Cacao: Fix changing button backgrounds after adding button to superview

src/main/kotlin/net/shadowfacts/cacao/view/button/AbstractButton.kt

@@ -46,18 +46,33 @@ abstract class AbstractButton<Impl: AbstractButton<Impl>>(val content: View, val
 	 * unless the background view is not fully opaque.
 	 */
 	var background: View? = NinePatchView(NinePatchTexture.BUTTON_BG)
+		set(value) {
+			field?.removeFromSuperview()
+			field = value
+			value?.also(::addBackground)
+		}
 	/**
 	 * The background to draw when the button is hovered over by the mouse.
 	 * If `null`, the normal [background] will be used.
 	 * @see background
 	 */
 	var hoveredBackground: View? = NinePatchView(NinePatchTexture.BUTTON_HOVERED_BG)
+		set(value) {
+			field?.removeFromSuperview()
+			field = value
+			value?.also(::addBackground)
+		}
 	/**
 	 * The background to draw when the button is [disabled].
 	 * If `null`, the normal [background] will be used.
 	 * @see background
 	 */
 	var disabledBackground: View? = NinePatchView(NinePatchTexture.BUTTON_DISABLED_BG)
+		set(value) {
+			field?.removeFromSuperview()
+			field = value
+			value?.also(::addBackground)
+		}
 
 	/**
 	 * The tooltip text shown when this button is hovered.
@@ -74,19 +89,25 @@ abstract class AbstractButton<Impl: AbstractButton<Impl>>(val content: View, val
 			content.rightAnchor.greaterThanOrEqualTo(rightAnchor - padding, WEAK)
 			content.topAnchor.lessThanOrEqualTo(topAnchor + padding, WEAK)
 			content.bottomAnchor.greaterThanOrEqualTo(bottomAnchor - padding, WEAK)
-
-			listOfNotNull(background, hoveredBackground, disabledBackground).forEach {
-				addSubview(it)
-				it.leftAnchor equalTo leftAnchor
-				it.rightAnchor equalTo rightAnchor
-				it.topAnchor equalTo topAnchor
-				it.bottomAnchor equalTo bottomAnchor
-			}
 		}
 
+		listOfNotNull(background, hoveredBackground, disabledBackground).forEach(::addBackground)
+
 		super.wasAdded()
 	}
 
+	private fun addBackground(view: View) {
+		if (superview != null && hasSolver) {
+			addSubview(view)
+			solver.dsl {
+				view.leftAnchor equalTo leftAnchor
+				view.rightAnchor equalTo rightAnchor
+				view.topAnchor equalTo topAnchor
+				view.bottomAnchor equalTo bottomAnchor
+			}
+		}
+	}
+
 	override fun draw(matrixStack: MatrixStack, mouse: Point, delta: Float) {
 		RenderHelper.pushMatrix()
 		RenderHelper.translate(floor(frame.left), floor(frame.top))