Wire up render loop.

engine/src/flutter/impeller/impeller/BUILD.gn

@@ -30,8 +30,8 @@ source_set("impeller") {
     "compositor/renderer.mm",
     "compositor/shader_library.h",
     "compositor/shader_library.mm",
-    "compositor/surface.cc",
     "compositor/surface.h",
+    "compositor/surface.mm",
   ]
 
   geometry_sources = [

engine/src/flutter/impeller/impeller/compositor/context.h

@@ -18,11 +18,14 @@ class Context {
 
   bool IsValid() const;
 
+  id<MTLCommandQueue> GetRenderQueue() const;
+
+  id<MTLCommandQueue> GetTransferQueue() const;
+
  private:
   id<MTLDevice> device_;
   id<MTLCommandQueue> render_queue_;
   id<MTLCommandQueue> transfer_queue_;
-
   bool is_valid_ = false;
 
   FML_DISALLOW_COPY_AND_ASSIGN(Context);

engine/src/flutter/impeller/impeller/compositor/context.mm

@@ -32,4 +32,12 @@ bool Context::IsValid() const {
   return is_valid_;
 }
 
+id<MTLCommandQueue> Context::GetRenderQueue() const {
+  return render_queue_;
+}
+
+id<MTLCommandQueue> Context::GetTransferQueue() const {
+  return transfer_queue_;
+}
+
 }  // namespace impeller

engine/src/flutter/impeller/impeller/compositor/renderer.h

@@ -4,8 +4,11 @@
 
 #pragma once
 
-#include "context.h"
+#include <memory>
+
 #include "flutter/fml/macros.h"
+#include "impeller/compositor/context.h"
+#include "impeller/compositor/surface.h"
 #include "impeller/geometry/size.h"
 
 namespace impeller {
@@ -23,7 +26,8 @@ class Renderer {
   bool Render();
 
  private:
-  Context context_;
+  std::shared_ptr<Context> context_;
+  std::unique_ptr<Surface> surface_;
   Size size_;
   bool is_valid_ = false;
 

engine/src/flutter/impeller/impeller/compositor/renderer.mm

@@ -2,14 +2,20 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "renderer.h"
+#include "impeller/compositor/renderer.h"
 
 #include "flutter/fml/logging.h"
 
 namespace impeller {
 
-Renderer::Renderer() {
-  if (!context_.IsValid()) {
+Renderer::Renderer()
+    : context_(std::make_shared<Context>()),
+      surface_(std::make_unique<Surface>(context_)) {
+  if (!context_->IsValid()) {
+    return;
+  }
+
+  if (!surface_->IsValid()) {
     return;
   }
 
@@ -40,7 +46,7 @@ bool Renderer::Render() {
     return false;
   }
 
-  return true;
+  return surface_->Render();
 }
 
 }  // namespace impeller

engine/src/flutter/impeller/impeller/compositor/surface.h

@@ -4,17 +4,30 @@
 
 #pragma once
 
+#include <dispatch/dispatch.h>
+
+#include <memory>
+
 #include "flutter/fml/macros.h"
+#include "impeller/compositor/context.h"
 
 namespace impeller {
 
 class Surface {
  public:
-  Surface();
+  Surface(std::shared_ptr<Context> context);
 
   ~Surface();
 
+  bool IsValid() const;
+
+  bool Render() const;
+
  private:
+  std::shared_ptr<Context> context_;
+  dispatch_semaphore_t frames_in_flight_sema_;
+  bool is_valid_ = false;
+
   FML_DISALLOW_COPY_AND_ASSIGN(Surface);
 };
 

engine/src/flutter/impeller/impeller/compositor/surface.mm

@@ -0,0 +1,52 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "impeller/compositor/surface.h"
+
+#include "flutter/fml/logging.h"
+
+namespace impeller {
+
+constexpr size_t kMaxFramesInFlight = 3u;
+
+Surface::Surface(std::shared_ptr<Context> context)
+    : context_(std::move(context)),
+      frames_in_flight_sema_(::dispatch_semaphore_create(kMaxFramesInFlight)) {
+  if (!context_ || !context_->IsValid()) {
+    return;
+  }
+
+  is_valid_ = true;
+}
+
+Surface::~Surface() = default;
+
+bool Surface::IsValid() const {
+  return is_valid_;
+}
+
+bool Surface::Render() const {
+  if (!IsValid()) {
+    return false;
+  }
+
+  auto command_buffer = [context_->GetRenderQueue() commandBuffer];
+
+  if (!command_buffer) {
+    return false;
+  }
+
+  ::dispatch_semaphore_wait(frames_in_flight_sema_, DISPATCH_TIME_FOREVER);
+
+  __block dispatch_semaphore_t block_sema = frames_in_flight_sema_;
+  [command_buffer addCompletedHandler:^(id<MTLCommandBuffer> buffer) {
+    ::dispatch_semaphore_signal(block_sema);
+  }];
+
+  [command_buffer commit];
+
+  return true;
+}
+
+}  // namespace impeller