Proper clipping of SwingPanel interop

compose/ui/ui/api/desktop/ui.api

@@ -3120,7 +3120,6 @@ public abstract interface class androidx/compose/ui/platform/PlatformContext {
 	public fun isWindowTransparent ()Z
 	public fun requestFocus ()Z
 	public fun setPointerIcon (Landroidx/compose/ui/input/pointer/PointerIcon;)V
-	public fun setWindowTransparent (Z)V
 }
 
 public final class androidx/compose/ui/platform/PlatformContext$Companion {

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/awt/ComposeBridge.desktop.kt

@@ -67,13 +67,14 @@ internal abstract class ComposeBridge(
     private var isDisposed = false
 
     private val _invisibleComponent = InvisibleComponent()
-
-    abstract val component: JComponent
     val invisibleComponent: Component get() = _invisibleComponent
 
+    abstract val component: JComponent
     abstract val renderApi: GraphicsApi
 
+    abstract val interopBlendingSupported: Boolean
     abstract val clipComponents: MutableList<ClipRectangle>
+    private val clipMap = mutableMapOf<Component, ClipComponent>()
 
     // Needed for case when componentLayer is a wrapper for another Component that need to acquire focus events
     // e.g. canvas in case of ComposeWindowLayer
@@ -149,6 +150,7 @@ internal abstract class ComposeBridge(
     private val desktopTextInputService = DesktopTextInputService(platformComponent)
     protected val platformContext = DesktopPlatformContext()
     internal var rootForTestListener: PlatformContext.RootForTestListener? by DelegateRootForTestListener()
+    internal var isWindowTransparent by platformContext::isWindowTransparent
 
     private val semanticsOwnerListener = DesktopSemanticsOwnerListener()
     val sceneAccessible = ComposeSceneAccessible {
@@ -337,6 +339,18 @@ internal abstract class ComposeBridge(
         initContent()
     }
 
+    fun addClipComponent(component: Component) {
+        val clipComponent = ClipComponent(component)
+        clipMap[component] = clipComponent
+        clipComponents.add(clipComponent)
+    }
+
+    fun removeClipComponent(component: Component) {
+        clipMap.remove(component)?.let {
+            clipComponents.remove(it)
+        }
+    }
+
     private var _initContent: (() -> Unit)? = null
 
     protected fun initContent() {

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/awt/ComposeDialog.desktop.kt

@@ -245,9 +245,9 @@ class ComposeDialog : JDialog {
      * `true`, otherwise AWT will throw an exception.
      */
     var isTransparent: Boolean
-        get() = delegate.isTransparent
+        get() = delegate.isWindowTransparent
         set(value) {
-            delegate.isTransparent = value
+            delegate.isWindowTransparent = value
         }
 
     /**

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/awt/ComposePanel.desktop.kt

@@ -34,7 +34,9 @@ import javax.swing.JLayeredPane
 import javax.swing.SwingUtilities.isEventDispatchThread
 import org.jetbrains.skiko.ClipComponent
 import org.jetbrains.skiko.GraphicsApi
+import org.jetbrains.skiko.OS
 import org.jetbrains.skiko.SkiaLayerAnalytics
+import org.jetbrains.skiko.hostOs
 
 /**
  * ComposePanel is a panel for building UI using Compose for Desktop.
@@ -86,7 +88,6 @@ class ComposePanel @ExperimentalComposeUiApi constructor(
     private var _isFocusable = true
     private var _isRequestFocusEnabled = false
     private var bridge: ComposeBridge? = null
-    private val clipMap = mutableMapOf<Component, ClipComponent>()
     private var content: (@Composable () -> Unit)? = null
 
     /**
@@ -171,38 +172,58 @@ class ComposePanel @ExperimentalComposeUiApi constructor(
     }
 
     override fun add(component: Component): Component {
-        if (bridge == null) {
-            return component
+        addToLayer(component, componentLayer)
+        if (!interopBlending) {
+            bridge?.addClipComponent(component)
         }
-        val clipComponent = ClipComponent(component)
-        clipMap[component] = clipComponent
-        bridge!!.clipComponents.add(clipComponent)
-        return super.add(component, Integer.valueOf(0))
+        return component
     }
 
     override fun remove(component: Component) {
-        bridge!!.clipComponents.remove(clipMap[component]!!)
-        clipMap.remove(component)
+        bridge?.removeClipComponent(component)
         super.remove(component)
     }
 
