iOS postpone CAMetalDrawable acqusition

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

@@ -48,6 +48,7 @@ import kotlinx.cinterop.ObjCAction
 import kotlinx.cinterop.readValue
 import kotlinx.cinterop.useContents
 import kotlinx.coroutines.Dispatchers
+import org.jetbrains.skia.Canvas
 import org.jetbrains.skia.Surface
 import org.jetbrains.skiko.OS
 import org.jetbrains.skiko.OSVersion
@@ -642,7 +643,7 @@ internal actual class ComposeWindow : UIViewController {
             override fun retrieveInteropTransaction(): UIKitInteropTransaction =
                 interopContext.retrieve()
 
-            override fun draw(surface: Surface, targetTimestamp: NSTimeInterval) {
+            override fun render(canvas: Canvas, targetTimestamp: NSTimeInterval) {
                 // The calculation is split in two instead of
                 // `(targetTimestamp * 1e9).toLong()`
                 // to avoid losing precision for fractional part
@@ -652,7 +653,7 @@ internal actual class ComposeWindow : UIViewController {
                 val nanos =
                     integral.roundToLong() * secondsToNanos + (fractional * 1e9).roundToLong()
 
-                scene.render(surface.canvas, nanos)
+                scene.render(canvas, nanos)
             }
         }
 

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

@@ -32,6 +32,8 @@ import platform.QuartzCore.*
 import platform.UIKit.UIApplicationDidEnterBackgroundNotification
 import platform.UIKit.UIApplicationWillEnterForegroundNotification
 import platform.darwin.*
+import kotlin.math.roundToInt
+import org.jetbrains.skia.Rect
 import platform.Foundation.NSTimeInterval
 import platform.UIKit.UIApplication
 import platform.UIKit.UIApplicationState
@@ -149,12 +151,12 @@ private class ApplicationStateListener(
 
 internal interface MetalRedrawerCallbacks {
     /**
-     * Draw into a surface.
+     * Perform time step and encode draw operations into canvas.
      *
-     * @param surface The surface to be drawn.
+     * @param canvas Canvas to encode draw operations into.
      * @param targetTimestamp Timestamp indicating the expected draw result presentation time. Implementation should forward its internal time clock to this targetTimestamp to achieve smooth visual change cadence.
      */
-    fun draw(surface: Surface, targetTimestamp: NSTimeInterval)
+    fun render(canvas: Canvas, targetTimestamp: NSTimeInterval)
 
     /**
      * Retrieve a transaction object, containing a list of pending actions
@@ -177,6 +179,7 @@ internal class MetalRedrawer(
     private val context = DirectContext.makeMetal(device.objcPtr(), queue.objcPtr())
     private val inflightCommandBuffers = mutableListOf<MTLCommandBufferProtocol>()
     private var lastRenderTimestamp: NSTimeInterval = CACurrentMediaTime()
+    private val pictureRecorder = PictureRecorder()
 
     // Semaphore for preventing command buffers count more than swapchain size to be scheduled/executed at the same time
     private val inflightSemaphore =
@@ -267,6 +270,8 @@ internal class MetalRedrawer(
         caDisplayLink?.invalidate()
         caDisplayLink = null
 
+        pictureRecorder.close()
+
         context.flush()
         context.close()
     }
@@ -302,13 +307,27 @@ internal class MetalRedrawer(
                 return@autoreleasepool
             }
 
+            // Perform timestep and record all draw commands into [Picture]
+            pictureRecorder.beginRecording(Rect(
+                left = 0f,
+                top = 0f,
+                width.toFloat(),
+                height.toFloat()
+            )).also { canvas ->
+                canvas.clear(Color.WHITE)
+                callbacks.render(canvas, lastRenderTimestamp)
+            }
+
+            val picture = pictureRecorder.finishRecordingAsPicture()
+
             dispatch_semaphore_wait(inflightSemaphore, DISPATCH_TIME_FOREVER)
 
             val metalDrawable = metalLayer.nextDrawable()
 
             if (metalDrawable == null) {
                 // TODO: anomaly, log
                 // Logger.warn { "'metalLayer.nextDrawable()' returned null. 'metalLayer.allowsNextDrawableTimeout' should be set to false. Skipping the frame." }
+                picture.close()
                 dispatch_semaphore_signal(inflightSemaphore)
                 return@autoreleasepool
             }
@@ -328,14 +347,14 @@ internal class MetalRedrawer(
             if (surface == null) {
                 // TODO: anomaly, log
                 // Logger.warn { "'Surface.makeFromBackendRenderTarget' returned null. Skipping the frame." }
+                picture.close()
                 renderTarget.close()
-                // TODO: manually release metalDrawable when K/N API arrives
                 dispatch_semaphore_signal(inflightSemaphore)
                 return@autoreleasepool
             }
 
-            surface.canvas.clear(Color.WHITE)
-            callbacks.draw(surface, lastRenderTimestamp)
+            surface.canvas.drawPicture(picture)
+            picture.close()
             surface.flushAndSubmit()
 
             val interopTransaction = callbacks.retrieveInteropTransaction()

compose/ui/ui/src/uikitMain/kotlin/androidx/compose/ui/window/SkikoUIView.kt

@@ -32,6 +32,7 @@ import platform.QuartzCore.CAMetalLayer
 import platform.UIKit.*
 import platform.darwin.NSInteger
 import org.jetbrains.skia.Surface
+import org.jetbrains.skia.Canvas
 import org.jetbrains.skiko.SkikoInputModifiers
 import org.jetbrains.skiko.SkikoKey
 import org.jetbrains.skiko.SkikoKeyboardEvent
@@ -51,7 +52,7 @@ internal interface SkikoUIViewDelegate {
 
     fun retrieveInteropTransaction(): UIKitInteropTransaction
 
-    fun draw(surface: Surface, targetTimestamp: NSTimeInterval)
+    fun render(canvas: Canvas, targetTimestamp: NSTimeInterval)
 }
 
 @Suppress("CONFLICTING_OVERLOADS")
@@ -79,8 +80,8 @@ internal class SkikoUIView : UIView, UIKeyInputProtocol, UITextInputProtocol {
     private val _redrawer: MetalRedrawer = MetalRedrawer(
         _metalLayer,
         callbacks = object : MetalRedrawerCallbacks {
-            override fun draw(surface: Surface, targetTimestamp: NSTimeInterval) {
-                delegate?.draw(surface, targetTimestamp)
+            override fun render(canvas: Canvas, targetTimestamp: NSTimeInterval) {
+                delegate?.render(canvas, targetTimestamp)
             }
 
             override fun retrieveInteropTransaction(): UIKitInteropTransaction =