Extract backend-specific code in ShellTestPlatformView (flutter/engine#56722)

Moves code specific to each graphics backend into the (existing) translation unit associated with that backend.

Previously, we could not include any Objective-C types in `shell_test_platform_view_metal.h`, since that file was included into `shell_test_platform_view.cc`, which is pure C++. To work around this, we had encapsulated Objective-C Metal types in a `DarwinContextMetal` struct hidden in the implementation file with a pointer to it forward-declared in the header.

We now use Metal types directly in the header, without the workarounds.

Issue: https://github.com/flutter/flutter/issues/158998
Issue: https://github.com/flutter/flutter/issues/137801

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

engine/src/flutter/shell/common/shell_test_platform_view.cc

@@ -4,20 +4,11 @@
 
 #include "flutter/shell/common/shell_test_platform_view.h"
 
-#ifdef SHELL_ENABLE_GL
-#include "flutter/shell/common/shell_test_platform_view_gl.h"
-#endif  // SHELL_ENABLE_GL
-#ifdef SHELL_ENABLE_VULKAN
-#include "flutter/shell/common/shell_test_platform_view_vulkan.h"
-#endif  // SHELL_ENABLE_VULKAN
-#ifdef SHELL_ENABLE_METAL
-#include "flutter/shell/common/shell_test_platform_view_metal.h"
-#endif  // SHELL_ENABLE_METAL
+#include <memory>
 
 #include "flutter/shell/common/vsync_waiter_fallback.h"
 
-namespace flutter {
-namespace testing {
+namespace flutter::testing {
 
 std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::Create(
     BackendType backend,
@@ -32,35 +23,60 @@ std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::Create(
   // Make this fully runtime configurable
   switch (backend) {
     case BackendType::kGLBackend:
-#ifdef SHELL_ENABLE_GL
-      return std::make_unique<ShellTestPlatformViewGL>(
-          delegate, task_runners, vsync_clock, create_vsync_waiter,
-          shell_test_external_view_embedder);
-#else
-      FML_LOG(FATAL) << "OpenGL not enabled in this build";
-      return nullptr;
-#endif  // SHELL_ENABLE_GL
-    case BackendType::kVulkanBackend:
-#ifdef SHELL_ENABLE_VULKAN
-      return std::make_unique<ShellTestPlatformViewVulkan>(
-          delegate, task_runners, vsync_clock, create_vsync_waiter,
-          shell_test_external_view_embedder);
-#else
-      FML_LOG(FATAL) << "Vulkan not enabled in this build";
-      return nullptr;
-#endif  // SHELL_ENABLE_VULKAN
+      return CreateGL(delegate, task_runners, vsync_clock, create_vsync_waiter,
+                      shell_test_external_view_embedder,
+                      is_gpu_disabled_sync_switch);
     case BackendType::kMetalBackend:
-#ifdef SHELL_ENABLE_METAL
-      return std::make_unique<ShellTestPlatformViewMetal>(
+      return CreateMetal(delegate, task_runners, vsync_clock,
+                         create_vsync_waiter, shell_test_external_view_embedder,
+                         is_gpu_disabled_sync_switch);
+    case BackendType::kVulkanBackend:
+      return CreateVulkan(
           delegate, task_runners, vsync_clock, create_vsync_waiter,
           shell_test_external_view_embedder, is_gpu_disabled_sync_switch);
-#else
-      FML_LOG(FATAL) << "Metal not enabled in this build";
-      return nullptr;
-#endif  // SHELL_ENABLE_METAL
   }
 }
 
