Postpone drawable acqusition

Author: elijah-semyonov

compose/ui/ui/src/skikoMain/kotlin/androidx/compose/ui/ComposeScene.skiko.kt

@@ -517,7 +517,14 @@ class ComposeScene internal constructor(
  * Render the current content on [canvas]. Passed [nanoTime] will be used to drive all
  * animations in the content (or any other code, which uses [withFrameNanos]
  */
- fun render(canvas: Canvas, nanoTime: Long): Unit = postponeInvalidation {
+ @Deprecated("Use `fun render(retrieveCanvas: () -> Canvas?, nanoTime: Long): Unit` instead")
+ fun render(canvas: Canvas, nanoTime: Long): Unit = render(retrieveCanvas = { canvas }, nanoTime)
+
+ /**
+ * Flush async operations, notify all animations and perform recomposition-layout-draw sequence.
+ * [Canvas] to draw on is retrieved lazily to postpone acquiring drawable as late as possible.
+ */
+ fun render(retrieveCanvas: () -> Canvas?, nanoTime: Long): Unit = postponeInvalidation {
  recomposeDispatcher.flush()
  frameClock.sendFrame(nanoTime) // Recomposition
  sendAndPerformSnapshotChanges() // Apply changes from recomposition phase to layout phase
@@ -526,7 +533,11 @@ class ComposeScene internal constructor(
  syntheticEventSender.updatePointerPosition()
  sendAndPerformSnapshotChanges() // Apply changes from layout phase to draw phase
  needDraw = false
- forEachOwner { it.draw(canvas) }
+
+ retrieveCanvas()?.let { canvas ->
+ forEachOwner { it.draw(canvas) }
+ }
+
  forEachOwner { it.clearInvalidObservations() }
  }
 

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

@@ -46,6 +46,7 @@ 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
@@ -637,7 +638,7 @@ internal actual class ComposeWindow : UIViewController {
  override fun retrieveCATransactionCommands(): List<() -> Unit> =
  interopContext.getActionsAndClear()
 
- override fun draw(surface: Surface, targetTimestamp: NSTimeInterval) {
+ override fun render(retrieveCanvas: () -> Canvas?, targetTimestamp: NSTimeInterval) {
  // The calculation is split in two instead of
  // `(targetTimestamp * 1e9).toLong()`
  // to avoid losing precision for fractional part
@@ -646,7 +647,7 @@ internal actual class ComposeWindow : UIViewController {
  val secondsToNanos = 1_000_000_000L
  val nanos = integral.roundToLong() * secondsToNanos + (fractional * 1e9).roundToLong()
 
- scene.render(surface.canvas, nanos)
+ scene.render(retrieveCanvas, nanos)
  }
  }
 

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

@@ -148,10 +148,10 @@ internal interface MetalRedrawerCallbacks {
  /**
  * Draw into a surface.
  *
- * @param surface The surface to be drawn.
+ * @param retrieveCanvas Callback to lazily retrieve canvas to postpone drawable acquiring.
  * @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(retrieveCanvas: () -> Canvas?, targetTimestamp: NSTimeInterval)
 
  /**
  * Retrieve a list of pending actions which need to be synchronized with Metal rendering using CATransaction mechanism.
@@ -272,6 +272,52 @@ internal class MetalRedrawer(
  draw(waitUntilCompletion = true, CACurrentMediaTime())
  }
 
+ private data class FrameRenderTarget(
+ val drawable: CAMetalDrawableProtocol,
+ val renderTarget: BackendRenderTarget,
+ val surface: Surface
+ ) {
+ fun dispose() {
+ surface.close()
+ renderTarget.close()
+ // TODO manually release metalDrawable when K/N API arrives
+ }
+ }
+
+ private fun createFrameRenderTarget(width: Int, height: Int): FrameRenderTarget? {
+ 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." }
+ dispatch_semaphore_signal(inflightSemaphore)
+ return null
+ }
+
+ val renderTarget =
+ BackendRenderTarget.makeMetal(width, height, metalDrawable.texture.objcPtr())
+
+ val surface = Surface.makeFromBackendRenderTarget(
+ context,
+ renderTarget,
+ SurfaceOrigin.TOP_LEFT,
+ SurfaceColorFormat.BGRA_8888,
+ ColorSpace.sRGB,
+ SurfaceProps(pixelGeometry = PixelGeometry.UNKNOWN)
+ )
+
+ if (surface == null) {
+ renderTarget.close()
+ // TODO: manually release metalDrawable when K/N API arrives
+ dispatch_semaphore_signal(inflightSemaphore)
+ return null
+ }
+
+ return FrameRenderTarget(metalDrawable, renderTarget, surface)
+ }
+
  private fun draw(waitUntilCompletion: Boolean, targetTimestamp: NSTimeInterval) {
  check(NSThread.isMainThread)
 
