[macOS] Merge FlutterBackingStore implementations

Now that OpenGL support has been removed from the macOS embedder, we
merge FlutterRenderBackingStore and its only implementing subclass,
FlutterMetalRenderBackingStore, and similarly
FlutterRenderBackingStoreProvider and its only implementing subclass
FlutterMetalRenderBackingStoreProvider.

Issue: flutter/flutter#108304
Issue: flutter/flutter#114445

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

@@ -11,13 +11,6 @@
  */
 @interface FlutterRenderBackingStore : NSObject
 
-@end
-
-/**
- * Wraps a Metal texture.
- */
-@interface FlutterMetalRenderBackingStore : FlutterRenderBackingStore
-
 /**
  * MTLTexture referenced by this backing store instance.
  */

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

@@ -5,9 +5,6 @@
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterBackingStore.h"
 
 @implementation FlutterRenderBackingStore
-@end
-
-@implementation FlutterMetalRenderBackingStore
 
 - (instancetype)initWithTexture:(id<MTLTexture>)texture {
   self = [super init];

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

@@ -37,8 +37,7 @@
     StartFrame();
     // If the backing store is for the first layer, return the MTLTexture for the
     // FlutterView.
-    FlutterMetalRenderBackingStore* backingStore =
-        reinterpret_cast<FlutterMetalRenderBackingStore*>([view backingStoreForSize:size]);
+    FlutterRenderBackingStore* backingStore = [view backingStoreForSize:size];
     backing_store_out->metal.texture.texture =
         (__bridge FlutterMetalTextureHandle)backingStore.texture;
   } else {

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

@@ -43,8 +43,7 @@ - (nullable FlutterView*)getView:(uint64_t)viewId {
 
 id<FlutterViewProvider> MockViewProvider() {
   FlutterView* viewMock = OCMClassMock([FlutterView class]);
-  FlutterMetalRenderBackingStore* backingStoreMock =
-      OCMClassMock([FlutterMetalRenderBackingStore class]);
+  FlutterRenderBackingStore* backingStoreMock = OCMClassMock([FlutterRenderBackingStore class]);
   __block id<MTLTexture> textureMock = OCMProtocolMock(@protocol(MTLTexture));
   OCMStub([backingStoreMock texture]).andReturn(textureMock);
 

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

@@ -95,8 +95,7 @@ - (FlutterMetalTexture)createTextureForView:(uint64_t)viewId size:(CGSize)size {
     // FlutterMetalTexture has texture `null`, therefore is discarded.
     return FlutterMetalTexture{};
   }
-  FlutterMetalRenderBackingStore* backingStore =
-      (FlutterMetalRenderBackingStore*)[view backingStoreForSize:size];
+  FlutterRenderBackingStore* backingStore = [view backingStoreForSize:size];
   id<MTLTexture> texture = backingStore.texture;
   FlutterMetalTexture embedderTexture;
   embedderTexture.struct_size = sizeof(FlutterMetalTexture);

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

@@ -10,10 +10,16 @@
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterResizeSynchronizer.h"
 
 /**
- * Represents a buffer that can be resized.
+ * Provides resizable buffers backed by a MTLTexture.
  */
-@protocol FlutterResizableBackingStoreProvider <FlutterResizeSynchronizerDelegate>
+@interface FlutterResizableBackingStoreProvider : NSObject <FlutterResizeSynchronizerDelegate>
 
+/**
+ * Creates a resizable backing store provider for the given CAMetalLayer.
+ */
+- (nonnull instancetype)initWithDevice:(nonnull id<MTLDevice>)device
+                          commandQueue:(nonnull id<MTLCommandQueue>)commandQueue
+                                 layer:(nonnull CALayer*)layer;
 /**
  * Notify of the required backing store size updates. Called during window resize.
  */
@@ -25,19 +31,3 @@
 - (nonnull FlutterRenderBackingStore*)backingStore;
 
