Optimizations for Metal offscreen rendering for Swing interop (#765)

* Reuse Metal texture if size is not changed

* Reuse bitmap storage and recreate it only when size is changed

* Reuse ByteArrays if size is not changed

skiko/src/awtMain/kotlin/org/jetbrains/skiko/swing/MetalSwingRedrawer.kt

@@ -33,6 +33,12 @@ internal class MetalSwingRedrawer(
     }
     private val context: DirectContext = makeMetalContext()
 
+    private var texturePtr: Long = 0
+
+    private val storage = Bitmap()
+
+    private var bytesToDraw = ByteArray(0)
+
     init {
         onContextInit()
     }
@@ -40,6 +46,9 @@ internal class MetalSwingRedrawer(
     private val swingOffscreenDrawer = SwingOffscreenDrawer(swingLayerProperties)
 
     override fun dispose() {
+        bytesToDraw = ByteArray(0)
+        storage.close()
+        disposeMetalTexture(texturePtr)
         adapter.dispose()
         super.dispose()
     }
@@ -47,7 +56,8 @@ internal class MetalSwingRedrawer(
     override fun onRender(g: Graphics2D, width: Int, height: Int, nanoTime: Long) {
         autoreleasepool {
             autoCloseScope {
-                val renderTarget = makeRenderTarget(width, height).autoClose()
+                texturePtr = makeMetalTexture(adapter.ptr, texturePtr, width, height)
+                val renderTarget = makeRenderTarget().autoClose()
                 val surface = Surface.makeFromBackendRenderTarget(
                     context,
                     renderTarget,
@@ -71,15 +81,17 @@ internal class MetalSwingRedrawer(
         val width = surface.width
         val height = surface.height
 
-        val storage = Bitmap()
-        storage.setImageInfo(ImageInfo.makeN32Premul(width, height))
-        storage.allocPixels()
+        val dstRowBytes = width * 4
+        if (storage.width != width || storage.height != height) {
+            storage.allocPixelsFlags(ImageInfo.makeS32(width, height, ColorAlphaType.PREMUL), false)
+            bytesToDraw = ByteArray(storage.getReadPixelsArraySize(dstRowBytes = dstRowBytes))
+        }
         // TODO: it copies pixels from GPU to CPU, so it is really slow
         surface.readPixels(storage, 0, 0)
 
-        val bytes = storage.readPixels(storage.imageInfo, (width * 4), 0, 0)
-        if (bytes != null) {
-            swingOffscreenDrawer.draw(g, bytes, width, height)
+        val successfulRead = storage.readPixels(bytesToDraw, dstRowBytes = dstRowBytes)
+        if (successfulRead) {
+            swingOffscreenDrawer.draw(g, bytesToDraw, width, height)
         }
     }
 
@@ -89,8 +101,8 @@ internal class MetalSwingRedrawer(
                 "Total VRAM: ${adapter.memorySize / 1024 / 1024} MB\n"
     }
 
-    private fun makeRenderTarget(width: Int, height: Int) = BackendRenderTarget(
-        makeMetalRenderTargetOffScreen(adapter.ptr, width, height)
+    private fun makeRenderTarget() = BackendRenderTarget(
+        makeMetalRenderTargetOffScreen(texturePtr)
     )
 
     private fun makeMetalContext(): DirectContext = DirectContext(
@@ -99,5 +111,13 @@ internal class MetalSwingRedrawer(
 
     private external fun makeMetalContext(adapter: Long): Long
 
-    private external fun makeMetalRenderTargetOffScreen(adapter: Long, width: Int, height: Int): Long
+    private external fun makeMetalRenderTargetOffScreen(texture: Long): Long
+
+    /**
+     * Provides Metal texture taking given [oldTexture] into account
+     * since it can be reused if width and height are not changed,
+     * or the new one will be created.
+     */
+    private external fun makeMetalTexture(adapter: Long, oldTexture: Long, width: Int, height: Int): Long
+    private external fun disposeMetalTexture(texture: Long): Long
 }
\ No newline at end of file

skiko/src/awtMain/objectiveC/macos/MetalSwingRedrawer.mm

@@ -26,17 +26,38 @@ JNIEXPORT jlong JNICALL Java_org_jetbrains_skiko_swing_MetalSwingRedrawer_makeMe
     }
 }
 
