RulerView.kt

class RulerView @JvmOverloads constructor(ctx: Context, attrs: AttributeSet? = null) : View(ctx, attrs), AnkoLogger {

    private var centimeters: Int = 0
    private var cmSize = 0f

    private val lPaint = Paint()
    private val tPaint = TextPaint()

    companion object {

        private const val LINE_WIDTH = 2f
        private const val RULER_COLOR = Color.BLACK
    }

    init {
        val pAlpha = 40
        tPaint.apply {
            isAntiAlias = true
            style = Paint.Style.FILL
            textSize = 14f
            color = RULER_COLOR
            alpha = pAlpha
        }

        lPaint.apply {
            isAntiAlias = true
            style = Paint.Style.STROKE
            strokeWidth = LINE_WIDTH
            color = RULER_COLOR
            alpha = pAlpha
        }
    }

    fun init(width: Int) {
        centimeters = width / 10
    }

    override fun onSizeChanged(width: Int, height: Int, oldw: Int, oldh: Int) {
        super.onSizeChanged(width, height, oldw, oldh)
        cmSize = width.toFloat() / centimeters
    }

    override fun onDraw(canvas: Canvas?) {
//        ifDebug { info { "::: @onDraw -> width = $width cmSize = $cmSize" } }

        for (i in 0..centimeters) {
            var offset = 0f
            var lHeight: Float
            var label: String? = null
            when {
                i == 0 -> {
                    lHeight = height * 0.65f
                    offset = LINE_WIDTH / 2
                }
                i % 10 == 0 -> {
                    lHeight = height * 0.6f
                    label = i.toString()
                }
                i % 5 == 0 && i % 10 != 0 -> {
                    lHeight = height * 0.45f
                }
                else -> {
                    lHeight = height * 0.25f
                }
            }
            if (i > 0 && i % centimeters == 0) offset = LINE_WIDTH / -2f

            val lX = (i * cmSize) + offset
//            ifDebug { info { "::: @onDraw -> lX = $lX" } }
            canvas?.drawLine(lX, 0f, lX, lHeight, lPaint)

            label?.let {
                val tWidth = tPaint.measureText(it)
                val tX = lX - tWidth / 2
                canvas?.drawText(it, tX, height.toFloat() - 2, tPaint)
            }
        }
    }

}