[macOS] Merge FlutterBackingStore implementations (#37730)

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

Author: cbracken

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];
   }