Update the NinePatchView computed regions on layout changes

Otherwise, updating the size of a button (e.g. by changing it's content)
would result in the button having an incorrectly displayed background

src/main/kotlin/net/shadowfacts/cacao/util/properties/ObservableLateInitProperty.kt

@@ -9,6 +9,9 @@ class ObservableLateInitProperty<T: Any>(val observer: (T) -> Unit) {
 
 	lateinit var storage: T
 
+	val isInitialized: Boolean
+		get() = this::storage.isInitialized
+
 	operator fun getValue(thisRef: Any, property: KProperty<*>): T {
 		return storage
 	}

src/main/kotlin/net/shadowfacts/cacao/util/properties/ResettableLazyProperty.kt

@@ -0,0 +1,21 @@
+package net.shadowfacts.cacao.util
+
+import kotlin.reflect.KProperty
+
+/**
+ * @author shadowfacts
+ */
+class ResettableLazyProperty<Value>(val initializer: () -> Value) {
+	var value: Value? = null
+
+	operator fun getValue(thisRef: Any, property: KProperty<*>): Value {
+		if (value == null) {
+			value = initializer()
+		}
+		return value!!
+	}
+
+	fun reset() {
+		value = null
+	}
+}

src/main/kotlin/net/shadowfacts/cacao/view/NinePatchView.kt

@@ -4,6 +4,7 @@ import net.shadowfacts.cacao.geometry.Point
 import net.shadowfacts.cacao.geometry.Rect
 import net.shadowfacts.cacao.util.NinePatchTexture
 import net.shadowfacts.cacao.util.RenderHelper
+import net.shadowfacts.cacao.util.ResettableLazyProperty
 
 /**
  * A helper class for drawing a [NinePatchTexture] in a view.
@@ -15,37 +16,62 @@ import net.shadowfacts.cacao.util.RenderHelper
 class NinePatchView(val ninePatch: NinePatchTexture): View() {
 
 	// Corners
-	private val topLeft: Rect by lazy {
+	protected val `$topLeft` = ResettableLazyProperty {
 		Rect(0.0, 0.0, ninePatch.cornerWidth.toDouble(), ninePatch.cornerHeight.toDouble())
 	}
-	private val topRight by lazy {
+	protected val topLeft by `$topLeft`
+
+	protected val `$topRight` = ResettableLazyProperty {
 		Rect(bounds.width - ninePatch.cornerWidth, 0.0, ninePatch.cornerWidth.toDouble(), ninePatch.cornerHeight.toDouble())
 	}
-	private val bottomLeft by lazy {
+	protected val topRight by `$topRight`
+
+	protected val `$bottomLeft` = ResettableLazyProperty {
 		Rect(0.0, bounds.height - ninePatch.cornerHeight, ninePatch.cornerWidth.toDouble(), ninePatch.cornerHeight.toDouble())
 	}
-	private val bottomRight by lazy {
+	protected val bottomLeft by `$bottomLeft`
+
+	protected val `$bottomRight` = ResettableLazyProperty {
 		Rect(bounds.width - ninePatch.cornerWidth, bounds.height - ninePatch.cornerHeight, ninePatch.cornerWidth.toDouble(), ninePatch.cornerHeight.toDouble())
 	}
+	protected val bottomRight by `$bottomRight`
+
 
 	// Edges
-	private val topMiddle by lazy {
+	protected val `$topMiddle` = ResettableLazyProperty {
 		Rect(ninePatch.cornerWidth.toDouble(), topLeft.top, bounds.width - 2 * ninePatch.cornerWidth, ninePatch.cornerHeight.toDouble())
 	}
-	private val bottomMiddle by lazy {
+	protected val topMiddle by `$topMiddle`
+
+	protected val `$bottomMiddle` = ResettableLazyProperty {
 		Rect(topMiddle.left, bottomLeft.top, topMiddle.width, topMiddle.height)
 	}
-	private val leftMiddle by lazy {
+	protected val bottomMiddle by `$bottomMiddle`
+
+	protected val `$leftMiddle` = ResettableLazyProperty {
 		Rect(topLeft.left, ninePatch.cornerHeight.toDouble(), ninePatch.cornerWidth.toDouble(), bounds.height - 2 * ninePatch.cornerHeight)
 	}
-	private val rightMiddle by lazy {
+	protected val leftMiddle by `$leftMiddle`
+
+	protected val `$rightMiddle` = ResettableLazyProperty {
 		Rect(topRight.left, leftMiddle.top, leftMiddle.width, leftMiddle.height)
 	}
+	protected val rightMiddle by `$rightMiddle`
+
 
 	// Center
-	private val center by lazy {
+	protected val `$center` = ResettableLazyProperty {
 		Rect(topLeft.right, topLeft.bottom, topMiddle.width, leftMiddle.height)
 	}
+	protected val center by `$center`
+
+	protected val delegates = listOf(`$topLeft`, `$topRight`, `$bottomLeft`, `$bottomRight`, `$topMiddle`, `$bottomMiddle`, `$leftMiddle`, `$rightMiddle`, `$center`)
+
+	override fun didLayout() {
+		super.didLayout()
+
+		delegates.forEach(ResettableLazyProperty<Rect>::reset)
+	}
 
 	override fun drawContent(mouse: Point, delta: Float) {
 		drawCorners()