From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Andy Dill <andy.dill@gmail.com>
Date: Thu, 30 Jan 2020 09:36:07 -0800
Subject: feat: enable off-screen rendering with viz compositor

This patch adds hooks in the relevant places that allow for off-screen
rendering with the viz compositor by way of a custom HostDisplayClient
and LayeredWindowUpdater.

diff --git a/components/viz/host/host_display_client.cc b/components/viz/host/host_display_client.cc
index 3b00759e513dc7e19fd68398e853c8ce6ac73905..47f4e7cc2e8b3141dcaf9e7a498fec32c9342f40 100644
--- a/components/viz/host/host_display_client.cc
+++ b/components/viz/host/host_display_client.cc
@@ -45,9 +45,9 @@ void HostDisplayClient::OnDisplayReceivedCALayerParams(
 }
 #endif
 
-#if defined(OS_WIN)
 void HostDisplayClient::CreateLayeredWindowUpdater(
     mojo::PendingReceiver<mojom::LayeredWindowUpdater> receiver) {
+#if defined(OS_WIN)
   if (!NeedsToUseLayerWindow(widget_)) {
     DLOG(ERROR) << "HWND shouldn't be using a layered window";
     return;
@@ -55,8 +55,12 @@ void HostDisplayClient::CreateLayeredWindowUpdater(
 
   layered_window_updater_ =
       std::make_unique<LayeredWindowUpdaterImpl>(widget_, std::move(receiver));
-}
+#else
+  CHECK(false) << "Chromium is calling CreateLayeredWindowUpdater for non-OSR "
+                  "windows on POSIX platforms, something is wrong with "
+                  "Electron's OSR implementation.";
 #endif
+}
 
 // TODO(crbug.com/1052397): Revisit the macro expression once build flag switch
 // of lacros-chrome is complete.
diff --git a/components/viz/host/host_display_client.h b/components/viz/host/host_display_client.h
index 5e260e13762f61971c99f755e93d73aa794d9175..a57770718b71def04fa35c7655d9368a58f39f20 100644
--- a/components/viz/host/host_display_client.h
+++ b/components/viz/host/host_display_client.h
@@ -39,10 +39,9 @@ class VIZ_HOST_EXPORT HostDisplayClient : public mojom::DisplayClient {
       const gfx::CALayerParams& ca_layer_params) override;
 #endif
 
-#if defined(OS_WIN)
+ protected:
   void CreateLayeredWindowUpdater(
       mojo::PendingReceiver<mojom::LayeredWindowUpdater> receiver) override;
-#endif
 
 // TODO(crbug.com/1052397): Revisit the macro expression once build flag switch
 // of lacros-chrome is complete.
diff --git a/components/viz/host/layered_window_updater_impl.cc b/components/viz/host/layered_window_updater_impl.cc
index b04f654fe820f821b18e059cdd40085fc2384c4e..ee22012b01ef92bb3b32b5b1081609a7bdfb0d93 100644
--- a/components/viz/host/layered_window_updater_impl.cc
+++ b/components/viz/host/layered_window_updater_impl.cc
@@ -44,7 +44,9 @@ void LayeredWindowUpdaterImpl::OnAllocatedSharedMemory(
   // |region|'s handle will close when it goes out of scope.
 }
 
-void LayeredWindowUpdaterImpl::Draw(DrawCallback draw_callback) {
+void LayeredWindowUpdaterImpl::Draw(
+    const gfx::Rect& damage_rect,
+    DrawCallback draw_callback) {
   TRACE_EVENT0("viz", "LayeredWindowUpdaterImpl::Draw");
 
   if (!canvas_) {
diff --git a/components/viz/host/layered_window_updater_impl.h b/components/viz/host/layered_window_updater_impl.h
index 1026b739d283f0fc252fa2af83a6d4cf51bc8553..fe562ab60ce98b8bb0c5080a6428deb319a4dd04 100644
--- a/components/viz/host/layered_window_updater_impl.h
+++ b/components/viz/host/layered_window_updater_impl.h
@@ -35,7 +35,7 @@ class VIZ_HOST_EXPORT LayeredWindowUpdaterImpl
   // mojom::LayeredWindowUpdater implementation.
   void OnAllocatedSharedMemory(const gfx::Size& pixel_size,
                                base::UnsafeSharedMemoryRegion region) override;
-  void Draw(DrawCallback draw_callback) override;
+  void Draw(const gfx::Rect& damage_rect, DrawCallback draw_callback) override;
 
