[Flutter GPU] Add support for drawing Flutter GPU textures in the playground.

impeller/fixtures/dart_tests.dart

@@ -13,6 +13,10 @@ void sayHi() {
   print('Hi');
 }
 
+/// Pass a texture back to the playground for rendering to the surface.
+@pragma('vm:external-name', 'SetDisplayTexture')
+external void setDisplayTexture(gpu.Texture texture);
+
 @pragma('vm:entry-point')
 void instantiateDefaultContext() {
   // ignore: unused_local_variable
@@ -102,9 +106,9 @@ ByteData float32(List<double> values) {
 }
 
 @pragma('vm:entry-point')
-void canCreateRenderPassAndSubmit() {
-  final gpu.Texture? renderTexture =
-      gpu.gpuContext.createTexture(gpu.StorageMode.devicePrivate, 100, 100);
+void canCreateRenderPassAndSubmit(int width, int height) {
+  final gpu.Texture? renderTexture = gpu.gpuContext
+      .createTexture(gpu.StorageMode.devicePrivate, width, height);
   assert(renderTexture != null);
 
   final gpu.CommandBuffer commandBuffer = gpu.gpuContext.createCommandBuffer();
@@ -123,9 +127,9 @@ void canCreateRenderPassAndSubmit() {
 
   final gpu.HostBuffer transients = gpu.gpuContext.createHostBuffer();
   final gpu.BufferView vertices = transients.emplace(float32(<double>[
-    -0.5, -0.5, //
+    -0.5, 0.5, //
+    0.0, -0.5, //
     0.5, 0.5, //
-    0.5, -0.5, //
   ]));
   final gpu.BufferView vertInfoData = transients.emplace(float32(<double>[
     1, 0, 0, 0, // mvp
@@ -142,4 +146,6 @@ void canCreateRenderPassAndSubmit() {
   encoder.draw();
 
   commandBuffer.submit();
+
+  setDisplayTexture(renderTexture);
 }

impeller/playground/playground.cc

@@ -148,6 +148,10 @@ void Playground::SetupWindow() {
   start_time_ = fml::TimePoint::Now().ToEpochDelta();
 }
 
+bool Playground::IsPlaygroundEnabled() const {
+  return switches_.enable_playground;
+}
+
 void Playground::TeardownWindow() {
   if (context_) {
     context_->Shutdown();

impeller/playground/playground.h

@@ -64,6 +64,8 @@ class Playground {
 
   void TeardownWindow();
 
+  bool IsPlaygroundEnabled() const;
+
   Point GetCursorPosition() const;
 
   ISize GetWindowSize() const;

impeller/renderer/renderer_dart_unittests.cc

@@ -10,14 +10,20 @@
 #include "flutter/common/task_runners.h"
 #include "flutter/lib/gpu/context.h"
 #include "flutter/lib/gpu/shader_library.h"
+#include "flutter/lib/gpu/texture.h"
 #include "flutter/runtime/dart_isolate.h"
 #include "flutter/runtime/dart_vm_lifecycle.h"
 #include "flutter/testing/dart_fixture.h"
 #include "flutter/testing/dart_isolate_runner.h"
+#include "flutter/testing/test_dart_native_resolver.h"
 #include "flutter/testing/testing.h"
 #include "fml/memory/ref_ptr.h"
+#include "impeller/fixtures/texture.frag.h"
+#include "impeller/fixtures/texture.vert.h"
 #include "impeller/playground/playground_test.h"
+#include "impeller/renderer/pipeline_library.h"
 #include "impeller/renderer/render_pass.h"
+#include "impeller/renderer/vertex_buffer_builder.h"
 
