Share backing canvases between browser compositors.

content/browser/compositor/software_output_device_win.cc

Index: content/browser/compositor/software_output_device_win.cc
diff --git a/content/browser/compositor/software_output_device_win.cc b/content/browser/compositor/software_output_device_win.cc
index 94ceafd2ebb701aa817650d53e00f63d5d0b7b4c..4ef5957976e4acaecab6dabd719989cde6e04c0c 100644
--- a/content/browser/compositor/software_output_device_win.cc
+++ b/content/browser/compositor/software_output_device_win.cc
@@ -4,6 +4,8 @@
 
 #include "content/browser/compositor/software_output_device_win.h"
 
+#include "base/memory/shared_memory.h"
+#include "base/memory/singleton.h"
 #include "content/public/browser/browser_thread.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkDevice.h"
@@ -15,6 +17,73 @@
 
 namespace content {
 
+namespace {
+
+class SharedMemoryBacking {
+ public:
+  static SharedMemoryBacking* GetInstance() {

[piman, 2015/05/11 23:20:56]

nit: could the SharedMemoryBacking be owned by the GpuProcessTransportFactory
and passed to the SoftwareOutputDeviceWin? Avoiding globals can be helpful for
testing.

+    return Singleton<SharedMemoryBacking>::get();
+  }
+
+  void Resized() {
+    size_t new_size = GetMaxByteSize();
+    if (new_size == created_byte_size_)
+      return;
+    for (SoftwareOutputDeviceWin* device : devices_) {
+      device->ReleaseContents();
+    }
+    backing_.reset();
+    created_byte_size_ = 0;
+  }
+
+  void RegisterOutputDevice(SoftwareOutputDeviceWin* device) {
+    devices_.push_back(device);
+  }
+
+  void UnregisterOutputDevice(SoftwareOutputDeviceWin* device) {
+    auto it = std::find(devices_.begin(), devices_.end(), device);
+    DCHECK(it != devices_.end());
+    devices_.erase(it);
+    Resized();
+  }
+
+  base::SharedMemory* GetSharedMemory() {
+    if (backing_)
+      return backing_.get();
+    created_byte_size_ = GetMaxByteSize();
+
+    backing_.reset(new base::SharedMemory);
+    CHECK(backing_->CreateAnonymous(created_byte_size_));
+    return backing_.get();
+  }
+
+ private:
+  SharedMemoryBacking() : created_byte_size_(0) {}
+
+  ~SharedMemoryBacking() {
+    DCHECK(devices_.empty());
+  }
+
+  size_t GetMaxByteSize() {
+    size_t max_size = 0;
+    for (const SoftwareOutputDeviceWin* device : devices_) {
+      max_size = std::max(
+          max_size,
+          static_cast<size_t>(device->viewport_pixel_size().GetArea() * 4));
+    }
+    return max_size;
+  }
+
+  std::vector<SoftwareOutputDeviceWin*> devices_;
+  scoped_ptr<base::SharedMemory> backing_;
+  size_t created_byte_size_;
+  friend struct DefaultSingletonTraits<SharedMemoryBacking>;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedMemoryBacking);
+};
+
+}  // namespace
+
 SoftwareOutputDeviceWin::SoftwareOutputDeviceWin(ui::Compositor* compositor)
     : hwnd_(compositor->widget()),
       is_hwnd_composited_(false) {
@@ -23,10 +92,14 @@ SoftwareOutputDeviceWin::SoftwareOutputDeviceWin(ui::Compositor* compositor)
 
   LONG style = GetWindowLong(hwnd_, GWL_EXSTYLE);
   is_hwnd_composited_ = !!(style & WS_EX_COMPOSITED);
+  if (!is_hwnd_composited_)
+    SharedMemoryBacking::GetInstance()->RegisterOutputDevice(this);
 }
 