  private:
   const HWND hwnd_;
diff --git a/components/viz/service/BUILD.gn b/components/viz/service/BUILD.gn
index 0f6a5a2fa3d82ae76889ef55af14e18b86cacffc..e33cd6305f53aa9287c61bf2d38848f878a14d30 100644
--- a/components/viz/service/BUILD.gn
+++ b/components/viz/service/BUILD.gn
@@ -119,6 +119,8 @@ viz_component("service") {
     "display_embedder/output_surface_provider_impl.h",
     "display_embedder/server_shared_bitmap_manager.cc",
     "display_embedder/server_shared_bitmap_manager.h",
+    "display_embedder/software_output_device_proxy.cc",
+    "display_embedder/software_output_device_proxy.h",
     "display_embedder/software_output_surface.cc",
     "display_embedder/software_output_surface.h",
     "display_embedder/viz_process_context_provider.cc",
diff --git a/components/viz/service/display_embedder/output_surface_provider.h b/components/viz/service/display_embedder/output_surface_provider.h
index 77d463e683d8b8d3a202681a6884eacaab79d70d..05d51cb2637d34c073cd0025e365803633459a86 100644
--- a/components/viz/service/display_embedder/output_surface_provider.h
+++ b/components/viz/service/display_embedder/output_surface_provider.h
@@ -39,7 +39,8 @@ class OutputSurfaceProvider {
       mojom::DisplayClient* display_client,
       DisplayCompositorMemoryAndTaskController* gpu_dependency,
       const RendererSettings& renderer_settings,
-      const DebugRendererSettings* debug_settings) = 0;
+      const DebugRendererSettings* debug_settings,
+      bool offscreen) = 0;
 };
 
 }  // namespace viz
diff --git a/components/viz/service/display_embedder/output_surface_provider_impl.cc b/components/viz/service/display_embedder/output_surface_provider_impl.cc
index 79c800e77a160cc0b10a29dd560d37e19c9d05fd..a9b1b267c97ed513890ba8466f66c3eafcbd5d5b 100644
--- a/components/viz/service/display_embedder/output_surface_provider_impl.cc
+++ b/components/viz/service/display_embedder/output_surface_provider_impl.cc
@@ -25,6 +25,7 @@
 #include "components/viz/service/display_embedder/server_shared_bitmap_manager.h"
 #include "components/viz/service/display_embedder/skia_output_surface_dependency_impl.h"
 #include "components/viz/service/display_embedder/skia_output_surface_impl.h"
+#include "components/viz/service/display_embedder/software_output_device_proxy.h"
 #include "components/viz/service/display_embedder/software_output_surface.h"
 #include "components/viz/service/display_embedder/viz_process_context_provider.h"
 #include "components/viz/service/gl/gpu_service_impl.h"
@@ -38,6 +39,7 @@
 #include "gpu/ipc/scheduler_sequence.h"
 #include "gpu/ipc/service/gpu_channel_manager_delegate.h"
 #include "gpu/ipc/service/image_transport_surface.h"
+#include "services/viz/privileged/mojom/compositing/layered_window_updater.mojom.h"
 #include "ui/base/ui_base_switches.h"
 #include "ui/gl/gl_context.h"
 #include "ui/gl/init/gl_factory.h"
@@ -130,7 +132,8 @@ std::unique_ptr<OutputSurface> OutputSurfaceProviderImpl::CreateOutputSurface(
     mojom::DisplayClient* display_client,
     DisplayCompositorMemoryAndTaskController* gpu_dependency,
     const RendererSettings& renderer_settings,
-    const DebugRendererSettings* debug_settings) {
+    const DebugRendererSettings* debug_settings,
+    bool offscreen) {
 #if BUILDFLAG(IS_CHROMEOS_ASH)
   if (surface_handle == gpu::kNullSurfaceHandle)
     return std::make_unique<OutputSurfaceUnified>();
@@ -142,7 +145,7 @@ std::unique_ptr<OutputSurface> OutputSurfaceProviderImpl::CreateOutputSurface(
 
   if (!gpu_compositing) {
     output_surface = std::make_unique<SoftwareOutputSurface>(
-        CreateSoftwareOutputDeviceForPlatform(surface_handle, display_client));
+        CreateSoftwareOutputDeviceForPlatform(surface_handle, display_client, offscreen));
   } else if (renderer_settings.use_skia_renderer) {
     DCHECK(gpu_dependency);
     {
@@ -241,10 +244,22 @@ std::unique_ptr<OutputSurface> OutputSurfaceProviderImpl::CreateOutputSurface(
 std::unique_ptr<SoftwareOutputDevice>
 OutputSurfaceProviderImpl::CreateSoftwareOutputDeviceForPlatform(
     gpu::SurfaceHandle surface_handle,
-    mojom::DisplayClient* display_client) {
+    mojom::DisplayClient* display_client,
+    bool offscreen) {
   if (headless_)
     return std::make_unique<SoftwareOutputDevice>();
 
