[Impeller] Add interface for submitting multiple command buffers at once. (#50139)

The Impeller Vulkan backend benefits from batching submission to the vk graphics queue. Managing this automatically is non-trivial and adds surprising/fragile thread based behavior, see: #49870

Instead, introduce an impeller::CommandQueue object that command buffers must be submitted to in lieu of CommandBuffer->Submit, which has been made private.

TLDR

old
```c++
buffer->Submit();
```

new
```c++
context.GetQueue()->Submit({buffer});
```

The Metal and GLES implementations internally just call the private CommandBuffer->Submit, though there may be future opportunities to simplify here. The Vulkan implementation is where the meat is.

Aiks takes advantage of this by storing all command buffers on the aiks context while rendering a frame, and then performing one submit in aiks_context render. I don't think this will introduce any thread safety problems, as we don't guarantee much about aiks context - nor do we use it in a multithreaded context as far as I know.

Other tasks such as image upload still just directly submit their command buffers via the queue.

Fixes flutter/flutter#141123

Author: Jonah Williams

ci/licenses_golden/licenses_flutter

@@ -5449,6 +5449,8 @@ ORIGIN: ../../../flutter/impeller/renderer/backend/vulkan/command_encoder_vk.cc
 ORIGIN: ../../../flutter/impeller/renderer/backend/vulkan/command_encoder_vk.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/vulkan/command_pool_vk.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/vulkan/command_pool_vk.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/renderer/backend/vulkan/command_queue_vk.cc + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/renderer/backend/vulkan/command_queue_vk.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/vulkan/compute_pass_vk.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/vulkan/compute_pass_vk.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/backend/vulkan/compute_pipeline_vk.cc + ../../../flutter/LICENSE
@@ -5521,6 +5523,8 @@ ORIGIN: ../../../flutter/impeller/renderer/command.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/command.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/command_buffer.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/command_buffer.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/renderer/command_queue.cc + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/renderer/command_queue.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/compute_pass.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/compute_pass.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/renderer/compute_pipeline_builder.cc + ../../../flutter/LICENSE
@@ -8298,6 +8302,8 @@ FILE: ../../../flutter/impeller/renderer/backend/vulkan/command_encoder_vk.cc
 FILE: ../../../flutter/impeller/renderer/backend/vulkan/command_encoder_vk.h
 FILE: ../../../flutter/impeller/renderer/backend/vulkan/command_pool_vk.cc
 FILE: ../../../flutter/impeller/renderer/backend/vulkan/command_pool_vk.h
+FILE: ../../../flutter/impeller/renderer/backend/vulkan/command_queue_vk.cc
+FILE: ../../../flutter/impeller/renderer/backend/vulkan/command_queue_vk.h
 FILE: ../../../flutter/impeller/renderer/backend/vulkan/compute_pass_vk.cc
 FILE: ../../../flutter/impeller/renderer/backend/vulkan/compute_pass_vk.h
 FILE: ../../../flutter/impeller/renderer/backend/vulkan/compute_pipeline_vk.cc
@@ -8371,6 +8377,8 @@ FILE: ../../../flutter/impeller/renderer/command.cc
 FILE: ../../../flutter/impeller/renderer/command.h
 FILE: ../../../flutter/impeller/renderer/command_buffer.cc
 FILE: ../../../flutter/impeller/renderer/command_buffer.h
+FILE: ../../../flutter/impeller/renderer/command_queue.cc
+FILE: ../../../flutter/impeller/renderer/command_queue.h
 FILE: ../../../flutter/impeller/renderer/compute_pass.cc
 FILE: ../../../flutter/impeller/renderer/compute_pass.h
 FILE: ../../../flutter/impeller/renderer/compute_pipeline_builder.cc

impeller/aiks/aiks_context.cc

@@ -53,6 +53,7 @@ bool AiksContext::Render(const Picture& picture,
   }
 
   fml::ScopedCleanupClosure closure([&]() {
+    content_context_->FlushCommandBuffers();
     if (reset_host_buffer) {
       content_context_->GetTransientsBuffer().Reset();
     }

