External Texture support for macOS Metal

ci/licenses_golden/licenses_flutter

@@ -1109,6 +1109,8 @@ FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterEngin
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterExternalTextureGL.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterExternalTextureGL.mm
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterExternalTextureMetal.h
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterExternalTextureMetal.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterFrameBufferProvider.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterFrameBufferProvider.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterGLCompositor.h
@@ -1118,6 +1120,7 @@ FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterIOSur
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterIOSurfaceHolder.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterIntermediateKeyResponder.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterIntermediateKeyResponder.mm
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMacOSExternalTexture.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalRenderer.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalRenderer.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalRendererTest.mm
@@ -1138,6 +1141,8 @@ FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterTextI
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterTextInputModel.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterTextInputPlugin.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterTextInputPlugin.mm
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterTextureRegistrar.h
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterTextureRegistrar.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterView.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterView.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterViewController.mm

shell/platform/darwin/macos/BUILD.gn

@@ -63,6 +63,8 @@ source_set("flutter_framework_source") {
     "framework/Source/FlutterEngine_Internal.h",
     "framework/Source/FlutterExternalTextureGL.h",
     "framework/Source/FlutterExternalTextureGL.mm",
+    "framework/Source/FlutterExternalTextureMetal.h",
+    "framework/Source/FlutterExternalTextureMetal.mm",
     "framework/Source/FlutterFrameBufferProvider.h",
     "framework/Source/FlutterFrameBufferProvider.mm",
     "framework/Source/FlutterGLCompositor.h",
@@ -71,6 +73,8 @@ source_set("flutter_framework_source") {
     "framework/Source/FlutterIOSurfaceHolder.mm",
     "framework/Source/FlutterIntermediateKeyResponder.h",
     "framework/Source/FlutterIntermediateKeyResponder.mm",
+    "framework/Source/FlutterMacOSExternalTexture.h",
+    "framework/Source/FlutterMacOSExternalTexture.h",
     "framework/Source/FlutterMetalRenderer.h",
     "framework/Source/FlutterMetalRenderer.mm",
     "framework/Source/FlutterMouseCursorPlugin.h",
@@ -88,6 +92,8 @@ source_set("flutter_framework_source") {
     "framework/Source/FlutterTextInputModel.mm",
     "framework/Source/FlutterTextInputPlugin.h",
     "framework/Source/FlutterTextInputPlugin.mm",
+    "framework/Source/FlutterTextureRegistrar.h",
+    "framework/Source/FlutterTextureRegistrar.mm",
     "framework/Source/FlutterView.h",
     "framework/Source/FlutterView.mm",
     "framework/Source/FlutterViewController.mm",
@@ -104,6 +110,7 @@ source_set("flutter_framework_source") {
     "//flutter/fml",
     "//flutter/shell/platform/common:common_cpp_switches",
     "//flutter/shell/platform/darwin/common:framework_shared",
+    "//flutter/shell/platform/darwin/graphics:graphics",
     "//flutter/shell/platform/embedder:embedder_as_internal_library",
     "//third_party/skia",
   ]

shell/platform/darwin/macos/framework/Source/FlutterExternalTextureGL.h

@@ -4,17 +4,16 @@
 
 #import <Foundation/Foundation.h>
 
-#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterTexture.h"
-#import "flutter/shell/platform/embedder/embedder.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterMacOSExternalTexture.h"
 
 /**
  * Used to bridge FlutterTexture object and handle the texture copy request the
  * Flutter engine.
  */
-@interface FlutterExternalTextureGL : NSObject
+@interface FlutterExternalTextureGL : NSObject <FlutterMacOSExternalTexture>
 
 /**
- * Initializes a texture adapter with |texture| return a instance.
+ * Initializes a texture adapter with |texture|.
  */
 - (nonnull instancetype)initWithFlutterTexture:(nonnull id<FlutterTexture>)texture;
 
@@ -26,9 +25,4 @@
  */
 - (BOOL)populateTexture:(nonnull FlutterOpenGLTexture*)openGLTexture;
 