+#if !defined(OS_MAC)
+  if (offscreen) {
+    DCHECK(display_client);
+    mojom::LayeredWindowUpdaterPtr layered_window_updater;
+    display_client->CreateLayeredWindowUpdater(
+        mojo::MakeRequest(&layered_window_updater));
+    return std::make_unique<SoftwareOutputDeviceProxy>(
+        std::move(layered_window_updater));
+  }
+#endif
+
 #if defined(OS_WIN)
   return CreateSoftwareOutputDeviceWin(surface_handle, &output_device_backing_,
                                        display_client);
diff --git a/components/viz/service/display_embedder/output_surface_provider_impl.h b/components/viz/service/display_embedder/output_surface_provider_impl.h
index a6bb42cdbc567f526cc70c5c4d9b967274dc0332..d116844635922c8a1086dfa13063b8ae8b43ce59 100644
--- a/components/viz/service/display_embedder/output_surface_provider_impl.h
+++ b/components/viz/service/display_embedder/output_surface_provider_impl.h
@@ -61,12 +61,14 @@ class VIZ_SERVICE_EXPORT OutputSurfaceProviderImpl
       mojom::DisplayClient* display_client,
       DisplayCompositorMemoryAndTaskController* gpu_dependency,
       const RendererSettings& renderer_settings,
-      const DebugRendererSettings* debug_settings) override;
+      const DebugRendererSettings* debug_settings,
+      bool offscreen) override;
 
  private:
   std::unique_ptr<SoftwareOutputDevice> CreateSoftwareOutputDeviceForPlatform(
       gpu::SurfaceHandle surface_handle,
-      mojom::DisplayClient* display_client);
+      mojom::DisplayClient* display_client,
+      bool offscreen);
 
   GpuServiceImpl* const gpu_service_impl_;
   gpu::CommandBufferTaskExecutor* const task_executor_;
diff --git a/components/viz/service/display_embedder/software_output_device_mac.cc b/components/viz/service/display_embedder/software_output_device_mac.cc
index 49149081cc603f14eacee647cbb2fcf8ed5e66fd..9ff3f2ee203403fdaa31edb8a0bcc000c4d214d7 100644
--- a/components/viz/service/display_embedder/software_output_device_mac.cc
+++ b/components/viz/service/display_embedder/software_output_device_mac.cc
@@ -102,6 +102,8 @@ void SoftwareOutputDeviceMac::UpdateAndCopyBufferDamage(
 
 SkCanvas* SoftwareOutputDeviceMac::BeginPaint(
     const gfx::Rect& new_damage_rect) {
+  last_damage = new_damage_rect;
+
   // Record the previous paint buffer.
   Buffer* previous_paint_buffer =
       buffer_queue_.empty() ? nullptr : buffer_queue_.back().get();
@@ -187,6 +189,7 @@ void SoftwareOutputDeviceMac::EndPaint() {
     ca_layer_params.is_empty = false;
     ca_layer_params.scale_factor = scale_factor_;
     ca_layer_params.pixel_size = pixel_size_;
+    ca_layer_params.damage = last_damage;
     ca_layer_params.io_surface_mach_port.reset(
         IOSurfaceCreateMachPort(current_paint_buffer_->io_surface));
     client_->SoftwareDeviceUpdatedCALayerParams(ca_layer_params);
diff --git a/components/viz/service/display_embedder/software_output_device_mac.h b/components/viz/service/display_embedder/software_output_device_mac.h
index f3867356e3d641416e00e6d115ae9ae2a0be90ab..b1d192d2b20ccb63fba07093101d745e5ffe86dd 100644
--- a/components/viz/service/display_embedder/software_output_device_mac.h
+++ b/components/viz/service/display_embedder/software_output_device_mac.h
@@ -56,6 +56,7 @@ class VIZ_SERVICE_EXPORT SoftwareOutputDeviceMac : public SoftwareOutputDevice {
   void UpdateAndCopyBufferDamage(Buffer* previous_paint_buffer,
                                  const SkRegion& new_damage_rect);
 