impeller/aiks/aiks_unittests.cc

@@ -141,8 +141,7 @@ TEST_P(AiksTest, CanRenderColorFilterWithInvertColorsDrawPaint) {
 namespace {
 bool GenerateMipmap(const std::shared_ptr<Context>& context,
                     std::shared_ptr<Texture> texture,
-                    std::string label,
-                    bool async_submit) {
+                    std::string label) {
   auto buffer = context->CreateCommandBuffer();
   if (!buffer) {
     return false;
@@ -152,23 +151,19 @@ bool GenerateMipmap(const std::shared_ptr<Context>& context,
     return false;
   }
   pass->GenerateMipmap(std::move(texture), std::move(label));
-  if (async_submit) {
-    return buffer->EncodeAndSubmit(pass, context->GetResourceAllocator());
-  }
 
   pass->EncodeCommands(context->GetResourceAllocator());
-  return buffer->SubmitCommands();
+  return context->GetCommandQueue()->Submit({buffer}).ok();
 }
 
 void CanRenderTiledTexture(AiksTest* aiks_test,
                            Entity::TileMode tile_mode,
-                           bool async_submit = false,
                            Matrix local_matrix = {}) {
   auto context = aiks_test->GetContext();
   ASSERT_TRUE(context);
   auto texture = aiks_test->CreateTextureForFixture("table_mountain_nx.png",
                                                     /*enable_mipmapping=*/true);
-  GenerateMipmap(context, texture, "table_mountain_nx", async_submit);
+  GenerateMipmap(context, texture, "table_mountain_nx");
   Canvas canvas;
   canvas.Scale(aiks_test->GetContentScale());
   canvas.Translate({100.0f, 100.0f, 0});
@@ -215,10 +210,6 @@ TEST_P(AiksTest, CanRenderTiledTextureClamp) {
   CanRenderTiledTexture(this, Entity::TileMode::kClamp);
 }
 
-TEST_P(AiksTest, CanRenderTiledTextureClampAsync) {
-  CanRenderTiledTexture(this, Entity::TileMode::kClamp, /*async_submit=*/true);
-}
-
 TEST_P(AiksTest, CanRenderTiledTextureRepeat) {
   CanRenderTiledTexture(this, Entity::TileMode::kRepeat);
 }
@@ -232,7 +223,7 @@ TEST_P(AiksTest, CanRenderTiledTextureDecal) {
 }
 
 TEST_P(AiksTest, CanRenderTiledTextureClampWithTranslate) {
-  CanRenderTiledTexture(this, Entity::TileMode::kClamp, /*async_submit=*/false,
+  CanRenderTiledTexture(this, Entity::TileMode::kClamp,
                         Matrix::MakeTranslation({172.f, 172.f, 0.f}));
 }
 

impeller/aiks/testing/context_mock.h

@@ -111,6 +111,11 @@ class ContextMock : public Context {
               (),
               (const, override));
 
+  MOCK_METHOD(std::shared_ptr<CommandQueue>,
+              GetCommandQueue,
+              (),
+              (const override));
+
   MOCK_METHOD(void, Shutdown, (), (override));
 };
 

impeller/aiks/testing/context_spy.cc

@@ -3,12 +3,23 @@
 // found in the LICENSE file.
 
 #include <memory>
+#include "impeller/renderer/command_buffer.h"
+#include "impeller/renderer/command_queue.h"
 
 #include "impeller/aiks/testing/context_spy.h"
 
 namespace impeller {
 namespace testing {
 
+fml::Status NoopCommandQueue::Submit(
+    const std::vector<std::shared_ptr<CommandBuffer>>& buffers,
+    const CompletionCallback& completion_callback) {
+  if (completion_callback) {
+    completion_callback(CommandBuffer::Status::kCompleted);
+  }
+  return fml::Status();
+}
+
 std::shared_ptr<ContextSpy> ContextSpy::Make() {
   return std::shared_ptr<ContextSpy>(new ContextSpy());
 }
@@ -50,6 +61,10 @@ std::shared_ptr<ContextMock> ContextSpy::MakeContext(
     return real_context->GetPipelineLibrary();
   });
 
