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 7c6ca0c24fd53a27552363ee3117c8901020d233..06761b816c6f94d9f3da521843e125749af5df27 100644
--- a/content/browser/compositor/software_output_device_win.cc
+++ b/content/browser/compositor/software_output_device_win.cc
@@ -4,33 +4,98 @@
 
 #include "content/browser/compositor/software_output_device_win.h"
 
+#include "base/memory/shared_memory.h"
 #include "content/public/browser/browser_thread.h"
+#include "skia/ext/platform_canvas.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkDevice.h"
 #include "ui/compositor/compositor.h"
-#include "ui/gfx/canvas.h"
 #include "ui/gfx/gdi_util.h"
 #include "ui/gfx/skia_util.h"
 
 namespace content {
 
-SoftwareOutputDeviceWin::SoftwareOutputDeviceWin(ui::Compositor* compositor)
+OutputDeviceBacking::OutputDeviceBacking() : created_byte_size_(0) {
+}
+
+OutputDeviceBacking::~OutputDeviceBacking() {
+  DCHECK(devices_.empty());
+}
+
+void OutputDeviceBacking::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 OutputDeviceBacking::RegisterOutputDevice(
+    SoftwareOutputDeviceWin* device) {
+  devices_.push_back(device);
+}
+
+void OutputDeviceBacking::UnregisterOutputDevice(
+    SoftwareOutputDeviceWin* device) {
+  auto it = std::find(devices_.begin(), devices_.end(), device);
+  DCHECK(it != devices_.end());
+  devices_.erase(it);
+  Resized();
+}
+
+base::SharedMemory* OutputDeviceBacking::GetSharedMemory() {
+  if (backing_)
+    return backing_.get();
+  created_byte_size_ = GetMaxByteSize();
+
+  backing_.reset(new base::SharedMemory);
+  CHECK(backing_->CreateAnonymous(created_byte_size_));
+  return backing_.get();
+}
+
+size_t OutputDeviceBacking::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;
+}
+
+SoftwareOutputDeviceWin::SoftwareOutputDeviceWin(OutputDeviceBacking* backing,
+                                                 ui::Compositor* compositor)
     : hwnd_(compositor->widget()),
-      is_hwnd_composited_(false) {
+      is_hwnd_composited_(false),
+      backing_(backing),
+      in_paint_(false) {
   // TODO(skaslev) Remove this when crbug.com/180702 is fixed.

[piman, 2015/05/12 03:03:51]

nit: BTW you can remove this comment now, since that bug is WontFix.

   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
   LONG style = GetWindowLong(hwnd_, GWL_EXSTYLE);
   is_hwnd_composited_ = !!(style & WS_EX_COMPOSITED);
+  // Layered windows must be completely updated every time, so they can't
+  // share contents with other windows.
+  if (is_hwnd_composited_)
+    backing_ = nullptr;
+  if (backing_)
+    backing_->RegisterOutputDevice(this);
 }
 
 SoftwareOutputDeviceWin::~SoftwareOutputDeviceWin() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  DCHECK(!in_paint_);
+  if (backing_)
+    backing_->UnregisterOutputDevice(this);
 }
 
 void SoftwareOutputDeviceWin::Resize(const gfx::Size& viewport_pixel_size,
                                      float scale_factor) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  DCHECK(!in_paint_);
 
   scale_factor_ = scale_factor;
 
@@ -38,29 +103,35 @@ 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 (backing_)
+    backing_->Resized();
+  contents_.clear();
 }
 
 SkCanvas* SoftwareOutputDeviceWin::BeginPaint(const gfx::Rect& damage_rect) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  DCHECK(contents_);
+  DCHECK(!in_paint_);
+  if (!contents_) {
+    HANDLE shared_section = NULL;
+    if (backing_)
+      shared_section = backing_->GetSharedMemory()->handle();
+    contents_ = skia::AdoptRef(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;
+  in_paint_ = true;
+  return contents_.get();
 }
 
 void SoftwareOutputDeviceWin::EndPaint(cc::SoftwareFrameData* frame_data) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   DCHECK(contents_);
   DCHECK(frame_data);
+  DCHECK(in_paint_);
 
-  if (!contents_)
-    return;
-
+  in_paint_ = false;
   SoftwareOutputDevice::EndPaint(frame_data);
 
   gfx::Rect rect = damage_rect_;
@@ -68,8 +139,6 @@ 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);
@@ -83,16 +152,23 @@ 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() {
+  DCHECK(!contents_ || contents_->unique());
+  DCHECK(!in_paint_);
+  contents_.clear();
+}
+
 }  // namespace content