 #include "gtest/gtest.h"
 #include "third_party/imgui/imgui.h"
@@ -46,6 +52,23 @@ class RendererDartTest : public PlaygroundTest,
     isolate_ = CreateDartIsolate();
     assert(isolate_);
     assert(isolate_->get()->GetPhase() == flutter::DartIsolate::Phase::Running);
+
+    // Set up native callbacks.
+    //
+    // Note: The Dart isolate is configured (by
+    //       `RendererDartTest::CreateDartIsolate`) to use the main thread, so
+    //       there's no need for additional synchronization.
+    {
+      auto set_display_texture = [this](Dart_NativeArguments args) {
+        flutter::gpu::Texture* texture =
+            tonic::DartConverter<flutter::gpu::Texture*>::FromDart(
+                Dart_GetNativeArgument(args, 0));
+        assert(texture != nullptr);  // Should always be a valid pointer.
+        received_texture_ = texture->GetTexture();
+      };
+      AddNativeCallback("SetDisplayTexture",
+                        CREATE_NATIVE_ENTRY(set_display_texture));
+    }
   }
 
   flutter::testing::AutoIsolateShutdown* GetIsolate() {
@@ -58,6 +81,169 @@ class RendererDartTest : public PlaygroundTest,
     return isolate_.get();
   }
 