+  ON_CALL(*mock_context, GetCommandQueue).WillByDefault([shared_this]() {
+    return shared_this->command_queue_;
+  });
+
   ON_CALL(*mock_context, CreateCommandBuffer)
       .WillByDefault([real_context, shared_this]() {
         auto real_buffer = real_context->CreateCommandBuffer();

impeller/aiks/testing/context_spy.h

@@ -9,10 +9,18 @@
 
 #include "impeller/aiks/testing/context_mock.h"
 #include "impeller/entity/contents/test/recording_render_pass.h"
+#include "impeller/renderer/command_queue.h"
 
 namespace impeller {
 namespace testing {
 
+class NoopCommandQueue : public CommandQueue {
+ public:
+  fml::Status Submit(
+      const std::vector<std::shared_ptr<CommandBuffer>>& buffers,
+      const CompletionCallback& completion_callback = {}) override;
+};
+
 /// Forwards calls to a real Context but can store information about how
 /// the Context was used.
 class ContextSpy : public std::enable_shared_from_this<ContextSpy> {
@@ -23,6 +31,8 @@ class ContextSpy : public std::enable_shared_from_this<ContextSpy> {
       const std::shared_ptr<Context>& real_context);
 
   std::vector<std::shared_ptr<RecordingRenderPass>> render_passes_;
+  std::shared_ptr<CommandQueue> command_queue_ =
+      std::make_shared<NoopCommandQueue>();
 
  private:
   ContextSpy() = default;

impeller/entity/contents/content_context.cc

@@ -200,7 +200,8 @@ ContentContext::ContentContext(
                                ? std::make_shared<RenderTargetCache>(
                                      context_->GetResourceAllocator())
                                : std::move(render_target_allocator)),
-      host_buffer_(HostBuffer::Create(context_->GetResourceAllocator())) {
+      host_buffer_(HostBuffer::Create(context_->GetResourceAllocator())),
+      pending_command_buffers_(std::make_unique<PendingCommandBuffers>()) {
   if (!context_ || !context_->IsValid()) {
     return;
   }
@@ -477,9 +478,10 @@ fml::StatusOr<RenderTarget> ContentContext::MakeSubpass(
     return fml::Status(fml::StatusCode::kUnknown, "");
   }
 
-  if (!sub_command_buffer->EncodeAndSubmit(sub_renderpass)) {
+  if (!sub_renderpass->EncodeCommands()) {
     return fml::Status(fml::StatusCode::kUnknown, "");
   }
+  RecordCommandBuffer(std::move(sub_command_buffer));
 
   return subpass_target;
 }
@@ -532,4 +534,15 @@ void ContentContext::ClearCachedRuntimeEffectPipeline(
   }
 }
 
+void ContentContext::RecordCommandBuffer(
+    std::shared_ptr<CommandBuffer> command_buffer) const {
+  pending_command_buffers_->command_buffers.push_back(
+      std::move(command_buffer));
+}
+
+void ContentContext::FlushCommandBuffers() const {
+  auto buffers = std::move(pending_command_buffers_->command_buffers);
+  GetContext()->GetCommandQueue()->Submit(buffers);
+}
+
 }  // namespace impeller

impeller/entity/contents/content_context.h

@@ -18,6 +18,7 @@
 #include "impeller/core/host_buffer.h"
 #include "impeller/entity/entity.h"
 #include "impeller/renderer/capabilities.h"
+#include "impeller/renderer/command_buffer.h"
 #include "impeller/renderer/pipeline.h"
 #include "impeller/renderer/pipeline_descriptor.h"
 #include "impeller/renderer/render_target.h"
@@ -268,6 +269,12 @@ using TiledTextureExternalPipeline =
                     TiledTextureFillExternalFragmentShader>;
 #endif  // IMPELLER_ENABLE_OPENGLES
 