+  gfx::Rect last_damage;
   gfx::Size pixel_size_;
   float scale_factor_ = 1;
 
diff --git a/components/viz/service/display_embedder/software_output_device_proxy.cc b/components/viz/service/display_embedder/software_output_device_proxy.cc
new file mode 100644
index 0000000000000000000000000000000000000000..4efea02f80f8b6818291321a7c63f0f4815a5b98
--- /dev/null
+++ b/components/viz/service/display_embedder/software_output_device_proxy.cc
@@ -0,0 +1,157 @@
+// Copyright 2014 The Chromium 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 "components/viz/service/display_embedder/software_output_device_proxy.h"
+
+#include "base/memory/unsafe_shared_memory_region.h"
+#include "base/threading/thread_checker.h"
+#include "base/trace_event/trace_event.h"
+#include "components/viz/common/resources/resource_sizes.h"
+#include "components/viz/service/display_embedder/output_device_backing.h"
+#include "mojo/public/cpp/system/platform_handle.h"
+#include "services/viz/privileged/mojom/compositing/layered_window_updater.mojom.h"
+#include "skia/ext/platform_canvas.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+#include "ui/gfx/skia_util.h"
+
+#if defined(OS_WIN)
+#include "skia/ext/skia_utils_win.h"
+#include "ui/gfx/gdi_util.h"
+#include "ui/gfx/win/hwnd_util.h"
+#else
+#include "mojo/public/cpp/base/shared_memory_utils.h"
+#endif
+
+namespace viz {
+
+SoftwareOutputDeviceBase::~SoftwareOutputDeviceBase() {
+  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
+  DCHECK(!in_paint_);
+}
+
+void SoftwareOutputDeviceBase::Resize(const gfx::Size& viewport_pixel_size,
+                                         float scale_factor) {
+  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
+  DCHECK(!in_paint_);
+
+  if (viewport_pixel_size_ == viewport_pixel_size)
+    return;
+
+  viewport_pixel_size_ = viewport_pixel_size;
+  ResizeDelegated();
+}
+
+SkCanvas* SoftwareOutputDeviceBase::BeginPaint(
+    const gfx::Rect& damage_rect) {
+  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
+  DCHECK(!in_paint_);
+
+  damage_rect_ = damage_rect;
+  in_paint_ = true;
+  return BeginPaintDelegated();
+}
+
+void SoftwareOutputDeviceBase::EndPaint() {
+  DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
+  DCHECK(in_paint_);
+
+  in_paint_ = false;
+
+  gfx::Rect intersected_damage_rect = damage_rect_;
+  intersected_damage_rect.Intersect(gfx::Rect(viewport_pixel_size_));
+  if (intersected_damage_rect.IsEmpty())
+    return;
+
+  EndPaintDelegated(intersected_damage_rect);
+}
+
+SoftwareOutputDeviceProxy::~SoftwareOutputDeviceProxy() = default;
+
+SoftwareOutputDeviceProxy::SoftwareOutputDeviceProxy(
+    mojom::LayeredWindowUpdaterPtr layered_window_updater)
+    : layered_window_updater_(std::move(layered_window_updater)) {
+  DCHECK(layered_window_updater_.is_bound());
+}
+
+void SoftwareOutputDeviceProxy::OnSwapBuffers(
+    SoftwareOutputDevice::SwapBuffersCallback swap_ack_callback) {
+  DCHECK(swap_ack_callback_.is_null());
+
+  // We aren't waiting on DrawAck() and can immediately run the callback.
+  if (!waiting_on_draw_ack_) {
+    task_runner_->PostTask(FROM_HERE,
