Calculating next frame

DynamicView.kt

class DynamicView
@JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0
) : View(context, attrs, defStyleAttr) {

    private var lastUpdateTime: Long = System.currentTimeMillis()
    // ..

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)

        val delta = System.currentTimeMillis() - lastUpdateTime
        calculateNextFrame(delta)

        val radius = minRadius + (maxRadius - minRadius) * amplitude / MAX_AMPLITUDE
        canvas.drawCircle(width / 2f, height / 2f, radius, paint)

        lastUpdateTime = System.currentTimeMillis()
        invalidate()
    }

    private fun calculateNextFrame(dt: Long) {
        if (animateToAmplitude != amplitude) {
            amplitude += deltaAmplitude * dt
            if (deltaAmplitude > 0) {
                amplitude = amplitude.coerceAtMost(animateToAmplitude)
            } else {
                amplitude = amplitude.coerceAtLeast(animateToAmplitude)
            }
        }
    }

    fun setAmplitude(value: Float) {
        //..
    }

    private companion object {

        private const val MAX_AMPLITUDE = 1200f
    }
}