Fix for swing interop on macos. (#269)

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

@@ -118,6 +118,8 @@ fun createWindow(title: String, exitOnClose: Boolean) = SwingUtilities.invokeLat
             window.background = java.awt.Color(0, 0, 0, 0)
         }
         window.layer.transparency = true
+    } else {
+        window.layer.background = java.awt.Color.WHITE
     }
 
     // MANDATORY: set window preferred size before calling pack()

skiko/src/commonMain/kotlin/org/jetbrains/skiko/context/ContextHandler.kt

@@ -9,9 +9,10 @@ import org.jetbrains.skiko.GraphicsApi
 import org.jetbrains.skiko.SkiaLayer
 import org.jetbrains.skiko.hostArch
 import org.jetbrains.skiko.hostOs
+import org.jetbrains.skiko.OS
 
 internal abstract class ContextHandler(val layer: SkiaLayer) {
-    open val clearColor = if (layer.transparency) 0 else -1
+    open val clearColor = if (layer.transparency || hostOs == OS.MacOS) 0 else -1
     var context: DirectContext? = null
     var renderTarget: BackendRenderTarget? = null
     var surface: Surface? = null
@@ -21,7 +22,7 @@ internal abstract class ContextHandler(val layer: SkiaLayer) {
     abstract fun initCanvas()
 
     fun clearCanvas() {
-        val color = if (layer.fullscreen) -1 else clearColor
+        val color = if (layer.fullscreen && hostOs != OS.MacOS) -1 else clearColor
         canvas?.clear(color)
     }