+        base::BindOnce(std::move(swap_ack_callback), viewport_pixel_size_));
+    return;
+  }
+
+  swap_ack_callback_ = std::move(swap_ack_callback);
+}
+
+void SoftwareOutputDeviceProxy::ResizeDelegated() {
+  canvas_.reset();
+
+  size_t required_bytes;
+  if (!ResourceSizes::MaybeSizeInBytes(
+          viewport_pixel_size_, ResourceFormat::RGBA_8888, &required_bytes)) {
+    DLOG(ERROR) << "Invalid viewport size " << viewport_pixel_size_.ToString();
+    return;
+  }
+
+  base::UnsafeSharedMemoryRegion region =
+      base::UnsafeSharedMemoryRegion::Create(required_bytes);
+  if (!region.IsValid()) {
+    DLOG(ERROR) << "Failed to allocate " << required_bytes << " bytes";
+    return;
+  }
+
+  #if defined(WIN32)
+  canvas_ = skia::CreatePlatformCanvasWithSharedSection(
+      viewport_pixel_size_.width(), viewport_pixel_size_.height(), false,
+      region.GetPlatformHandle(), skia::CRASH_ON_FAILURE);
+  #else
+  shm_mapping_ = region.Map();
+  if (!shm_mapping_.IsValid()) {
+    DLOG(ERROR) << "Failed to map " << required_bytes << " bytes";
+    return;
+  }
+
+  canvas_ = skia::CreatePlatformCanvasWithPixels(
+      viewport_pixel_size_.width(), viewport_pixel_size_.height(), false,
+      static_cast<uint8_t*>(shm_mapping_.memory()), skia::CRASH_ON_FAILURE);
+  #endif
+
+  // Transfer region ownership to the browser process.
+  layered_window_updater_->OnAllocatedSharedMemory(viewport_pixel_size_,
+                                                   std::move(region));
+}
+
+SkCanvas* SoftwareOutputDeviceProxy::BeginPaintDelegated() {
+  return canvas_.get();
+}
+
+void SoftwareOutputDeviceProxy::EndPaintDelegated(
+    const gfx::Rect& damage_rect) {
+  DCHECK(!waiting_on_draw_ack_);
+
+  if (!canvas_)
+    return;
+
+  layered_window_updater_->Draw(damage_rect, base::BindOnce(
+      &SoftwareOutputDeviceProxy::DrawAck, base::Unretained(this)));
+  waiting_on_draw_ack_ = true;
+
+  TRACE_EVENT_ASYNC_BEGIN0("viz", "SoftwareOutputDeviceProxy::Draw", this);
+}
+
+void SoftwareOutputDeviceProxy::DrawAck() {
+  DCHECK(waiting_on_draw_ack_);
+  DCHECK(!swap_ack_callback_.is_null());
+
+  TRACE_EVENT_ASYNC_END0("viz", "SoftwareOutputDeviceProxy::Draw", this);
+
+  waiting_on_draw_ack_ = false;
+  std::move(swap_ack_callback_).Run(viewport_pixel_size_);
+}
+
+}  // namespace viz
diff --git a/components/viz/service/display_embedder/software_output_device_proxy.h b/components/viz/service/display_embedder/software_output_device_proxy.h
new file mode 100644
index 0000000000000000000000000000000000000000..48fa86caaab3c15764f105eb7ad2aecf2b89bf36
--- /dev/null
+++ b/components/viz/service/display_embedder/software_output_device_proxy.h
@@ -0,0 +1,90 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_VIZ_SERVICE_DISPLAY_EMBEDDER_SOFTWARE_OUTPUT_DEVICE_PROXY_H_
+#define COMPONENTS_VIZ_SERVICE_DISPLAY_EMBEDDER_SOFTWARE_OUTPUT_DEVICE_PROXY_H_
+
+#if defined(OS_WIN)
+#include <windows.h>
+#endif
+
+#include <memory>
+
+#include "base/memory/shared_memory_mapping.h"
+#include "base/threading/thread_checker.h"
+#include "components/viz/host/host_display_client.h"