+#ifndef SHELL_ENABLE_GL
+std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::CreateGL(
+    PlatformView::Delegate& delegate,
+    const TaskRunners& task_runners,
+    const std::shared_ptr<ShellTestVsyncClock>& vsync_clock,
+    const CreateVsyncWaiter& create_vsync_waiter,
+    const std::shared_ptr<ShellTestExternalViewEmbedder>&
+        shell_test_external_view_embedder,
+    const std::shared_ptr<const fml::SyncSwitch>& is_gpu_disabled_sync_switch) {
+  FML_LOG(FATAL) << "OpenGL backend not enabled in this build";
+  return nullptr;
+}
+#endif  // SHELL_ENABLE_GL
+#ifndef SHELL_ENABLE_METAL
+std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::CreateMetal(
+    PlatformView::Delegate& delegate,
+    const TaskRunners& task_runners,
+    const std::shared_ptr<ShellTestVsyncClock>& vsync_clock,
+    const CreateVsyncWaiter& create_vsync_waiter,
+    const std::shared_ptr<ShellTestExternalViewEmbedder>&
+        shell_test_external_view_embedder,
+    const std::shared_ptr<const fml::SyncSwitch>& is_gpu_disabled_sync_switch) {
+  FML_LOG(FATAL) << "Metal backend not enabled in this build";
+  return nullptr;
+}
+#endif  // SHELL_ENABLE_METAL
+#ifndef SHELL_ENABLE_VULKAN
+std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::CreateVulkan(
+    PlatformView::Delegate& delegate,
+    const TaskRunners& task_runners,
+    const std::shared_ptr<ShellTestVsyncClock>& vsync_clock,
+    const CreateVsyncWaiter& create_vsync_waiter,
+    const std::shared_ptr<ShellTestExternalViewEmbedder>&
+        shell_test_external_view_embedder,
+    const std::shared_ptr<const fml::SyncSwitch>& is_gpu_disabled_sync_switch) {
+  FML_LOG(FATAL) << "Vulkan backend not enabled in this build";
+  return nullptr;
+}
+#endif  // SHELL_ENABLE_VULKAN
+
 ShellTestPlatformViewBuilder::ShellTestPlatformViewBuilder(Config config)
     : config_(std::move(config)) {}
 
@@ -90,5 +106,4 @@ std::unique_ptr<PlatformView> ShellTestPlatformViewBuilder::operator()(
   );
 }
 
-}  // namespace testing
-}  // namespace flutter
+}  // namespace flutter::testing

engine/src/flutter/shell/common/shell_test_platform_view.h

@@ -11,8 +11,7 @@
 #include "flutter/shell/common/shell_test_external_view_embedder.h"
 #include "flutter/shell/common/vsync_waiters_test.h"
 
-namespace flutter {
-namespace testing {
+namespace flutter::testing {
 
 class ShellTestPlatformView : public PlatformView {
  public:
@@ -53,6 +52,34 @@ class ShellTestPlatformView : public PlatformView {
                         const TaskRunners& task_runners)
       : PlatformView(delegate, task_runners) {}
 
+  static std::unique_ptr<ShellTestPlatformView> CreateGL(
+      PlatformView::Delegate& delegate,
+      const TaskRunners& task_runners,
+      const std::shared_ptr<ShellTestVsyncClock>& vsync_clock,
+      const CreateVsyncWaiter& create_vsync_waiter,
+      const std::shared_ptr<ShellTestExternalViewEmbedder>&
+          shell_test_external_view_embedder,
+      const std::shared_ptr<const fml::SyncSwitch>&
+          is_gpu_disabled_sync_switch);
+  static std::unique_ptr<ShellTestPlatformView> CreateMetal(
+      PlatformView::Delegate& delegate,
+      const TaskRunners& task_runners,
+      const std::shared_ptr<ShellTestVsyncClock>& vsync_clock,
+      const CreateVsyncWaiter& create_vsync_waiter,
+      const std::shared_ptr<ShellTestExternalViewEmbedder>&
+          shell_test_external_view_embedder,
+      const std::shared_ptr<const fml::SyncSwitch>&
+          is_gpu_disabled_sync_switch);
+  static std::unique_ptr<ShellTestPlatformView> CreateVulkan(
+      PlatformView::Delegate& delegate,
+      const TaskRunners& task_runners,
+      const std::shared_ptr<ShellTestVsyncClock>& vsync_clock,
+      const CreateVsyncWaiter& create_vsync_waiter,
+      const std::shared_ptr<ShellTestExternalViewEmbedder>&
+          shell_test_external_view_embedder,
+      const std::shared_ptr<const fml::SyncSwitch>&
+          is_gpu_disabled_sync_switch);
+
   FML_DISALLOW_COPY_AND_ASSIGN(ShellTestPlatformView);
 };
 
