CircularLayout.kt

package com.bfreq.dice.widget

import android.content.Context
import android.util.AttributeSet
import android.view.View
import android.view.ViewGroup
import com.bfreq.dice.R
import com.bfreq.dice.util.forEachChild
import com.bfreq.dice.util.forEachChildIndexed

/**
 * All children of this class will be laid out in a circle.
 * This assumes all children are square.
 * There is no visibility support as of now.
 */
class CircularLayout : ViewGroup {

    private val outerCircularPadding = resources.getDimensionPixelSize(R.dimen.circular_padding)
    private val startingRadianOffset = -(2 * Math.PI / 4) // rotates to noon.

    constructor(context: Context?) : super(context)
    constructor(context: Context?, attrs: AttributeSet?) : super(context, attrs)
    constructor(context: Context?, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr)
    constructor(context: Context?, attrs: AttributeSet?, defStyleAttr: Int, defStyleRes: Int) : super(context, attrs, defStyleAttr, defStyleRes)

    /**
     * This makes sure that no view is at the 12 o'clock position.
     * Changing this value will request a layout.
     */
    var isAdjustingOffNoon = false
        set(value) {
            field = value
            requestLayout()
        }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec)
        forEachChild { measureChild(it, widthMeasureSpec, heightMeasureSpec) }
    }

    override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
        val radianPerChild = 2 * Math.PI / childCount
        val adjustOffNoon: Double = if (isAdjustingOffNoon) radianPerChild / 2 else 0.0

        val cx = width / 2
        val cy = height / 2
        forEachChildIndexed {
            index, child ->

            val radian = radianPerChild * index + startingRadianOffset + adjustOffNoon
            layoutChild(radian, cx, cy, child)
        }
    }

    fun layoutChild(radian: Double, parentCenterX: Int, parentCenterY: Int, child: View) {
        val radius = width / 2 - (child.measuredWidth / 2 + outerCircularPadding)
        val childCenterX = parentCenterX + radius * Math.cos(radian)
        val childCenterY = parentCenterY + radius * Math.sin(radian)

        child.layout(
                (childCenterX - child.measuredWidth / 2).toInt(),
                (childCenterY - child.measuredHeight / 2).toInt(),
                (childCenterX + child.measuredWidth / 2).toInt(),
                (childCenterY + child.measuredHeight / 2).toInt()
        )
    }
}