@@ -286,41 +332,21 @@ internal class MetalRedrawer(
  return@autoreleasepool
  }
 
- dispatch_semaphore_wait(inflightSemaphore, DISPATCH_TIME_FOREVER)
+ var frameRenderTarget: FrameRenderTarget? = null
 
- 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." }
- dispatch_semaphore_signal(inflightSemaphore)
- return@autoreleasepool
+ // Lambda which overwrites local frameRenderTarget if called, clears [Canvas] and returns it to the callee
+ val retrieveCanvas = {
+ createFrameRenderTarget(width, height)?.also {
+ frameRenderTarget = it
+ it.surface.canvas.clear(Color.WHITE)
+ }?.surface?.canvas
  }
 
- val renderTarget =
- BackendRenderTarget.makeMetal(width, height, metalDrawable.texture.objcPtr())
-
- val surface = Surface.makeFromBackendRenderTarget(
- context,
- renderTarget,
- SurfaceOrigin.TOP_LEFT,
- SurfaceColorFormat.BGRA_8888,
- ColorSpace.sRGB,
- SurfaceProps(pixelGeometry = PixelGeometry.UNKNOWN)
- )
-
- if (surface == null) {
- // TODO: anomaly, log
- // Logger.warn { "'Surface.makeFromBackendRenderTarget' returned null. Skipping the frame." }
- renderTarget.close()
- // TODO: manually release metalDrawable when K/N API arrives
- dispatch_semaphore_signal(inflightSemaphore)
- return@autoreleasepool
- }
+ callbacks.render(retrieveCanvas, lastRenderTimestamp)
 
- surface.canvas.clear(Color.WHITE)
- callbacks.draw(surface, lastRenderTimestamp)
- surface.flushAndSubmit()
+ // Wrap up all the rendering work, if callee of retrieveCanvas encoded any work, return otherwise
+ val nonNullFrameRenderTarget = frameRenderTarget ?: return@autoreleasepool
+ nonNullFrameRenderTarget.surface.flushAndSubmit()
 
  val caTransactionCommands = callbacks.retrieveCATransactionCommands()
  val presentsWithTransaction =
@@ -333,7 +359,7 @@ internal class MetalRedrawer(
 
  if (!presentsWithTransaction) {
  // If there are no pending changes in UIKit interop, present the drawable ASAP
- commandBuffer.presentDrawable(metalDrawable)
+ commandBuffer.presentDrawable(nonNullFrameRenderTarget.drawable)
  }
 
  commandBuffer.addCompletedHandler {
@@ -346,14 +372,12 @@ internal class MetalRedrawer(
  // If there are pending changes in UIKit interop, [waitUntilScheduled](https://developer.apple.com/documentation/metal/mtlcommandbuffer/1443036-waituntilscheduled) is called
  // to ensure that transaction is available
  commandBuffer.waitUntilScheduled()
- metalDrawable.present()
+ nonNullFrameRenderTarget.drawable.present()
  caTransactionCommands.fastForEach { it.invoke() }
  CATransaction.flush()
  }
 
- surface.close()
- renderTarget.close()
- // TODO manually release metalDrawable when K/N API arrives
+ nonNullFrameRenderTarget.dispose()
 
  // Track current inflight command buffers to synchronously wait for their schedule in case app goes background
  if (inflightCommandBuffers.size == metalLayer.maximumDrawableCount.toInt()) {

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

@@ -31,6 +31,7 @@ import platform.UIKit.*
 import platform.darwin.NSInteger
 import kotlin.math.max
 import kotlin.math.min
+import org.jetbrains.skia.Canvas
 import org.jetbrains.skia.Surface
 import org.jetbrains.skiko.SkikoInputModifiers
 import org.jetbrains.skiko.SkikoKey
@@ -51,7 +52,7 @@ internal interface SkikoUIViewDelegate {
 
  fun retrieveCATransactionCommands(): List<() -> Unit>
 
- fun draw(surface: Surface, targetTimestamp: NSTimeInterval)
+ fun render(retrieveCanvas: () -> 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(retrieveCanvas: () -> Canvas?, targetTimestamp: NSTimeInterval) {
+ delegate?.render(retrieveCanvas, targetTimestamp)
  }
 
  override fun retrieveCATransactionCommands(): List<() -> Unit> =