@@ -77,7 +104,6 @@ class ShellTestPlatformViewBuilder {
   Config config_;
 };
 
-}  // namespace testing
-}  // namespace flutter
+}  // namespace flutter::testing
 
 #endif  // FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_H_

engine/src/flutter/shell/common/shell_test_platform_view_gl.cc

@@ -22,6 +22,19 @@ static std::vector<std::shared_ptr<fml::Mapping>> ShaderLibraryMappings() {
   };
 }
 
+std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::CreateGL(
+    PlatformView::Delegate& delegate,
+    const TaskRunners& task_runners,
+    const std::shared_ptr<ShellTestVsyncClock>& vsync_clock,
+    const CreateVsyncWaiter& create_vsync_waiter,
+    const std::shared_ptr<ShellTestExternalViewEmbedder>&
+        shell_test_external_view_embedder,
+    const std::shared_ptr<const fml::SyncSwitch>& is_gpu_disabled_sync_switch) {
+  return std::make_unique<ShellTestPlatformViewGL>(
+      delegate, task_runners, vsync_clock, create_vsync_waiter,
+      shell_test_external_view_embedder);
+}
+
 ShellTestPlatformViewGL::ShellTestPlatformViewGL(
     PlatformView::Delegate& delegate,
     const TaskRunners& task_runners,

engine/src/flutter/shell/common/shell_test_platform_view_metal.h

@@ -5,14 +5,16 @@
 #ifndef FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_METAL_H_
 #define FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_METAL_H_
 
-#include "flutter/fml/macros.h"
 #include "flutter/shell/common/shell_test_platform_view.h"
+
+#import <Metal/Metal.h>
+
+#include "flutter/fml/macros.h"
 #include "flutter/shell/gpu/gpu_surface_metal_delegate.h"
+#include "flutter/shell/platform/darwin/graphics/FlutterDarwinContextMetalImpeller.h"
+#include "flutter/shell/platform/darwin/graphics/FlutterDarwinContextMetalSkia.h"
 
-namespace flutter {
-namespace testing {
-
-struct DarwinContextMetal;
+namespace flutter::testing {
 
 class ShellTestPlatformViewMetal final : public ShellTestPlatformView,
                                          public GPUSurfaceMetalDelegate {
@@ -30,7 +32,9 @@ class ShellTestPlatformViewMetal final : public ShellTestPlatformView,
   virtual ~ShellTestPlatformViewMetal() override;
 
  private:
-  const std::unique_ptr<DarwinContextMetal> metal_context_;
+  FlutterDarwinContextMetalSkia* skia_context_;
+  FlutterDarwinContextMetalImpeller* impeller_context_;
+  id<MTLTexture> offscreen_texture_;
   const CreateVsyncWaiter create_vsync_waiter_;
   const std::shared_ptr<ShellTestVsyncClock> vsync_clock_;
   const std::shared_ptr<ShellTestExternalViewEmbedder>
@@ -70,7 +74,6 @@ class ShellTestPlatformViewMetal final : public ShellTestPlatformView,
   FML_DISALLOW_COPY_AND_ASSIGN(ShellTestPlatformViewMetal);
 };
 
-}  // namespace testing
-}  // namespace flutter
+}  // namespace flutter::testing
 
 #endif  // FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_METAL_H_

engine/src/flutter/shell/common/shell_test_platform_view_metal.mm

@@ -4,52 +4,25 @@
 
 #include "flutter/shell/common/shell_test_platform_view_metal.h"
 
-#import <Metal/Metal.h>
-
 #include <utility>
 
 #include "flutter/shell/gpu/gpu_surface_metal_impeller.h"
 #include "flutter/shell/gpu/gpu_surface_metal_skia.h"
-#include "flutter/shell/platform/darwin/graphics/FlutterDarwinContextMetalImpeller.h"
-#include "flutter/shell/platform/darwin/graphics/FlutterDarwinContextMetalSkia.h"
 