+JNIEXPORT jlong JNICALL Java_org_jetbrains_skiko_swing_MetalSwingRedrawer_makeMetalTexture(
+        JNIEnv *env, jobject contextHandler, jlong adapterPtr, jlong oldTexturePtr, jint width, jint height
+) {
+    @autoreleasepool {
+        id <MTLTexture> oldTexture = (__bridge_transfer id <MTLTexture>) (void *) oldTexturePtr;
+        id <MTLTexture> metalTexture;
+        if (oldTexture == nil || oldTexture.width != width || oldTexture.height != height) {
+            id <MTLDevice> adapter = (__bridge id <MTLDevice>) (void *) adapterPtr;
+            MTLTextureDescriptor *textureDescriptor = [MTLTextureDescriptor texture2DDescriptorWithPixelFormat:MTLPixelFormatBGRA8Unorm width:width height:height mipmapped:NO];
+            metalTexture = [adapter newTextureWithDescriptor:textureDescriptor];
+        } else {
+            metalTexture = oldTexture;
+        }
+
+        return (jlong) (__bridge_retained void *) metalTexture;
+    }
+}
+
+JNIEXPORT void JNICALL Java_org_jetbrains_skiko_swing_MetalSwingRedrawer_disposeMetalTexture(JNIEnv *env, jobject contextHandler, jlong texturePtr) {
+    @autoreleasepool {
+        id <MTLTexture> oldTexture = (__bridge_transfer id <MTLTexture>) (void *) texturePtr;
+    }
+}
+
 JNIEXPORT jlong JNICALL Java_org_jetbrains_skiko_swing_MetalSwingRedrawer_makeMetalRenderTargetOffScreen(
-        JNIEnv *env, jobject contextHandler, jlong adapterPtr, jint width, jint height) {
+        JNIEnv *env, jobject contextHandler, jlong texturePtr) {
     @autoreleasepool {
-        id <MTLDevice> adapter = (__bridge id <MTLDevice>) (void *) adapterPtr;
-        MTLTextureDescriptor *textureDescriptor = [MTLTextureDescriptor texture2DDescriptorWithPixelFormat:MTLPixelFormatBGRA8Unorm width:width height:height mipmapped:NO];
-        // TODO: use double buffer
-        id <MTLTexture> metalTexture = [adapter newTextureWithDescriptor:textureDescriptor];
+        id <MTLTexture> texture = (__bridge id <MTLTexture>) (void *) texturePtr;
         GrMtlTextureInfo info;
-        info.fTexture.retain((__bridge GrMTLHandle) metalTexture);
+        info.fTexture.retain((__bridge GrMTLHandle) texture);
         GrBackendRenderTarget *renderTarget = NULL;
-        renderTarget = new GrBackendRenderTarget(width, height, 0, info);
+        renderTarget = new GrBackendRenderTarget(texture.width, texture.height, 0, info);
         return (jlong) renderTarget;
     }
 }

skiko/src/commonMain/kotlin/org/jetbrains/skia/Bitmap.kt

@@ -918,12 +918,32 @@ class Bitmap internal constructor(ptr: NativePointer) : Managed(ptr, _FinalizerH
         srcX: Int = 0,
         srcY: Int = 0
     ): ByteArray? {
-        return try {
-            val size = min(dstInfo.height, height - srcY) * dstRowBytes
+        val size = getReadPixelsArraySize(dstInfo, dstRowBytes, srcY)
+        val bitmapPixels = ByteArray(size)
+        val successfulRead = readPixels(bitmapPixels, dstInfo, dstRowBytes, srcX, srcY)
+        return bitmapPixels.takeIf { successfulRead }
+    }
 
+    /**
+     * See documentation for [readPixels]
+     *
+     * @param byteArray array where pixels will be read.
+     */
+    internal fun readPixels(
+        byteArray: ByteArray,
+        dstInfo: ImageInfo = imageInfo,
+        dstRowBytes: Int = rowBytes,
+        srcX: Int = 0,
+        srcY: Int = 0
+    ): Boolean {
+        check(byteArray.size == getReadPixelsArraySize(dstInfo, dstRowBytes, srcY)) {
+            "byteArray is not properly allocated. Use readPixelsArraySize"
+        }
+        try {
             Stats.onNativeCall()
-            withNullableResult(ByteArray(size)) {
-                _nReadPixels(
+            interopScope {
+                val byteArrayHandle = toInteropForResult(byteArray)
+                val successfulRead = _nReadPixels(
                     _ptr,
                     dstInfo.width,
                     dstInfo.height,
@@ -933,8 +953,12 @@ class Bitmap internal constructor(ptr: NativePointer) : Managed(ptr, _FinalizerH
                     dstRowBytes,
                     srcX,
                     srcY,
-                    it
+                    byteArrayHandle
                 )
+                if (successfulRead) {
+                    byteArrayHandle.fromInterop(byteArray)
+                }
+                return successfulRead
             }
         } finally {
             reachabilityBarrier(this)
@@ -942,6 +966,12 @@ class Bitmap internal constructor(ptr: NativePointer) : Managed(ptr, _FinalizerH
         }
     }
 
+    internal fun getReadPixelsArraySize(
+        dstInfo: ImageInfo = imageInfo,
+        dstRowBytes: Int = rowBytes,
+        srcY: Int = 0
+    ): Int = min(dstInfo.height, height - srcY) * dstRowBytes
+
     /**
      *
      * Sets dst to alpha described by pixels. Returns false if dst cannot