-/**
- * Returns the ID for the FlutterTexture instance.
- */
-- (int64_t)textureID;
-
 @end

shell/platform/darwin/macos/framework/Source/FlutterExternalTextureMetal.h

@@ -0,0 +1,30 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import <Foundation/Foundation.h>
+
+#import "flutter/shell/platform/darwin/graphics/FlutterDarwinContextMetal.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterMacOSExternalTexture.h"
+
+/**
+ * Used to bridge FlutterTexture object and handle the texture copy request the
+ * Flutter engine.
+ */
+@interface FlutterExternalTextureMetal : NSObject <FlutterMacOSExternalTexture>
+
+/**
+ * Initializes a texture adapter with |texture|.
+ */
+- (nonnull instancetype)initWithFlutterTexture:(nonnull id<FlutterTexture>)texture
+                            darwinMetalContext:(nonnull FlutterDarwinContextMetal*)context;
+
+/**
+ * Accepts texture buffer copy request from the Flutter engine.
+ * When the user side marks the textureID as available, the Flutter engine will
+ * callback to this method and ask for populate the |metalTexture| object,
+ * such as the texture type and the format of the pixel buffer and the texture object.
+ */
+- (BOOL)populateTexture:(nonnull FlutterMetalExternalTexture*)metalTexture;
+
+@end

shell/platform/darwin/macos/framework/Source/FlutterExternalTextureMetal.mm

@@ -0,0 +1,75 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterExternalTextureMetal.h"
+
+@implementation FlutterExternalTextureMetal {
+  FlutterDarwinContextMetal* _darwinMetalContext;
+
+  int64_t _textureID;
+
+  id<FlutterTexture> _texture;
+
+  id<MTLTexture> _mtlTexture;
+}
+
+- (instancetype)initWithFlutterTexture:(id<FlutterTexture>)texture
+                    darwinMetalContext:(FlutterDarwinContextMetal*)context {
+  self = [super init];
+  if (self) {
+    _texture = texture;
+    _textureID = reinterpret_cast<int64_t>(_texture);
+    _darwinMetalContext = context;
+  }
+  return self;
+}
+
+- (int64_t)textureID {
+  return _textureID;
+}
+
+- (BOOL)populateTexture:(FlutterMetalExternalTexture*)textureOut {
+  // Copy the pixel buffer from the FlutterTexture instance implemented on the user side.
+  CVPixelBufferRef pixelBuffer = [_texture copyPixelBuffer];
+
+  if (!pixelBuffer) {
+    return NO;
+  }
+
+  SkISize textureSize =
+      SkISize::Make(CVPixelBufferGetWidth(pixelBuffer), CVPixelBufferGetHeight(pixelBuffer));
+
+  CVMetalTextureRef cvMetalTexture = nullptr;
+  CVReturn cvReturn =
+      CVMetalTextureCacheCreateTextureFromImage(/*allocator=*/kCFAllocatorDefault,
+                                                /*textureCache=*/_darwinMetalContext.textureCache,
+                                                /*sourceImage=*/pixelBuffer,
+                                                /*textureAttributes=*/nullptr,
+                                                /*pixelFormat=*/MTLPixelFormatBGRA8Unorm,
+                                                /*width=*/textureSize.width(),
+                                                /*height=*/textureSize.height(),
+                                                /*planeIndex=*/0u,
+                                                /*texture=*/&cvMetalTexture);
+
+  if (cvReturn != kCVReturnSuccess) {
+    NSLog(@"Could not create Metal texture from pixel buffer: CVReturn %d", cvReturn);
+    return NO;
+  }
+
+  _mtlTexture = CVMetalTextureGetTexture(cvMetalTexture);
+  CVBufferRelease(cvMetalTexture);
+
+  std::vector<FlutterMetalTextureHandle> textures = {
+      (__bridge FlutterMetalTextureHandle)_mtlTexture};
+
+  textureOut->num_textures = 1;
+  textureOut->height = textureSize.height();
+  textureOut->width = textureSize.width();
+  textureOut->pixel_format = FlutterMetalExternalTexturePixelFormat::kRGBA;
+  textureOut->textures = textures.data();
+
+  return YES;
+}
+
+@end

shell/platform/darwin/macos/framework/Source/FlutterMacOSExternalTexture.h

@@ -0,0 +1,20 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import <Foundation/Foundation.h>
+
+#import "flutter/shell/platform/darwin/common/framework/Headers/FlutterTexture.h"
+#import "flutter/shell/platform/embedder/embedder.h"
+
+/*
+ * Embedding side texture wrappers for GL and Metal external textures.
+ */
+@protocol FlutterMacOSExternalTexture
+
+/**
+ * Returns the ID for the FlutterTexture instance.
+ */
+- (int64_t)textureID;
+
+@end

shell/platform/darwin/macos/framework/Source/FlutterMetalRenderer.h

@@ -12,7 +12,7 @@
  * FlutterEngine creation and then attached to the FlutterView once the FlutterViewController is
  * initialized.
  */
-@interface FlutterMetalRenderer : NSObject <FlutterRenderer>
+@interface FlutterMetalRenderer : FlutterTextureRegistrar <FlutterRenderer>
 