+#include "components/viz/service/display/software_output_device.h"
+#include "components/viz/service/viz_service_export.h"
+#include "services/viz/privileged/mojom/compositing/display_private.mojom.h"
+#include "services/viz/privileged/mojom/compositing/layered_window_updater.mojom.h"
+
+namespace viz {
+
+// Shared base class for SoftwareOutputDevice implementations.
+class SoftwareOutputDeviceBase : public SoftwareOutputDevice {
+ public:
+  SoftwareOutputDeviceBase() = default;
+  ~SoftwareOutputDeviceBase() override;
+
+  // SoftwareOutputDevice implementation.
+  void Resize(const gfx::Size& viewport_pixel_size,
+              float scale_factor) override;
+  SkCanvas* BeginPaint(const gfx::Rect& damage_rect) override;
+  void EndPaint() override;
+
+  // Called from Resize() if |viewport_pixel_size_| has changed.
+  virtual void ResizeDelegated() = 0;
+
+  // Called from BeginPaint() and should return an SkCanvas.
+  virtual SkCanvas* BeginPaintDelegated() = 0;
+
+  // Called from EndPaint() if there is damage.
+  virtual void EndPaintDelegated(const gfx::Rect& damage_rect) = 0;
+
+ private:
+  bool in_paint_ = false;
+
+  THREAD_CHECKER(thread_checker_);
+
+  DISALLOW_COPY_AND_ASSIGN(SoftwareOutputDeviceBase);
+};
+
+// SoftwareOutputDevice implementation that draws indirectly. An implementation
+// of mojom::LayeredWindowUpdater in the browser process handles the actual
+// drawing. Pixel backing is in SharedMemory so no copying between processes
+// is required.
+class SoftwareOutputDeviceProxy : public SoftwareOutputDeviceBase {
+ public:
+  explicit SoftwareOutputDeviceProxy(
+      mojom::LayeredWindowUpdaterPtr layered_window_updater);
+  ~SoftwareOutputDeviceProxy() override;
+
+  // SoftwareOutputDevice implementation.
+  void OnSwapBuffers(SoftwareOutputDevice::SwapBuffersCallback swap_ack_callback) override;
+
+  // SoftwareOutputDeviceBase implementation.
+  void ResizeDelegated() override;
+  SkCanvas* BeginPaintDelegated() override;
+  void EndPaintDelegated(const gfx::Rect& rect) override;
+
+ private:
+  // Runs |swap_ack_callback_| after draw has happened.
+  void DrawAck();
+
+  mojom::LayeredWindowUpdaterPtr layered_window_updater_;
+
+  std::unique_ptr<SkCanvas> canvas_;
+  bool waiting_on_draw_ack_ = false;
+  SoftwareOutputDevice::SwapBuffersCallback swap_ack_callback_;
+
+#if !defined(WIN32)
+  base::WritableSharedMemoryMapping shm_mapping_;
+#endif
+
+  DISALLOW_COPY_AND_ASSIGN(SoftwareOutputDeviceProxy);
+};
+
+}  // namespace viz
+
+#endif  // COMPONENTS_VIZ_SERVICE_DISPLAY_EMBEDDER_SOFTWARE_OUTPUT_DEVICE_PROXY_H_
diff --git a/components/viz/service/display_embedder/software_output_device_win.cc b/components/viz/service/display_embedder/software_output_device_win.cc
index 2bb30e5318b6b48c2e6d4b1f64a6a36c68f963d1..9e805f27a9d7d1c0aa68cdf9f48895c055ca7791 100644
--- a/components/viz/service/display_embedder/software_output_device_win.cc
+++ b/components/viz/service/display_embedder/software_output_device_win.cc
@@ -188,7 +188,7 @@ void SoftwareOutputDeviceWinProxy::EndPaintDelegated(
   if (!canvas_)
     return;
 