 @end
-
-/**
- * Metal-backed FlutterResizableBackingStoreProvider. Backing store in this context implies a
- * MTLTexture.
- */
-@interface FlutterMetalResizableBackingStoreProvider
-    : NSObject <FlutterResizableBackingStoreProvider>
-
-/**
- * Creates a resizable backing store provider for the given CAMetalLayer.
- */
-- (nonnull instancetype)initWithDevice:(nonnull id<MTLDevice>)device
-                          commandQueue:(nonnull id<MTLCommandQueue>)commandQueue
-                                 layer:(nonnull CALayer*)layer;
-
-@end

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

@@ -8,7 +8,7 @@
 
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterSurfaceManager.h"
 
-@implementation FlutterMetalResizableBackingStoreProvider {
+@implementation FlutterResizableBackingStoreProvider {
   id<MTLDevice> _device;
   id<MTLCommandQueue> _commandQueue;
   FlutterSurfaceManager* _surfaceManager;

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

@@ -143,7 +143,7 @@ - (void)cancelIdle {
 - (nonnull FlutterRenderBackingStore*)renderBuffer {
   [self ensureBackBuffer];
   id<MTLTexture> texture = _textures[kFlutterSurfaceManagerBackBuffer];
-  return [[FlutterMetalRenderBackingStore alloc] initWithTexture:texture];
+  return [[FlutterRenderBackingStore alloc] initWithTexture:texture];
 }
 
 - (id<MTLTexture>)createTextureForSurface:(FlutterIOSurfaceHolder*)surface size:(CGSize)size {

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

@@ -43,8 +43,7 @@ - (instancetype)init {
   FlutterSurfaceManager* surfaceManager = CreateSurfaceManager();
   CGSize size = CGSizeMake(100, 50);
   [surfaceManager ensureSurfaceSize:size];
-  id<MTLTexture> texture =
-      (reinterpret_cast<FlutterMetalRenderBackingStore*>([surfaceManager renderBuffer])).texture;
+  id<MTLTexture> texture = [surfaceManager renderBuffer].texture;
   CGSize textureSize = CGSizeMake(texture.width, texture.height);
   ASSERT_TRUE(CGSizeEqualToSize(size, textureSize));
 }
@@ -55,8 +54,7 @@ - (instancetype)init {
   [surfaceManager ensureSurfaceSize:size];
   [surfaceManager renderBuffer];  // make sure we have back buffer
   [surfaceManager swapBuffers];
-  id<MTLTexture> texture =
-      (reinterpret_cast<FlutterMetalRenderBackingStore*>([surfaceManager renderBuffer])).texture;
+  id<MTLTexture> texture = [surfaceManager renderBuffer].texture;
   CGSize textureSize = CGSizeMake(texture.width, texture.height);
   ASSERT_TRUE(CGSizeEqualToSize(size, textureSize));
 }

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

@@ -12,7 +12,7 @@
 @interface FlutterView () {
   __weak id<FlutterViewReshapeListener> _reshapeListener;
   FlutterResizeSynchronizer* _resizeSynchronizer;
-  id<FlutterResizableBackingStoreProvider> _resizableBackingStoreProvider;
+  FlutterResizableBackingStoreProvider* _resizableBackingStoreProvider;
 }
 
 @end
@@ -29,9 +29,9 @@ - (instancetype)initWithMTLDevice:(id<MTLDevice>)device
     [self setLayerContentsRedrawPolicy:NSViewLayerContentsRedrawDuringViewResize];
     _reshapeListener = reshapeListener;
     _resizableBackingStoreProvider =
-        [[FlutterMetalResizableBackingStoreProvider alloc] initWithDevice:device
-                                                             commandQueue:commandQueue
-                                                                    layer:self.layer];
+        [[FlutterResizableBackingStoreProvider alloc] initWithDevice:device
+                                                        commandQueue:commandQueue
+                                                               layer:self.layer];
     _resizeSynchronizer =
         [[FlutterResizeSynchronizer alloc] initWithDelegate:_resizableBackingStoreProvider];
   }