Add ability to change opacity for compose view

compose/ui/ui/src/uikitMain/kotlin/androidx/compose/ui/scene/UIViewComposeSceneLayer.uikit.kt

@@ -97,10 +97,9 @@ internal class UIViewComposeSceneLayer(
     }
 
     private fun createSkikoUIView(renderDelegate: RenderingUIView.Delegate): RenderingUIView =
-        RenderingUIView(
-            renderDelegate = renderDelegate,
-            transparency = true,
-        )
+        RenderingUIView(renderDelegate = renderDelegate).apply {
+            opaque = false
+        }
 
     private fun createComposeScene(
         invalidate: () -> Unit,

compose/ui/ui/src/uikitMain/kotlin/androidx/compose/ui/uikit/ComposeUIViewControllerConfiguration.uikit.kt

@@ -35,6 +35,13 @@ class ComposeUIViewControllerConfiguration {
 
     @ExperimentalComposeApi
     var platformLayers: Boolean = true
+
+    /**
+     * Determines whether the Compose view should have an opaque background.
+     * Warning: disabling opaque layer may affect performance.
+     */
+    @ExperimentalComposeApi
+    var opaque: Boolean = true
 }
 
 /**

compose/ui/ui/src/uikitMain/kotlin/androidx/compose/ui/window/ComposeContainer.uikit.kt

@@ -146,10 +146,12 @@ internal class ComposeContainer(
         }
     }
 
+    @OptIn(ExperimentalComposeApi::class)
     override fun loadView() {
         view = UIView().apply {
-            backgroundColor = UIColor.whiteColor
             setClipsToBounds(true)
+            opaque = configuration.opaque
+            backgroundColor = if (configuration.opaque) UIColor.whiteColor else UIColor.clearColor
         } // rootView needs to interop with UIKit
     }
 
@@ -273,11 +275,11 @@ internal class ComposeContainer(
     fun createComposeSceneContext(platformContext: PlatformContext): ComposeSceneContext =
         ComposeSceneContextImpl(platformContext)
 
+    @OptIn(ExperimentalComposeApi::class)
     private fun createSkikoUIView(renderRelegate: RenderingUIView.Delegate): RenderingUIView =
-        RenderingUIView(
-            renderDelegate = renderRelegate,
-            transparency = false,
-        )
+        RenderingUIView(renderDelegate = renderRelegate).apply {
+            opaque = configuration.opaque
+        }
 
     @OptIn(ExperimentalComposeApi::class)
     private fun createComposeScene(

compose/ui/ui/src/uikitMain/kotlin/androidx/compose/ui/window/MetalRedrawer.uikit.kt

@@ -190,8 +190,7 @@ internal class InflightCommandBuffers(
 
 internal class MetalRedrawer(
     private val metalLayer: CAMetalLayer,
-    private val callbacks: MetalRedrawerCallbacks,
-    private val transparency: Boolean,
+    private val callbacks: MetalRedrawerCallbacks
 ) {
     // Workaround for KN compiler bug
     // Type mismatch: inferred type is objcnames.protocols.MTLDeviceProtocol but platform.Metal.MTLDeviceProtocol was expected
@@ -228,6 +227,13 @@ internal class MetalRedrawer(
             displayLinkConditions.needsToBeProactive = value
         }
 
+    var opaque: Boolean = true
+        set(value) {
+            field = value
+
+            updateLayerOpacity()
+        }
+
     /**
      * `true` if Metal rendering is synchronized with changes of UIKit interop views, `false` otherwise
      */
@@ -237,10 +243,14 @@ internal class MetalRedrawer(
 
             // If active, make metalLayer transparent, opaque otherwise.
             // Rendering into opaque CAMetalLayer allows direct-to-screen optimization.
-            metalLayer.setOpaque(!value && !transparency)
+            updateLayerOpacity()
             metalLayer.drawsAsynchronously = !value
         }
 
+    private fun updateLayerOpacity() {
+        metalLayer.setOpaque(!isInteropActive && opaque)
+    }
+
     /**
      * null after [dispose] call
      */
@@ -283,6 +293,8 @@ internal class MetalRedrawer(
             UIApplication.sharedApplication.applicationState != UIApplicationState.UIApplicationStateBackground
 
         caDisplayLink.addToRunLoop(NSRunLoop.mainRunLoop, NSRunLoopCommonModes)
+
+        updateLayerOpacity()
     }
 
     fun dispose() {
@@ -337,7 +349,7 @@ internal class MetalRedrawer(
                     height.toFloat()
                 )
             ).also { canvas ->
-                canvas.clear(if (transparency) Color.TRANSPARENT else Color.WHITE)
+                canvas.clear(if (metalLayer.opaque) Color.WHITE else Color.TRANSPARENT)
                 callbacks.render(canvas, lastRenderTimestamp)
             }
 

compose/ui/ui/src/uikitMain/kotlin/androidx/compose/ui/window/RenderingUIView.uikit.kt

@@ -32,7 +32,6 @@ import platform.UIKit.*
 
 internal class RenderingUIView(
     private val renderDelegate: Delegate,
-    private val transparency: Boolean,
 ) : UIView(
     frame = CGRectMake(
         x = 0.0,
@@ -68,13 +67,17 @@ internal class RenderingUIView(
 
             override fun retrieveInteropTransaction(): UIKitInteropTransaction =
                 renderDelegate.retrieveInteropTransaction()
-        },
-        transparency = transparency,
+        }
     )
 
+    override fun setOpaque(opaque: Boolean) {
+        super.setOpaque(opaque)
+
+        redrawer.opaque = opaque
+    }
+
     init {
         userInteractionEnabled = false
-        opaque = !transparency
 
         metalLayer.also {
             // Workaround for KN compiler bug
@@ -87,7 +90,6 @@ internal class RenderingUIView(
                 it.backgroundColor =
                     CGColorCreate(CGColorSpaceCreateDeviceRGB(), pinned.addressOf(0))
             }
-            it.setOpaque(!transparency)//todo check if remove
             it.framebufferOnly = false
         }
     }