 /**
  * Interface to the system GPU. Used to issue all the rendering commands.
@@ -34,4 +34,10 @@
  */
 - (BOOL)present:(int64_t)textureID;
 
+/**
+ * Populates the texture registry with the provided metalTexture.
+ */
+- (BOOL)populateTextureWithIdentifier:(int64_t)textureID
+                         metalTexture:(nonnull FlutterMetalExternalTexture*)metalTexture;
+
 @end

shell/platform/darwin/macos/framework/Source/FlutterMetalRenderer.mm

@@ -6,6 +6,7 @@
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterMetalRenderer.h"
 
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterExternalTextureMetal.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterView.h"
 #include "flutter/shell/platform/embedder/embedder.h"
 
@@ -23,16 +24,27 @@ static bool OnPresentDrawable(FlutterEngine* engine, const FlutterMetalTexture*
   return [metalRenderer present:texture->texture_id];
 }
 
+static bool OnAcquireExternalTexture(FlutterEngine* engine,
+                                     int64_t textureIdentifier,
+                                     size_t width,
+                                     size_t height,
+                                     FlutterMetalExternalTexture* metalTexture) {
+  FlutterMetalRenderer* metalRenderer = reinterpret_cast<FlutterMetalRenderer*>(engine.renderer);
+  return [metalRenderer populateTextureWithIdentifier:textureIdentifier metalTexture:metalTexture];
+}
+
 #pragma mark - FlutterMetalRenderer implementation
 
 @implementation FlutterMetalRenderer {
   __weak FlutterEngine* _engine;
 
   FlutterView* _flutterView;
+
+  FlutterDarwinContextMetal* _darwinMetalContext;
 }
 
 - (instancetype)initWithFlutterEngine:(nonnull FlutterEngine*)flutterEngine {
-  self = [super init];
+  self = [super initWithDelegate:self engine:flutterEngine];
   if (self) {
     _engine = flutterEngine;
 
@@ -47,6 +59,9 @@ - (instancetype)initWithFlutterEngine:(nonnull FlutterEngine*)flutterEngine {
       NSLog(@"Could not create Metal command queue.");
       return nil;
     }
+
+    _darwinMetalContext = [[FlutterDarwinContextMetal alloc] initWithMTLDevice:_device
+                                                                  commandQueue:_commandQueue];
   }
   return self;
 }
@@ -65,6 +80,8 @@ - (FlutterRendererConfig)createRendererConfig {
           reinterpret_cast<FlutterMetalTextureCallback>(OnGetNextDrawable),
       .metal.present_drawable_callback =
           reinterpret_cast<FlutterMetalPresentCallback>(OnPresentDrawable),
+      .metal.external_texture_frame_callback =
+          reinterpret_cast<FlutterMetalTextureFrameCallback>(OnAcquireExternalTexture),
   };
   return config;
 }
@@ -92,20 +109,17 @@ - (BOOL)present:(int64_t)textureID {
 
 #pragma mark - FlutterTextureRegistrar methods.
 
-- (int64_t)registerTexture:(id<FlutterTexture>)texture {
-  NSAssert(NO, @"External textures aren't yet supported when using Metal on macOS."
-                " See: https://github.com/flutter/flutter/issues/73826");
-  return 0;
-}
-
-- (void)textureFrameAvailable:(int64_t)textureID {
-  NSAssert(NO, @"External textures aren't yet supported when using Metal on macOS."
-                " See: https://github.com/flutter/flutter/issues/73826");
+- (BOOL)populateTextureWithIdentifier:(int64_t)textureID
+                         metalTexture:(FlutterMetalExternalTexture*)textureOut {
+  id<FlutterMacOSExternalTexture> texture = [self getTextureWithID:textureID];
+  FlutterExternalTextureMetal* metalTexture =
+      reinterpret_cast<FlutterExternalTextureMetal*>(texture);
+  return [metalTexture populateTexture:textureOut];
 }
 
-- (void)unregisterTexture:(int64_t)textureID {
-  NSAssert(NO, @"External textures aren't yet supported when using Metal on macOS."
-                " See: https://github.com/flutter/flutter/issues/73826");
+- (id<FlutterMacOSExternalTexture>)onRegisterTexture:(id<FlutterTexture>)texture {
+  return [[FlutterExternalTextureMetal alloc] initWithFlutterTexture:texture
+                                                  darwinMetalContext:_darwinMetalContext];
 }
 
 @end

shell/platform/darwin/macos/framework/Source/FlutterOpenGLRenderer.h

@@ -11,7 +11,7 @@
  * texture management. This is initialized during FlutterEngine creation and then attached to the
  * FlutterView once the FlutterViewController is initializer.
  */
-@interface FlutterOpenGLRenderer : NSObject <FlutterRenderer>
+@interface FlutterOpenGLRenderer : FlutterTextureRegistrar <FlutterRenderer>
 