 SoftwareOutputDeviceWin::~SoftwareOutputDeviceWin() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  if (!is_hwnd_composited_)
+    SharedMemoryBacking::GetInstance()->UnregisterOutputDevice(this);
 }
 
 void SoftwareOutputDeviceWin::Resize(const gfx::Size& viewport_pixel_size,
@@ -39,19 +112,27 @@ void SoftwareOutputDeviceWin::Resize(const gfx::Size& viewport_pixel_size,
     return;
 
   viewport_pixel_size_ = viewport_pixel_size;
-  contents_.reset(new gfx::Canvas(viewport_pixel_size, 1.0f, true));
-  memset(&bitmap_info_, 0, sizeof(bitmap_info_));
-  gfx::CreateBitmapHeader(viewport_pixel_size_.width(),
-                          viewport_pixel_size_.height(),
-                          &bitmap_info_.bmiHeader);
+  if (!is_hwnd_composited_)
+    SharedMemoryBacking::GetInstance()->Resized();
+  contents_.reset();
 }
 
 SkCanvas* SoftwareOutputDeviceWin::BeginPaint(const gfx::Rect& damage_rect) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  DCHECK(contents_);
+  if (!contents_) {
+    HANDLE shared_section = NULL;
+    // Layered windows must be completely updated every time, so they can't
+    // share contents with other windows.
+    if (!is_hwnd_composited_)

[piman, 2015/05/11 23:20:56]

nit: needs {}

+      shared_section =
+          SharedMemoryBacking::GetInstance()->GetSharedMemory()->handle();
+    contents_.reset(skia::CreatePlatformCanvas(
+        viewport_pixel_size_.width(), viewport_pixel_size_.height(), true,
+        shared_section, skia::CRASH_ON_FAILURE));
+  }
 
   damage_rect_ = damage_rect;
-  return contents_ ? contents_->sk_canvas() : NULL;
+  return contents_.get();
 }
 
 void SoftwareOutputDeviceWin::EndPaint(cc::SoftwareFrameData* frame_data) {
@@ -59,9 +140,6 @@ void SoftwareOutputDeviceWin::EndPaint(cc::SoftwareFrameData* frame_data) {
   DCHECK(contents_);
   DCHECK(frame_data);
 
-  if (!contents_)
-    return;
-
   SoftwareOutputDevice::EndPaint(frame_data);
 
   gfx::Rect rect = damage_rect_;
@@ -69,8 +147,6 @@ void SoftwareOutputDeviceWin::EndPaint(cc::SoftwareFrameData* frame_data) {
   if (rect.IsEmpty())
     return;
 
-  SkCanvas* canvas = contents_->sk_canvas();
-  DCHECK(canvas);
   if (is_hwnd_composited_) {
     RECT wr;
     GetWindowRect(hwnd_, &wr);
@@ -84,16 +160,21 @@ void SoftwareOutputDeviceWin::EndPaint(cc::SoftwareFrameData* frame_data) {
     style |= WS_EX_LAYERED;
     SetWindowLong(hwnd_, GWL_EXSTYLE, style);
 
-    HDC dib_dc = skia::BeginPlatformPaint(canvas);
+    HDC dib_dc = skia::BeginPlatformPaint(contents_.get());
     ::UpdateLayeredWindow(hwnd_, NULL, &position, &size, dib_dc, &zero,
                           RGB(0xFF, 0xFF, 0xFF), &blend, ULW_ALPHA);
-    skia::EndPlatformPaint(canvas);
+    skia::EndPlatformPaint(contents_.get());
   } else {
     HDC hdc = ::GetDC(hwnd_);
     RECT src_rect = rect.ToRECT();
-    skia::DrawToNativeContext(canvas, hdc, rect.x(), rect.y(), &src_rect);
+    skia::DrawToNativeContext(contents_.get(), hdc, rect.x(), rect.y(),
+                              &src_rect);
     ::ReleaseDC(hwnd_, hdc);
   }
 }
 
+void SoftwareOutputDeviceWin::ReleaseContents() {

[piman, 2015/05/11 23:20:56]

nit: any way to DCHECK we're not between BeginPaint and EndPaint?

+  contents_.release();
+}
+
 }  // namespace content