-  layered_window_updater_->Draw(base::BindOnce(
+  layered_window_updater_->Draw(damage_rect, base::BindOnce(
       &SoftwareOutputDeviceWinProxy::DrawAck, base::Unretained(this)));
   waiting_on_draw_ack_ = true;
 
diff --git a/components/viz/service/frame_sinks/root_compositor_frame_sink_impl.cc b/components/viz/service/frame_sinks/root_compositor_frame_sink_impl.cc
index 8112abf9ca0bf214721f5996bb59f7458d9347d2..8b3c2a4cce0c4789fadd555b360dea2c145ae1a4 100644
--- a/components/viz/service/frame_sinks/root_compositor_frame_sink_impl.cc
+++ b/components/viz/service/frame_sinks/root_compositor_frame_sink_impl.cc
@@ -46,7 +46,8 @@ RootCompositorFrameSinkImpl::Create(
       params->gpu_compositing, params->widget, params->renderer_settings);
   auto output_surface = output_surface_provider->CreateOutputSurface(
       params->widget, params->gpu_compositing, display_client.get(),
-      display_controller.get(), params->renderer_settings, debug_settings);
+      display_controller.get(), params->renderer_settings, debug_settings,
+      params->offscreen);
 
   // Creating output surface failed. The host can send a new request, possibly
   // with a different compositing mode.
diff --git a/content/browser/compositor/viz_process_transport_factory.cc b/content/browser/compositor/viz_process_transport_factory.cc
index 11ac1649ed0f5be1d12e8a30b8d170f86b8e9bb8..05746d9a561c3933ae0c5578467f20b486453943 100644
--- a/content/browser/compositor/viz_process_transport_factory.cc
+++ b/content/browser/compositor/viz_process_transport_factory.cc
@@ -414,8 +414,14 @@ void VizProcessTransportFactory::OnEstablishedGpuChannel(
   compositor_data.display_private.reset();
   root_params->display_private =
       compositor_data.display_private.BindNewEndpointAndPassReceiver();
-  compositor_data.display_client =
-      std::make_unique<HostDisplayClient>(compositor);
+  if (compositor->delegate()) {
+    compositor_data.display_client = compositor->delegate()->CreateHostDisplayClient(
+        compositor);
+    root_params->offscreen = compositor->delegate()->IsOffscreen();
+  } else {
+    compositor_data.display_client =
+        std::make_unique<HostDisplayClient>(compositor);
+  }
   root_params->display_client =
       compositor_data.display_client->GetBoundRemote(resize_task_runner_);
 
diff --git a/services/viz/privileged/mojom/compositing/display_private.mojom b/services/viz/privileged/mojom/compositing/display_private.mojom
index 0c9686f3c8070000bf5b180d9c06a8817d430c4a..4538b95f6e71708144eb7752438b1b31d60cb2ca 100644
--- a/services/viz/privileged/mojom/compositing/display_private.mojom
+++ b/services/viz/privileged/mojom/compositing/display_private.mojom
@@ -85,7 +85,6 @@ interface DisplayClient {
 
   // Creates a LayeredWindowUpdater implementation to draw into a layered
   // window.
-  [EnableIf=is_win]
   CreateLayeredWindowUpdater(pending_receiver<LayeredWindowUpdater> receiver);
 
   // Notifies that a swap has occurred and provides information about the pixel
diff --git a/services/viz/privileged/mojom/compositing/frame_sink_manager.mojom b/services/viz/privileged/mojom/compositing/frame_sink_manager.mojom
index a0b87925e0c9d02f586cc4e9446cbfcf12b7aa1c..71659834eec5237016f95f93defa9dcb30f0af52 100644
--- a/services/viz/privileged/mojom/compositing/frame_sink_manager.mojom
+++ b/services/viz/privileged/mojom/compositing/frame_sink_manager.mojom
@@ -30,6 +30,7 @@ struct RootCompositorFrameSinkParams {
   // Disables begin frame rate limiting for the display compositor.
   bool disable_frame_rate_limit = false;
   bool use_preferred_interval_for_video = false;
+  bool offscreen = false;
 
   [EnableIf=is_android]
   float refresh_rate;
diff --git a/services/viz/privileged/mojom/compositing/layered_window_updater.mojom b/services/viz/privileged/mojom/compositing/layered_window_updater.mojom
index 6b7fbb6cf13dc8ee6ade0878a9a2c1efc5d4d3f1..e2af75168cb914a7b3b4a6c9b6a285498c3f8e72 100644
--- a/services/viz/privileged/mojom/compositing/layered_window_updater.mojom
+++ b/services/viz/privileged/mojom/compositing/layered_window_updater.mojom
@@ -26,5 +26,5 @@ interface LayeredWindowUpdater {
   // Draws to the HWND by copying pixels from shared memory. Callback must be
   // called after draw operation is complete to signal shared memory can be
   // modified.
-  Draw() => ();
+  Draw(gfx.mojom.Rect damage_rect) => ();
 };
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index e1db8f745c077b2f57b39a48aeab434fe0e98541..ddafd1f2aa38ef30776fa89ffcf5d108be963ac9 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -77,6 +77,7 @@ class ExternalBeginFrameController;
 class DelegatedInkPointRenderer;
 }  // namespace mojom
 class ContextProvider;
+class HostDisplayClient;
 class HostFrameSinkManager;
 class LocalSurfaceId;
 class RasterContextProvider;
@@ -133,6 +134,16 @@ class COMPOSITOR_EXPORT ContextFactory {
   virtual viz::HostFrameSinkManager* GetHostFrameSinkManager() = 0;
 };
 
+class COMPOSITOR_EXPORT CompositorDelegate {
+ public:
+  virtual bool IsOffscreen() const = 0;
+  virtual std::unique_ptr<viz::HostDisplayClient> CreateHostDisplayClient(
+      ui::Compositor* compositor) = 0;
+
+ protected:
+  virtual ~CompositorDelegate() {}
+};
+
 // Compositor object to take care of GPU painting.
 // A Browser compositor object is responsible for generating the final
 // displayable form of pixels comprising a single widget's contents. It draws an
@@ -167,6 +178,9 @@ class COMPOSITOR_EXPORT Compositor : public cc::LayerTreeHostClient,
   // Schedules a redraw of the layer tree associated with this compositor.
   void ScheduleDraw();
 
