Window state notifications. (#104)

samples/SkijaInjectSample/src/main/kotlin/SkijaInjectSample/App.kt

@@ -59,6 +59,10 @@ fun createWindow(title: String) = SwingUtilities.invokeLater {
     val state = State()
     state.text = title
 
+    window.layer.onStateChanged(SkiaLayer.PropertyKind.Renderer) { layer ->
+        println("Changed renderer for $layer: new value is ${layer.renderApi}")
+    }
+
     window.layer.renderer = Renderer(window.layer) {
         renderer, w, h, nanoTime -> displayScene(renderer, w, h, nanoTime, mouseX, mouseY, state)
     }

skiko/src/jvmMain/kotlin/org/jetbrains/skiko/SkiaLayer.kt

@@ -24,6 +24,11 @@ open class SkiaLayer(
     private val properties: SkiaLayerProperties = SkiaLayerProperties()
 ) : JPanel() {
 
+    enum class PropertyKind {
+        Renderer,
+        ContentScale,
+    }
+
     internal val backedLayer : HardwareLayer
 
     init {
@@ -74,8 +79,6 @@ open class SkiaLayer(
         get() = backedLayer.fullscreen
         set(value) { backedLayer.fullscreen = value }
 
-    protected open fun contentScaleChanged() = Unit
-
     var renderer: SkiaRenderer? = null
     val clipComponents = mutableListOf<ClipRectangle>()
 
@@ -84,15 +87,19 @@ open class SkiaLayer(
     internal var redrawer: Redrawer? = null
     private var contextHandler: ContextHandler? = null
     private val fallbackRenderApiQueue = SkikoProperties.fallbackRenderApiQueue.toMutableList()
-    var renderApi: GraphicsApi = fallbackRenderApiQueue[0]
-        private set
+    private var renderApi_ = fallbackRenderApiQueue[0]
+    var renderApi: GraphicsApi
+        get() = renderApi_
+        private set(value) {
+            this.renderApi_ = value
+            notifyChange(PropertyKind.Renderer)
+        }
 
     @Volatile
     private var picture: PictureHolder? = null
     private val pictureRecorder = PictureRecorder()
     private val pictureLock = Any()
 
-
     open fun init() {
         backedLayer.init()
         renderApi = fallbackRenderApiQueue.removeAt(0)
@@ -101,6 +108,19 @@ open class SkiaLayer(
         isInited = true
     }
 
+    private val stateHandlers =
+            mutableMapOf<PropertyKind, MutableList<(SkiaLayer) -> Unit>>()
+
+    fun onStateChanged(kind: PropertyKind, handler: (SkiaLayer) -> Unit) {
+        stateHandlers.getOrPut( kind, { mutableListOf() }) += handler
+    }
+
+    private fun notifyChange(kind: PropertyKind) {
+        stateHandlers.get(kind)?.let { handlers ->
+            handlers.forEach { it(this) }
+        }
+    }
+
     open fun dispose() {
         check(!isDisposed)
         check(isEventDispatchThread())
@@ -129,7 +149,7 @@ open class SkiaLayer(
     override fun paint(g: Graphics) {
         super.paint(g)
         if (backedLayer.checkContentScale()) {
-            contentScaleChanged()
+            notifyChange(PropertyKind.ContentScale)
         }
         redrawer?.syncSize()