+  /// @brief  Run a Dart function that's expected to create a texture and pass
+  ///         it back for rendering via `drawToPlayground`.
+  std::shared_ptr<Texture> GetRenderedTextureFromDart(
+      const char* dart_function_name) {
+    bool success =
+        GetIsolate()->RunInIsolateScope([this, &dart_function_name]() -> bool {
+          Dart_Handle args[] = {tonic::ToDart(GetWindowSize().width),
+                                tonic::ToDart(GetWindowSize().height)};
+          if (tonic::CheckAndHandleError(
+                  ::Dart_Invoke(Dart_RootLibrary(),
+                                tonic::ToDart(dart_function_name), 2, args))) {
+            return false;
+          }
+          return true;
+        });
+    if (!success) {
+      FML_LOG(ERROR) << "Failed to invoke dart test function:"
+                     << dart_function_name;
+      return nullptr;
+    }
+    if (!received_texture_) {
+      FML_LOG(ERROR) << "Dart test function `" << dart_function_name
+                     << "` did not invoke `drawToPlaygroundSurface`.";
+      return nullptr;
+    }
+    return received_texture_;
+  }
+
+  /// @brief  Invokes a Dart function.
+  ///
+  ///         Returns false if invoking the function failed or if any unhandled
+  ///         exceptions were thrown.
+  bool RunDartFunction(const char* dart_function_name) {
+    return GetIsolate()->RunInIsolateScope([&dart_function_name]() -> bool {
+      if (tonic::CheckAndHandleError(
+              ::Dart_Invoke(Dart_RootLibrary(),
+                            tonic::ToDart(dart_function_name), 0, nullptr))) {
+        return false;
+      }
+      return true;
+    });
+  }
+
+  /// @brief  Invokes a Dart function with the window's width and height as
+  ///         arguments.
+  ///
+  ///         Returns false if invoking the function failed or if any unhandled
+  ///         exceptions were thrown.
+  bool RunDartFunctionWithWindowSize(const char* dart_function_name) {
+    return GetIsolate()->RunInIsolateScope(
+        [this, &dart_function_name]() -> bool {
+          Dart_Handle args[] = {tonic::ToDart(GetWindowSize().width),
+                                tonic::ToDart(GetWindowSize().height)};
+          if (tonic::CheckAndHandleError(
+                  ::Dart_Invoke(Dart_RootLibrary(),
+                                tonic::ToDart(dart_function_name), 2, args))) {
+            return false;
+          }
+          return true;
+        });
+  }
+
+  /// @brief  Call a dart function that produces a texture and render the result
+  ///         in the playground.
+  ///
+  ///         If the playground isn't enabled, the function is simply run once
+  ///         in order to verify that it doesn't throw any unhandled exceptions.
+  bool RenderDartToPlayground(const char* dart_function_name) {
+    if (!IsPlaygroundEnabled()) {
+      // If the playground is not enabled, run the function instead to at least
+      // verify that it doesn't crash.
+      return RunDartFunctionWithWindowSize(dart_function_name);
+    }
+
+    auto context = GetContext();
+    assert(context != nullptr);
+
+    //------------------------------------------------------------------------------
+    /// Prepare pipeline.
+    ///
+
+    using TextureVS = TextureVertexShader;
+    using TextureFS = TextureFragmentShader;
+    using TexturePipelineBuilder = PipelineBuilder<TextureVS, TextureFS>;
+
+    auto pipeline_desc =
+        TexturePipelineBuilder::MakeDefaultPipelineDescriptor(*context);
+    if (!pipeline_desc.has_value()) {
+      FML_LOG(ERROR) << "Failed to create default pipeline descriptor.";
+      return false;
+    }
+    pipeline_desc->SetSampleCount(SampleCount::kCount4);
+    pipeline_desc->SetStencilAttachmentDescriptors(std::nullopt);
+    pipeline_desc->SetDepthStencilAttachmentDescriptor(std::nullopt);
+    pipeline_desc->SetStencilPixelFormat(PixelFormat::kUnknown);
+    pipeline_desc->SetDepthPixelFormat(PixelFormat::kUnknown);
+
+    auto pipeline =
+        context->GetPipelineLibrary()->GetPipeline(pipeline_desc).Get();
+    if (!pipeline || !pipeline->IsValid()) {
+      FML_LOG(ERROR) << "Failed to create default pipeline.";
+      return false;
+    }
+
+    //------------------------------------------------------------------------------
+    /// Prepare vertex data.
+    ///
+
+    VertexBufferBuilder<TextureVS::PerVertexData> texture_vtx_builder;
+
+    // Always stretch out the texture to fill the screen.
+
+    // clang-format off
+    texture_vtx_builder.AddVertices({
+        {{-0.5, -0.5, 0.0}, {0.0, 0.0}},  // 1
+        {{ 0.5, -0.5, 0.0}, {1.0, 0.0}},  // 2
+        {{ 0.5,  0.5, 0.0}, {1.0, 1.0}},  // 3
+        {{-0.5, -0.5, 0.0}, {0.0, 0.0}},  // 1
+        {{ 0.5,  0.5, 0.0}, {1.0, 1.0}},  // 3
+        {{-0.5,  0.5, 0.0}, {0.0, 1.0}},  // 4
+    });
+    // clang-format on
+
+    //------------------------------------------------------------------------------
+    /// Prepare sampler.
+    ///
+
+    const auto& sampler = context->GetSamplerLibrary()->GetSampler({});
+    if (!sampler) {
+      FML_LOG(ERROR) << "Failed to create default sampler.";
+      return false;
+    }
+
+    //------------------------------------------------------------------------------
+    /// Render to playground.
+    ///
+
+    SinglePassCallback callback = [&](RenderPass& pass) {
+      auto texture = GetRenderedTextureFromDart(dart_function_name);
+      if (!texture) {
+        return false;
+      }
+
+      auto buffer = HostBuffer::Create(context->GetResourceAllocator());
+
+      pass.SetVertexBuffer(texture_vtx_builder.CreateVertexBuffer(
+          *context->GetResourceAllocator()));
+
+      TextureVS::UniformBuffer uniforms;
+      uniforms.mvp = Matrix();
+      TextureVS::BindUniformBuffer(pass, buffer->EmplaceUniform(uniforms));
+      TextureFS::BindTextureContents(pass, texture, sampler);
+
+      pass.SetPipeline(pipeline);
+
+      if (!pass.Draw().ok()) {
+        return false;
+      }
+      return true;
+    };
+    return OpenPlaygroundHere(callback);
+  }
+
  private:
   std::unique_ptr<flutter::testing::AutoIsolateShutdown> CreateDartIsolate() {
     const auto settings = CreateSettingsForFixture();
@@ -76,65 +262,46 @@ class RendererDartTest : public PlaygroundTest,
   flutter::DartVMRef vm_ref_;
   fml::RefPtr<fml::TaskRunner> current_task_runner_;
   std::unique_ptr<flutter::testing::AutoIsolateShutdown> isolate_;
+
+  std::shared_ptr<Texture> received_texture_;
 };
 
