Triangle View for Android in Kotlin

attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

  <declare-styleable name="TriangleView">
    <attr name="tv_type">
      <enum name="topLeft" value="0" />
      <enum name="topRight" value="1" />
      <enum name="bottomLeft" value="2" />
      <enum name="bottomRight" value="3" />
      <enum name="left" value="4" />
      <enum name="up" value="5" />
      <enum name="right" value="6" />
      <enum name="down" value="7" />
      <enum name="leftNarrow" value="8" />
      <enum name="upNarrow" value="9" />
      <enum name="rightNarrow" value="10" />
      <enum name="downNarrow" value="11" />
    </attr>
    <attr name="tv_color" format="color" />
  </declare-styleable>

</resources>

TriangleView.kt

class TriangleView @JvmOverloads constructor(context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0) : View(context, attrs, defStyleAttr) {
  private val paint by lazy { Paint(Paint.ANTI_ALIAS_FLAG).apply { style = Paint.Style.FILL } }
  private val path: Path = Path()

  @ColorInt
  var color: Int = Color.TRANSPARENT
    set(value) {
      field = value
      invalidate()
    }

  var type: Type = Type.DEFAULT
    set(value) {
      field = value
      invalidate()
    }

  init {
    attrs?.use(context, R.styleable.TriangleView) {
      type = Type.safeOf(getInt(R.styleable.TriangleView_tv_type, Type.DEFAULT.value))
      color = getColor(R.styleable.TriangleView_tv_color, color)
    }
  }

  override fun onDraw(canvas: Canvas) = super.onDraw(canvas).also {
    val widthF = width.toFloat()
    val heightF = height.toFloat()
    when (type) {
      TOP_LEFT -> path.run {
        moveTo(0f, 0f)
        lineTo(0f, heightF)
        lineTo(widthF, 0f)
      }
      TOP_RIGHT -> path.run {
        moveTo(0f, 0f)
        lineTo(widthF, heightF)
        lineTo(widthF, 0f)
      }
      BOTTOM_LEFT -> path.run {
        moveTo(0f, 0f)
        lineTo(0f, heightF)
        lineTo(widthF, heightF)
      }
      BOTTOM_RIGHT -> path.run {
        moveTo(0f, heightF)
        lineTo(widthF, heightF)
        lineTo(widthF, 0f)
      }
      LEFT,
      LEFT_NARROW -> path.run {
        moveTo(widthF, 0f)
        lineTo(widthF.div2ifOrZero(type.isLeftNarrow), heightF.div2())
        lineTo(widthF, heightF)
      }
      UP,
      UP_NARROW -> path.run {
        moveTo(0f, heightF)
        lineTo(widthF.div2(), heightF.div2ifOrZero(type.isUpNarrow))
        lineTo(widthF, heightF)
      }
      RIGHT,
      RIGHT_NARROW -> path.run {
        moveTo(0f, 0f)
        lineTo(widthF.div2if(type.isRightNarrow), heightF.div2())
        lineTo(0f, heightF)
      }
      DOWN,
      DOWN_NARROW -> path.run {
        moveTo(0f, 0f)
        lineTo(widthF.div2(), heightF.div2if(type.isDownNarrow))
        lineTo(widthF, 0f)
      }
    }.also { path.close() }
    canvas.drawPath(path, paint.apply { color = [email protected] })
  }

  enum class Type(val value: Int) {
    TOP_LEFT(0),
    TOP_RIGHT(1),
    BOTTOM_LEFT(2),
    BOTTOM_RIGHT(3),
    LEFT(4),
    UP(5),
    RIGHT(6),
    DOWN(7),
    LEFT_NARROW(8),
    UP_NARROW(9),
    RIGHT_NARROW(10),
    DOWN_NARROW(11);

    companion object {
      val DEFAULT: Type = TOP_LEFT
      fun safeOf(value: Int?): Type = values().firstOrNull { it.value == value } ?: DEFAULT
    }

    val isLeftNarrow: Boolean get() = this == LEFT_NARROW
    val isUpNarrow: Boolean get() = this == UP_NARROW
    val isRightNarrow: Boolean get() = this == RIGHT_NARROW
    val isDownNarrow: Boolean get() = this == DOWN_NARROW
  }
}

inline fun AttributeSet.use(context: Context, @StyleableRes attrs: IntArray, block: TypedArray.() -> Unit) {
  context.obtainStyledAttributes(this, attrs).use { typedArray -> block(typedArray) }
}

private fun Float.div2if(condition: Boolean): Float = if (condition) this.div2() else this
private fun Float.div2ifOrZero(condition: Boolean): Float = if (condition) this.div2() else 0f