+    private fun addToLayer(component: Component, layer: Int) {
+        if (renderApi == GraphicsApi.METAL && bridge !is SwingComposeBridge) {
+            // Applying layer on macOS makes our bridge non-transparent
+            // But it draws always on top, so we can just add it as-is
+            // TODO: Figure out why it makes difference in transparency
+            super.add(component, 0)
+        } else {
+            super.setLayer(component, layer)
+            super.add(component)
+        }
+    }
+
+    private val bridgeLayer: Int = 10
+    private val componentLayer: Int
+        get() = if (interopBlending) 0 else 20
+
+    private val renderOnGraphics: Boolean
+        get() = System.getProperty("compose.swing.render.on.graphics").toBoolean()
+    private val _interopBlending: Boolean
+        get() = System.getProperty("compose.interop.blending").toBoolean()
+    private val interopBlending: Boolean
+        get() = _interopBlending &&
+            (renderOnGraphics || requireNotNull(bridge).interopBlendingSupported)
+
     override fun addNotify() {
         super.addNotify()
 
         // After [super.addNotify] is called we can safely initialize the bridge and composable
         // content.
-        if (bridge == null) {
-            bridge = createComposeBridge()
+        if (this.bridge == null) {
+            val bridge = createComposeBridge()
+            this.bridge = bridge
             initContent()
-            super.add(bridge!!.invisibleComponent, Integer.valueOf(1))
-            super.add(bridge!!.component, Integer.valueOf(1))
+            addToLayer(bridge.invisibleComponent, bridgeLayer)
+            addToLayer(bridge.component, bridgeLayer)
         }
     }
 
     private fun createComposeBridge(): ComposeBridge {
-        val renderOnGraphics = System.getProperty("compose.swing.render.on.graphics").toBoolean()
         val bridge: ComposeBridge = if (renderOnGraphics) {
-            // TODO: Add window transparent info
             SwingComposeBridge(skiaLayerAnalytics, layoutDirectionFor(this))
         } else {
             WindowComposeBridge(skiaLayerAnalytics, layoutDirectionFor(this))
@@ -328,5 +349,5 @@ class ComposePanel @ExperimentalComposeUiApi constructor(
      * environment variable.
      */
     val renderApi: GraphicsApi
-        get() = if (bridge != null) bridge!!.renderApi else GraphicsApi.UNKNOWN
+        get() = bridge?.renderApi ?: GraphicsApi.UNKNOWN
 }

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/awt/ComposeWindow.desktop.kt

@@ -183,7 +183,7 @@ class ComposeWindow @ExperimentalComposeUiApi constructor(
      * Transparency should be set only if window is not showing and `isUndecorated` is set to
      * `true`, otherwise AWT will throw an exception.
      */
-    var isTransparent: Boolean by delegate::isTransparent
+    var isTransparent: Boolean by delegate::isWindowTransparent
 
     var placement: WindowPlacement
         get() = when {

compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/awt/ComposeWindowDelegate.desktop.kt

@@ -60,30 +60,123 @@ internal class ComposeWindowDelegate(
         }
     internal val scene: ComposeScene
         get() = bridge.scene
+
     internal val windowAccessible: Accessible
         get() = bridge.sceneAccessible
+
     internal var rootForTestListener by bridge::rootForTestListener
+
     val undecoratedWindowResizer = UndecoratedWindowResizer(window)
 
+    var fullscreen: Boolean
+        get() = bridge.component.fullscreen
+        set(value) {
+            bridge.component.fullscreen = value
+        }
+
+    var compositionLocalContext: CompositionLocalContext?
+        get() = bridge.compositionLocalContext
+        set(value) {
+            bridge.compositionLocalContext = value
+        }
+
+    @ExperimentalComposeUiApi
+    var exceptionHandler: WindowExceptionHandler?
+        get() = bridge.exceptionHandler
+        set(value) {
+            bridge.exceptionHandler = value
+        }
+
+    val windowHandle: Long
+        get() = bridge.component.windowHandle
+
+    val renderApi: GraphicsApi
+        get() = bridge.renderApi
+
+    private val _interopBlending: Boolean
+        get() = System.getProperty("compose.interop.blending").toBoolean()
+    private val interopBlending: Boolean
+        get() = _interopBlending && bridge.interopBlendingSupported
+
+    var isWindowTransparent: Boolean = false
+        set(value) {
+            if (field != value) {
+                check(isUndecorated()) { "Transparent window should be undecorated!" }
+                check(!window.isDisplayable) {
+                    "Cannot change transparency if window is already displayable."
+                }
+                field = value
+                bridge.isWindowTransparent = value
+                bridge.transparency = value || interopBlending
+
+                /*
+                 * Windows makes clicks on transparent pixels fall through, but it doesn't work
+                 * with GPU accelerated rendering since this check requires having access to pixels from CPU.
+                 *
+                 * JVM doesn't allow override this behaviour with low-level windows methods, so hack this in this way.
+                 * Based on tests, it doesn't affect resulting pixel color.
+                 *
+                 * Note: Do not set isOpaque = false for this container
+                 */
+                if (value && hostOs == OS.Windows) {
+                    pane.background = Color(0, 0, 0, 1)
+                    pane.isOpaque = true
+                } else {
+                    pane.background = null
+                    pane.isOpaque = false
+                }
+
+                window.background = if (value && !skikoTransparentWindowHack) Color(0, 0, 0, 0) else null
+            }
+        }
+
+    /**
+     * There is a hack inside skiko OpenGL and Software redrawers for Windows that makes current
+     * window transparent without setting `background` to JDK's window. It's done by getting native
+     * component parent and calling `DwmEnableBlurBehindWindow`.
+     *
+     * FIXME: Make OpenGL work inside transparent window (background == Color(0, 0, 0, 0)) without this hack.
+     *
+     * See `enableTransparentWindow` (skiko/src/awtMain/cpp/windows/window_util.cc)
+     */
+    private val skikoTransparentWindowHack: Boolean
+        get() = hostOs == OS.Windows && renderApi != GraphicsApi.DIRECT3D
+
     private val _pane = object : JLayeredPane() {
         override fun setBounds(x: Int, y: Int, width: Int, height: Int) {
-            bridge.component.setSize(width, height)
+            bridge.component.setBounds(0, 0, width, height)
             super.setBounds(x, y, width, height)
         }
 