+// A struct used to isolate command buffer storage from the content
+// context options to preserve const-ness.
+struct PendingCommandBuffers {
+  std::vector<std::shared_ptr<CommandBuffer>> command_buffers;
+};
+
 /// Pipeline state configuration.
 ///
 /// Each unique combination of these options requires a different pipeline state
@@ -715,6 +722,10 @@ class ContentContext {
 
   void SetWireframe(bool wireframe);
 
+  void RecordCommandBuffer(std::shared_ptr<CommandBuffer> command_buffer) const;
+
+  void FlushCommandBuffers() const;
+
   using SubpassCallback =
       std::function<bool(const ContentContext&, RenderPass&)>;
 
@@ -1005,6 +1016,7 @@ class ContentContext {
 #endif  // IMPELLER_ENABLE_3D
   std::shared_ptr<RenderTargetAllocator> render_target_cache_;
   std::shared_ptr<HostBuffer> host_buffer_;
+  std::unique_ptr<PendingCommandBuffers> pending_command_buffers_;
   bool wireframe_ = false;
 
   ContentContext(const ContentContext&) = delete;

impeller/entity/contents/content_context_unittests.cc

@@ -4,13 +4,15 @@
 
 #include <cstdint>
 
+#include "fml/logging.h"
 #include "gtest/gtest.h"
 
 #include "impeller/core/allocator.h"
 #include "impeller/core/device_buffer_descriptor.h"
 #include "impeller/entity/contents/content_context.h"
 #include "impeller/geometry/color.h"
 #include "impeller/renderer/capabilities.h"
+#include "impeller/renderer/command_queue.h"
 #include "impeller/renderer/pipeline.h"
 #include "impeller/renderer/pipeline_descriptor.h"
 
@@ -52,6 +54,7 @@ class FakeContext : public Context {
   std::shared_ptr<PipelineLibrary> GetPipelineLibrary() const {
     return nullptr;
   }
+  std::shared_ptr<CommandQueue> GetCommandQueue() const { FML_UNREACHABLE(); }
   std::shared_ptr<CommandBuffer> CreateCommandBuffer() const { return nullptr; }
   void Shutdown() {}
 

impeller/entity/entity_pass.cc

@@ -387,11 +387,12 @@ bool EntityPass::Render(ContentContext& renderer,
       blit_pass->AddCopy(
           offscreen_target.GetRenderTarget().GetRenderTargetTexture(),
           root_render_target.GetRenderTargetTexture());
-      if (!command_buffer->EncodeAndSubmit(
-              blit_pass, renderer.GetContext()->GetResourceAllocator())) {
+      if (!blit_pass->EncodeCommands(
+              renderer.GetContext()->GetResourceAllocator())) {
         VALIDATION_LOG << "Failed to encode root pass blit command.";
         return false;
       }
+      renderer.RecordCommandBuffer(std::move(command_buffer));
     } else {
       auto render_pass = command_buffer->CreateRenderPass(root_render_target);
       render_pass->SetLabel("EntityPass Root Render Pass");
@@ -415,10 +416,11 @@ bool EntityPass::Render(ContentContext& renderer,
         }
       }
 
-      if (!command_buffer->EncodeAndSubmit(render_pass)) {
+      if (!render_pass->EncodeCommands()) {
         VALIDATION_LOG << "Failed to encode root pass command buffer.";
         return false;
       }
+      renderer.RecordCommandBuffer(std::move(command_buffer));
     }
 
     return true;
@@ -855,8 +857,7 @@ bool EntityPass::OnRender(
         collapsed_parent_pass) const {
   TRACE_EVENT0("impeller", "EntityPass::OnRender");
 
-  const std::shared_ptr<Context>& context = renderer.GetContext();
-  InlinePassContext pass_context(context, pass_target,
+  InlinePassContext pass_context(renderer, pass_target,
                                  GetTotalPassReads(renderer), GetElementCount(),
                                  collapsed_parent_pass);
   if (!pass_context.IsValid()) {