 INSTANTIATE_PLAYGROUND_SUITE(RendererDartTest);
 
 TEST_P(RendererDartTest, CanRunDartInPlaygroundFrame) {
-  auto isolate = GetIsolate();
-
   SinglePassCallback callback = [&](RenderPass& pass) {
     ImGui::Begin("Dart test", nullptr);
     ImGui::Text(
         "This test executes Dart code during the playground frame callback.");
     ImGui::End();
 
-    return isolate->RunInIsolateScope([]() -> bool {
-      if (tonic::CheckAndHandleError(::Dart_Invoke(
-              Dart_RootLibrary(), tonic::ToDart("sayHi"), 0, nullptr))) {
-        return false;
-      }
-      return true;
-    });
+    return RunDartFunction("sayHi");
   };
-  OpenPlaygroundHere(callback);
+  ASSERT_TRUE(OpenPlaygroundHere(callback));
 }
 
-TEST_P(RendererDartTest, CanInstantiateFlutterGPUContext) {
-  auto isolate = GetIsolate();
-  bool result = isolate->RunInIsolateScope([]() -> bool {
-    if (tonic::CheckAndHandleError(::Dart_Invoke(
-            Dart_RootLibrary(), tonic::ToDart("instantiateDefaultContext"), 0,
-            nullptr))) {
-      return false;
-    }
-    return true;
-  });
+/// These test entries correspond to Dart functions located in
+/// `flutter/impeller/fixtures/dart_tests.dart`
 
-  ASSERT_TRUE(result);
+TEST_P(RendererDartTest, CanInstantiateFlutterGPUContext) {
+  ASSERT_TRUE(RunDartFunction("instantiateDefaultContext"));
 }
 
-#define DART_TEST_CASE(name)                                            \
-  TEST_P(RendererDartTest, name) {                                      \
-    auto isolate = GetIsolate();                                        \
-    bool result = isolate->RunInIsolateScope([]() -> bool {             \
-      if (tonic::CheckAndHandleError(::Dart_Invoke(                     \
-              Dart_RootLibrary(), tonic::ToDart(#name), 0, nullptr))) { \
-        return false;                                                   \
-      }                                                                 \
-      return true;                                                      \
-    });                                                                 \
-    ASSERT_TRUE(result);                                                \
-  }
+TEST_P(RendererDartTest, CanCreateShaderLibrary) {
+  ASSERT_TRUE(RunDartFunction("canCreateShaderLibrary"));
+}
 
-/// These test entries correspond to Dart functions located in
-/// `flutter/impeller/fixtures/dart_tests.dart`
+TEST_P(RendererDartTest, CanReflectUniformStructs) {
+  ASSERT_TRUE(RunDartFunction("canReflectUniformStructs"));
+}
 
-DART_TEST_CASE(canCreateShaderLibrary);
-DART_TEST_CASE(canReflectUniformStructs);
-DART_TEST_CASE(uniformBindFailsForInvalidHostBufferOffset);
+TEST_P(RendererDartTest, UniformBindFailsForInvalidHostBufferOffset) {
+  ASSERT_TRUE(RunDartFunction("uniformBindFailsForInvalidHostBufferOffset"));
+}
 
-DART_TEST_CASE(canCreateRenderPassAndSubmit);
+TEST_P(RendererDartTest, CanCreateRenderPassAndSubmit) {
+  ASSERT_TRUE(RenderDartToPlayground("canCreateRenderPassAndSubmit"));
+}
 
 }  // namespace testing
 }  // namespace impeller