ScannerOverlay.kt

package com.bakawaii.roomex

import android.content.Context
import android.graphics.*
import android.util.AttributeSet
import android.view.View

/**
 * Created by Bakawaii on 2017/12/11.
 */
class ScannerOverlay @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0) : View(context, attrs, defStyleAttr) {

    private val paint: Paint = Paint().apply {
        color = Color.RED
        style = Paint.Style.FILL_AND_STROKE
        strokeWidth = 20F
        isAntiAlias = true
        strokeCap = Paint.Cap.ROUND
        strokeJoin = Paint.Join.ROUND
    }

    private val path: Path = Path()

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)

        val lengthRefs = if (measuredHeight > measuredWidth) measuredWidth else measuredHeight
        val strokeWidth = lengthRefs.toFloat() / 25
        val strokeLength = lengthRefs.toFloat() / 5

        paint.strokeWidth = strokeWidth

        val offset = strokeWidth / 2

        path.reset()
        //Top-left
        path.moveTo(0F + offset, 0F + offset + strokeLength)
        path.lineTo(0F + offset, 0F + offset)
        path.moveTo(0F + offset, 0F + offset)
        path.lineTo(0F + offset + strokeLength, 0F + offset)

        //Top-right
        path.moveTo(measuredWidth.toFloat() - offset, strokeLength + offset)
        path.lineTo(measuredWidth.toFloat() - offset, 0F + offset)
        path.moveTo(measuredWidth.toFloat() - offset, 0F + offset)
        path.lineTo(measuredWidth.toFloat() - offset - strokeLength, 0F + offset)

        //Bottom-left
        path.moveTo(0F + offset, measuredHeight - offset - strokeLength)
        path.lineTo(0F + offset, measuredHeight - offset)
        path.moveTo(0F + offset, measuredHeight - offset)
        path.lineTo(0F + offset + strokeLength, measuredHeight - offset)

        //Bottom-right
        path.moveTo(measuredWidth.toFloat() - offset, measuredHeight - offset - strokeLength)
        path.lineTo(measuredWidth.toFloat() - offset, measuredHeight - offset)
        path.moveTo(measuredWidth.toFloat() - offset, measuredHeight - offset)
        path.lineTo(measuredWidth.toFloat() - strokeLength, measuredHeight - offset)
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        canvas.drawPath(path, paint)
    }
}