 /**
  * The resource context used by the engine for texture uploads. FlutterViews associated with this

shell/platform/darwin/macos/framework/Source/FlutterOpenGLRenderer.mm

@@ -57,17 +57,13 @@ @implementation FlutterOpenGLRenderer {
   // The context provided to the Flutter engine for resource loading.
   NSOpenGLContext* _resourceContext;
 
-  // A mapping of textureID to internal FlutterExternalTextureGL adapter.
-  NSMutableDictionary<NSNumber*, FlutterExternalTextureGL*>* _textures;
-
   __weak FlutterEngine* _flutterEngine;
 }
 
 - (instancetype)initWithFlutterEngine:(FlutterEngine*)flutterEngine {
-  self = [super init];
+  self = [super initWithDelegate:self engine:flutterEngine];
   if (self) {
     _flutterEngine = flutterEngine;
-    _textures = [[NSMutableDictionary alloc] init];
   }
   return self;
 }
@@ -136,37 +132,13 @@ - (BOOL)makeResourceCurrent {
 
 - (BOOL)populateTextureWithIdentifier:(int64_t)textureID
                         openGLTexture:(FlutterOpenGLTexture*)openGLTexture {
-  return [_textures[@(textureID)] populateTexture:openGLTexture];
-}
-
-- (int64_t)registerTexture:(id<FlutterTexture>)texture {
-  FlutterExternalTextureGL* externalTexture =
-      [[FlutterExternalTextureGL alloc] initWithFlutterTexture:texture];
-  int64_t textureID = [externalTexture textureID];
-  BOOL success = [_flutterEngine registerTextureWithID:textureID];
-  if (success) {
-    _textures[@(textureID)] = externalTexture;
-    return textureID;
-  } else {
-    NSLog(@"Unable to register the texture with id: %lld.", textureID);
-    return 0;
-  }
-}
-
-- (void)textureFrameAvailable:(int64_t)textureID {
-  BOOL success = [_flutterEngine markTextureFrameAvailable:textureID];
-  if (!success) {
-    NSLog(@"Unable to mark texture with id %lld as available.", textureID);
-  }
+  id<FlutterMacOSExternalTexture> texture = [self getTextureWithID:textureID];
+  FlutterExternalTextureGL* glTexture = reinterpret_cast<FlutterExternalTextureGL*>(texture);
+  return [glTexture populateTexture:openGLTexture];
 }
 
-- (void)unregisterTexture:(int64_t)textureID {
-  bool success = [_flutterEngine unregisterTextureWithID:textureID];
-  if (success) {
-    [_textures removeObjectForKey:@(textureID)];
-  } else {
-    NSLog(@"Unable to unregister texture with id: %lld.", textureID);
-  }
+- (id<FlutterMacOSExternalTexture>)onRegisterTexture:(id<FlutterTexture>)texture {
+  return [[FlutterExternalTextureGL alloc] initWithFlutterTexture:texture];
 }
 
 - (FlutterRendererConfig)createRendererConfig {

shell/platform/darwin/macos/framework/Source/FlutterRenderer.h

@@ -5,13 +5,14 @@
 #import <Cocoa/Cocoa.h>
 
 #import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterEngine.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterTextureRegistrar.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterView.h"
 #import "flutter/shell/platform/embedder/embedder.h"
 
 /**
  * Rendering backend agnostic FlutterRendererConfig provider to be used by the embedder API.
  */
-@protocol FlutterRenderer <FlutterTextureRegistry>
+@protocol FlutterRenderer <FlutterTextureRegistry, FlutterTextureRegistrarDelegate>
 
 /**
  * Intializes the renderer with the given FlutterEngine.

