator.ofInt(this, "maskAlpha", fromAlpha, toAlpha, fromAlpha)
        anim.duration = DURATION
        anim.interpolator = LinearInterpolator()
        anim.start()
    }

    private fun setClickActive(active: Boolean) {
        if (mActive != active) {
            mActive = active
            if (active && canStart) {
                …
                colorMask(0, 64)
            }
        }
    }

    @Keep
    private fun setBounds(value: Float) { … }
    …

    private companion object { 
        const val DURATION = 225L
    }
}