 FLUTTER_ASSERT_ARC
 
-namespace flutter {
-namespace testing {
+namespace flutter::testing {
 
-// This is out of the header so that shell_test_platform_view_metal.h can be included in
-// non-Objective-C TUs.
-struct DarwinContextMetal {
-  FlutterDarwinContextMetalSkia* skia_context;
-  FlutterDarwinContextMetalImpeller* impeller_context;
-  id<MTLTexture> offscreen_texture;
-};
-
-static std::unique_ptr<DarwinContextMetal> CreateDarwinContext(
-    bool impeller,
+std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::CreateMetal(
+    PlatformView::Delegate& delegate,
+    const TaskRunners& task_runners,
+    const std::shared_ptr<ShellTestVsyncClock>& vsync_clock,
+    const CreateVsyncWaiter& create_vsync_waiter,
+    const std::shared_ptr<ShellTestExternalViewEmbedder>& shell_test_external_view_embedder,
     const std::shared_ptr<const fml::SyncSwitch>& is_gpu_disabled_sync_switch) {
-  FlutterDarwinContextMetalSkia* skia_context = nil;
-  FlutterDarwinContextMetalImpeller* impeller_context = nil;
-  id<MTLDevice> device = nil;
-  if (impeller) {
-    impeller_context = [[FlutterDarwinContextMetalImpeller alloc] init:is_gpu_disabled_sync_switch];
-    FML_CHECK(impeller_context.context);
-    device = impeller_context.context->GetMTLDevice();
-  } else {
-    skia_context = [[FlutterDarwinContextMetalSkia alloc] initWithDefaultMTLDevice];
-    FML_CHECK(skia_context.mainContext);
-    device = skia_context.device;
-  }
-  auto descriptor =
-      [MTLTextureDescriptor texture2DDescriptorWithPixelFormat:MTLPixelFormatBGRA8Unorm
-                                                         width:800
-                                                        height:600
-                                                     mipmapped:NO];
-  descriptor.usage = MTLTextureUsageRenderTarget | MTLTextureUsageShaderRead;
-  id<MTLTexture> offscreen_texture = [device newTextureWithDescriptor:descriptor];
-  return std::make_unique<DarwinContextMetal>(
-      DarwinContextMetal{skia_context, impeller_context, offscreen_texture});
+  return std::make_unique<ShellTestPlatformViewMetal>(
+      delegate, task_runners, vsync_clock, create_vsync_waiter, shell_test_external_view_embedder,
+      is_gpu_disabled_sync_switch);
 }
 
 ShellTestPlatformViewMetal::ShellTestPlatformViewMetal(
@@ -61,11 +34,28 @@ ShellTestPlatformViewMetal::ShellTestPlatformViewMetal(
     const std::shared_ptr<const fml::SyncSwitch>& is_gpu_disabled_sync_switch)
     : ShellTestPlatformView(delegate, task_runners),
       GPUSurfaceMetalDelegate(MTLRenderTargetType::kMTLTexture),
-      metal_context_(
-          CreateDarwinContext(GetSettings().enable_impeller, is_gpu_disabled_sync_switch)),
       create_vsync_waiter_(std::move(create_vsync_waiter)),
       vsync_clock_(std::move(vsync_clock)),
-      shell_test_external_view_embedder_(std::move(shell_test_external_view_embedder)) {}
+      shell_test_external_view_embedder_(std::move(shell_test_external_view_embedder)) {
+  id<MTLDevice> device = nil;
+  if (GetSettings().enable_impeller) {
+    impeller_context_ =
+        [[FlutterDarwinContextMetalImpeller alloc] init:is_gpu_disabled_sync_switch];
+    FML_CHECK(impeller_context_.context);
+    device = impeller_context_.context->GetMTLDevice();
+  } else {
+    skia_context_ = [[FlutterDarwinContextMetalSkia alloc] initWithDefaultMTLDevice];
+    FML_CHECK(skia_context_.mainContext);
+    device = skia_context_.device;
+  }
+  auto descriptor =
+      [MTLTextureDescriptor texture2DDescriptorWithPixelFormat:MTLPixelFormatBGRA8Unorm
+                                                         width:800
+                                                        height:600
+                                                     mipmapped:NO];
+  descriptor.usage = MTLTextureUsageRenderTarget | MTLTextureUsageShaderRead;
+  offscreen_texture_ = [device newTextureWithDescriptor:descriptor];
+}
 