shell/platform/darwin/macos/framework/Source/FlutterTextureRegistrar.h

@@ -0,0 +1,48 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import <Cocoa/Cocoa.h>
+
+#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterEngine.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterMacOSExternalTexture.h"
+
+/*
+ * Delegate methods for FlutterTextureRegistrar.
+ */
+@protocol FlutterTextureRegistrarDelegate
+
+/*
+ * Called by the FlutterTextureRegistrar when a texture is registered.
+ */
+- (nonnull id<FlutterMacOSExternalTexture>)onRegisterTexture:(nonnull id<FlutterTexture>)texture;
+
+@end
+
+/*
+ * Holds the external textures and implements the FlutterTextureRegistry.
+ */
+@interface FlutterTextureRegistrar : NSObject <FlutterTextureRegistry>
+
+/*
+ * Use `initWithDelegate:engine:` instead.
+ */
+- (nullable instancetype)init NS_UNAVAILABLE;
+
+/*
+ * Use `initWithDelegate:engine:` instead.
+ */
++ (nullable instancetype)new NS_UNAVAILABLE;
+
+/*
+ * Initialzes the texture registrar.
+ */
+- (nullable instancetype)initWithDelegate:(nonnull id<FlutterTextureRegistrarDelegate>)delegate
+                                   engine:(nonnull FlutterEngine*)engine NS_DESIGNATED_INITIALIZER;
+
+/*
+ * Returns the registered texture with the provided `textureID`.
+ */
+- (nullable id<FlutterMacOSExternalTexture>)getTextureWithID:(int64_t)textureID;
+
+@end

shell/platform/darwin/macos/framework/Source/FlutterTextureRegistrar.mm

@@ -0,0 +1,67 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterTextureRegistrar.h"
+
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h"
+
+@implementation FlutterTextureRegistrar {
+  __weak id<FlutterTextureRegistrarDelegate> _delegate;
+
+  __weak FlutterEngine* _flutterEngine;
+
+  // A mapping of textureID to internal FlutterExternalTextureGL adapter.
+  NSMutableDictionary<NSNumber*, id<FlutterMacOSExternalTexture>>* _textures;
+}
+
+- (instancetype)init {
+  @throw([NSException exceptionWithName:@"FlutterTextureRegistrar must initWithDelegate"
+                                 reason:nil
+                               userInfo:nil]);
+}
+
+- (instancetype)initWithDelegate:(id<FlutterTextureRegistrarDelegate>)delegate
+                          engine:(FlutterEngine*)engine {
+  if (self = [super init]) {
+    _delegate = delegate;
+    _flutterEngine = engine;
+    _textures = [[NSMutableDictionary alloc] init];
+  }
+  return self;
+}
+
+- (int64_t)registerTexture:(id<FlutterTexture>)texture {
+  id<FlutterMacOSExternalTexture> externalTexture = [_delegate onRegisterTexture:texture];
+  int64_t textureID = [externalTexture textureID];
+  BOOL success = [_flutterEngine registerTextureWithID:textureID];
+  if (success) {
+    _textures[@(textureID)] = externalTexture;
+    return textureID;
+  } else {
+    NSLog(@"Unable to register the texture with id: %lld.", textureID);
+    return 0;
+  }
+}
+
+- (void)textureFrameAvailable:(int64_t)textureID {
+  BOOL success = [_flutterEngine markTextureFrameAvailable:textureID];
+  if (!success) {
+    NSLog(@"Unable to mark texture with id %lld as available.", textureID);
+  }
+}
+
+- (void)unregisterTexture:(int64_t)textureID {
+  bool success = [_flutterEngine unregisterTextureWithID:textureID];
+  if (success) {
+    [_textures removeObjectForKey:@(textureID)];
+  } else {
+    NSLog(@"Unable to unregister texture with id: %lld.", textureID);
+  }
+}
+
+- (id<FlutterMacOSExternalTexture>)getTextureWithID:(int64_t)textureID {
+  return _textures[@(textureID)];
+}
+
+@end

tools/gn

@@ -257,16 +257,17 @@ def to_gn_args(args):
       # attributes in release modes till the toolchain is updated.
       gn_args['skia_enable_api_available_macro'] = args.runtime_mode != "release"
 
-    if sys.platform == 'darwin' and args.macos_enable_metal:
+    if sys.platform == 'darwin' and args.target_os not in ['android', 'fuchsia']:
       # OpenGL is deprecated on macOS > 10.11.
       # This is not neccessarily needed but enabling this until we have a way to
       # build a macOS metal only shell and a gl only shell.
       gn_args['allow_deprecated_api_calls'] = True
       gn_args['skia_use_metal'] = True
-      gn_args['shell_enable_metal'] = True
-      # Skia has Metal support on macOS version >= 10.14.
-      MACOS_SKIA_METAL_SUPPORTED_MIN_VERSION = '10.14'
-      gn_args['mac_sdk_min'] = MACOS_SKIA_METAL_SUPPORTED_MIN_VERSION
+      if args.macos_enable_metal:
+        gn_args['shell_enable_metal'] = True
+        # Skia has Metal support on macOS version >= 10.14.
+        MACOS_SKIA_METAL_SUPPORTED_MIN_VERSION = '10.14'
+        gn_args['mac_sdk_min'] = MACOS_SKIA_METAL_SUPPORTED_MIN_VERSION
 
     if args.enable_vulkan:
       # Enable vulkan in the Flutter shell.