+  CompositorDelegate* delegate() const { return delegate_; }
+  void SetDelegate(CompositorDelegate* delegate) { delegate_ = delegate; }
+
   // Sets the root of the layer tree drawn by this Compositor. The root layer
   // must have no parent. The compositor's root layer is reset if the root layer
   // is destroyed. NULL can be passed to reset the root layer, in which case the
@@ -435,6 +449,8 @@ class COMPOSITOR_EXPORT Compositor : public cc::LayerTreeHostClient,
 
   std::unique_ptr<PendingBeginFrameArgs> pending_begin_frame_args_;
 
+  CompositorDelegate* delegate_ = nullptr;
+
   // The root of the Layer tree drawn by this compositor.
   Layer* root_layer_ = nullptr;
 
diff --git a/ui/gfx/ca_layer_params.h b/ui/gfx/ca_layer_params.h
index 64af450ed36a982124c6fcce7056b4058140747a..dcee2ec9de0e759b868b0de2c7106b2cf084c41c 100644
--- a/ui/gfx/ca_layer_params.h
+++ b/ui/gfx/ca_layer_params.h
@@ -6,6 +6,7 @@
 #define UI_GFX_CA_LAYER_PARAMS_H_
 
 #include "build/build_config.h"
+#include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/gfx_export.h"
 
@@ -41,6 +42,8 @@ struct GFX_EXPORT CALayerParams {
   gfx::ScopedRefCountedIOSurfaceMachPort io_surface_mach_port;
 #endif
 
+  gfx::Rect damage;
+
   // The geometry of the frame.
   gfx::Size pixel_size;
   float scale_factor = 1.f;
diff --git a/ui/gfx/mojom/ca_layer_params.mojom b/ui/gfx/mojom/ca_layer_params.mojom
index de00e766ba17532e10dcf5d0fd31fa344920a9f7..7aaedf83ad22dcc1d2dd39a31cf7e08b7b6ba4d3 100644
--- a/ui/gfx/mojom/ca_layer_params.mojom
+++ b/ui/gfx/mojom/ca_layer_params.mojom
@@ -18,5 +18,6 @@ struct CALayerParams {
   bool is_empty;
   CALayerContent content;
   gfx.mojom.Size pixel_size;
+  gfx.mojom.Rect damage;
   float scale_factor;
 };
diff --git a/ui/gfx/mojom/ca_layer_params_mojom_traits.cc b/ui/gfx/mojom/ca_layer_params_mojom_traits.cc
index c1f21d7f4348df96f7be5c0adb1b9650304048e0..760c849aebba70e575e59883655d707f36c5424a 100644
--- a/ui/gfx/mojom/ca_layer_params_mojom_traits.cc
+++ b/ui/gfx/mojom/ca_layer_params_mojom_traits.cc
@@ -52,6 +52,9 @@ bool StructTraits<gfx::mojom::CALayerParamsDataView, gfx::CALayerParams>::Read(
   if (!data.ReadPixelSize(&out->pixel_size))
     return false;
 
+  if (!data.ReadDamage(&out->damage))
+    return false;
+
   out->scale_factor = data.scale_factor();
   return true;
 }
diff --git a/ui/gfx/mojom/ca_layer_params_mojom_traits.h b/ui/gfx/mojom/ca_layer_params_mojom_traits.h
index 4cac766eae3161baedac4202f694129cd90c80de..0821495ad22944d8856bb750cac8912a2f8328c3 100644
--- a/ui/gfx/mojom/ca_layer_params_mojom_traits.h
+++ b/ui/gfx/mojom/ca_layer_params_mojom_traits.h
@@ -20,6 +20,10 @@ struct StructTraits<gfx::mojom::CALayerParamsDataView, gfx::CALayerParams> {
     return ca_layer_params.pixel_size;
   }
 
+  static gfx::Rect damage(const gfx::CALayerParams& ca_layer_params) {
+    return ca_layer_params.damage;
+  }
+
   static float scale_factor(const gfx::CALayerParams& ca_layer_params) {
     return ca_layer_params.scale_factor;
   }