         override fun add(component: Component): Component {
-            val clipComponent = ClipComponent(component)
-            clipMap[component] = clipComponent
-            bridge.clipComponents.add(clipComponent)
-            return add(component, Integer.valueOf(0))
+            addToLayer(component, componentLayer)
+            if (!interopBlending) {
+                bridge.addClipComponent(component)
+            }
+            return component
         }
 
         override fun remove(component: Component) {
-            bridge.clipComponents.remove(clipMap[component]!!)
-            clipMap.remove(component)
+            bridge.removeClipComponent(component)
             super.remove(component)
         }
 
+        private fun addToLayer(component: Component, layer: Int) {
+            if (renderApi == GraphicsApi.METAL) {
+                // Applying layer on macOS makes our bridge non-transparent
+                // But it draws always on top, so we can just add it as-is
+                // TODO: Figure out why it makes difference in transparency
+                super.add(component, 0)
+            } else {
+                super.setLayer(component, layer)
+                super.add(component)
+            }
+        }
+
+        private val bridgeLayer: Int get() = 10
+        private val componentLayer: Int
+            get() = if (interopBlending) 0 else 20
+
         override fun addNotify() {
             super.addNotify()
             bridge.component.requestFocus()
@@ -94,8 +187,8 @@ internal class ComposeWindowDelegate(
 
         init {
             layout = null
-            super.add(bridge.invisibleComponent, 1)
-            super.add(bridge.component, 1)
+            addToLayer(bridge.invisibleComponent, bridgeLayer)
+            addToLayer(bridge.component, bridgeLayer)
         }
 
         fun dispose() {
@@ -106,8 +199,6 @@ internal class ComposeWindowDelegate(
 
     val pane get() = _pane
 
-    private val clipMap = mutableMapOf<Component, ClipComponent>()
-
     init {
         pane.focusTraversalPolicy = object : FocusTraversalPolicy() {
             override fun getComponentAfter(aContainer: Container?, aComponent: Component?) = null
@@ -117,6 +208,7 @@ internal class ComposeWindowDelegate(
             override fun getDefaultComponent(aContainer: Container?) = null
         }
         pane.isFocusCycleRoot = true
+        bridge.transparency = interopBlending
         setContent {}
     }
 
@@ -128,18 +220,6 @@ internal class ComposeWindowDelegate(
         _pane.remove(component)
     }
 
-    var fullscreen: Boolean
-        get() = bridge.component.fullscreen
-        set(value) {
-            bridge.component.fullscreen = value
-        }
-
-    var compositionLocalContext: CompositionLocalContext?
-        get() = bridge.compositionLocalContext
-        set(value) {
-            bridge.compositionLocalContext = value
-        }
-
     fun setContent(
         onPreviewKeyEvent: (KeyEvent) -> Boolean = { false },
         onKeyEvent: (KeyEvent) -> Boolean = { false },
@@ -225,38 +305,6 @@ internal class ComposeWindowDelegate(
         }
     }
 
-    @ExperimentalComposeUiApi
-    var exceptionHandler: WindowExceptionHandler?
-        get() = bridge.exceptionHandler
-        set(value) {
-            bridge.exceptionHandler = value
-        }
-
-    val windowHandle: Long
-        get() = bridge.component.windowHandle
-
-    val renderApi: GraphicsApi
-        get() = bridge.renderApi
-
-    var isTransparent: Boolean
-        get() = bridge.transparency
-        set(value) {
-            if (value != bridge.transparency) {
-                check(isUndecorated()) { "Transparent window should be undecorated!" }
-                check(!window.isDisplayable) {
-                    "Cannot change transparency if window is already displayable."
-                }
-                bridge.transparency = value
-                if (value) {
-                    if (hostOs != OS.Windows) {
-                        window.background = Color(0, 0, 0, 0)
-                    }
-                } else {
-                    window.background = null
-                }
-            }
-        }
-
     fun addMouseListener(listener: MouseListener) {
         bridge.component.addMouseListener(listener)
     }