 ShellTestPlatformViewMetal::~ShellTestPlatformViewMetal() = default;
 
@@ -93,16 +83,16 @@ PointerDataDispatcherMaker ShellTestPlatformViewMetal::GetDispatcherMaker() {
 // |PlatformView|
 std::unique_ptr<Surface> ShellTestPlatformViewMetal::CreateRenderingSurface() {
   if (GetSettings().enable_impeller) {
-    auto context = metal_context_->impeller_context.context;
+    auto context = impeller_context_.context;
     return std::make_unique<GPUSurfaceMetalImpeller>(
         this, std::make_shared<impeller::AiksContext>(context, nullptr));
   }
-  return std::make_unique<GPUSurfaceMetalSkia>(this, metal_context_->skia_context.mainContext);
+  return std::make_unique<GPUSurfaceMetalSkia>(this, skia_context_.mainContext);
 }
 
 // |PlatformView|
 std::shared_ptr<impeller::Context> ShellTestPlatformViewMetal::GetImpellerContext() const {
-  return metal_context_->impeller_context.context;
+  return impeller_context_.context;
 }
 
 // |GPUSurfaceMetalDelegate|
@@ -123,7 +113,7 @@ bool ShellTestPlatformViewMetal::PresentDrawable(GrMTLHandle drawable) const {
 GPUMTLTextureInfo ShellTestPlatformViewMetal::GetMTLTexture(const SkISize& frame_info) const {
   return {
       .texture_id = 0,
-      .texture = (__bridge GPUMTLTextureHandle)metal_context_->offscreen_texture,
+      .texture = (__bridge GPUMTLTextureHandle)offscreen_texture_,
   };
 }
 
@@ -133,5 +123,4 @@ bool ShellTestPlatformViewMetal::PresentTexture(GPUMTLTextureInfo texture) const
   return true;
 }
 
-}  // namespace testing
-}  // namespace flutter
+}  // namespace flutter::testing

engine/src/flutter/shell/common/shell_test_platform_view_vulkan.cc

@@ -23,8 +23,20 @@
 #include "flutter/vulkan/swiftshader_path.h"
 #endif
 
-namespace flutter {
-namespace testing {
+namespace flutter::testing {
+
+std::unique_ptr<ShellTestPlatformView> ShellTestPlatformView::CreateVulkan(
+    PlatformView::Delegate& delegate,
+    const TaskRunners& task_runners,
+    const std::shared_ptr<ShellTestVsyncClock>& vsync_clock,
+    const CreateVsyncWaiter& create_vsync_waiter,
+    const std::shared_ptr<ShellTestExternalViewEmbedder>&
+        shell_test_external_view_embedder,
+    const std::shared_ptr<const fml::SyncSwitch>& is_gpu_disabled_sync_switch) {
+  return std::make_unique<ShellTestPlatformViewVulkan>(
+      delegate, task_runners, vsync_clock, create_vsync_waiter,
+      shell_test_external_view_embedder);
+}
 
 ShellTestPlatformViewVulkan::ShellTestPlatformViewVulkan(
     PlatformView::Delegate& delegate,
@@ -232,5 +244,4 @@ SkMatrix ShellTestPlatformViewVulkan::OffScreenSurface::GetRootTransformation()
   return matrix;
 }
 
-}  // namespace testing
-}  // namespace flutter
+}  // namespace flutter::testing

engine/src/flutter/shell/common/shell_test_platform_view_vulkan.h

@@ -15,8 +15,7 @@
 #include "third_party/skia/include/gpu/vk/VulkanMemoryAllocator.h"
 #include "third_party/skia/include/gpu/vk/VulkanTypes.h"
 
-namespace flutter {
-namespace testing {
+namespace flutter::testing {
 
 class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
  public:
@@ -93,7 +92,6 @@ class ShellTestPlatformViewVulkan : public ShellTestPlatformView {
   FML_DISALLOW_COPY_AND_ASSIGN(ShellTestPlatformViewVulkan);
 };
 
-}  // namespace testing
-}  // namespace flutter
+}  // namespace flutter::testing
 
 #endif  // FLUTTER_SHELL_COMMON_SHELL_TEST_PLATFORM_VIEW_VULKAN_H_