setOffscreenRender and api docs added

atom/browser/api/atom_api_window.cc

@@ -440,6 +440,10 @@ void Window::CapturePage(mate::Arguments* args) {
       rect, base::Bind(&OnCapturePageDone, args->isolate(), callback));
 }
 
+void Window::SetOffscreenRender(bool isOffscreen) {
+  window_->SetOffscreenRender(isOffscreen);
+}
+
 void Window::SetProgressBar(double progress) {
   window_->SetProgressBar(progress);
 }
@@ -602,6 +606,7 @@ void Window::BuildPrototype(v8::Isolate* isolate,
 #if defined(OS_MACOSX)
       .SetMethod("showDefinitionForSelection",
                  &Window::ShowDefinitionForSelection)
+      .SetMethod("setOffscreenRender", &Window::SetOffscreenRender)
 #endif
       .SetProperty("id", &Window::ID, true)
       .SetProperty("webContents", &Window::WebContents, true)

atom/browser/api/atom_api_window.h

@@ -138,6 +138,7 @@ class Window : public mate::TrackableObject<Window>,
   void SetMenuBarVisibility(bool visible);
   bool IsMenuBarVisible();
   void SetAspectRatio(double aspect_ratio, mate::Arguments* args);
+  void SetOffscreenRender(bool isOffscreen);
 
 #if defined(OS_MACOSX)
   void ShowDefinitionForSelection();

atom/browser/native_window.cc

@@ -330,6 +330,29 @@ void NativeWindow::CapturePage(const gfx::Rect& rect,
       kBGRA_8888_SkColorType);
 }
 
+void NativeWindow::SetOffscreenRender(bool isOffscreen) {
+  if (!isOffscreen && !offscreen_) return;
+
+  const auto view = web_contents()->GetRenderWidgetHostView();
+
+  if (view) {
+    if (isOffscreen) {
+      scoped_ptr<content::RenderWidgetHostViewFrameSubscriber> subscriber(
+        new RenderSubscriber(
+          view->GetVisibleViewportSize(),
+          base::Bind(&NativeWindow::OnFrameReceived, base::Unretained(this))
+        )
+      );
+
+      view->BeginFrameSubscription(subscriber.Pass());
+    } else {
+      view->EndFrameSubscription();
+    }
+
+    offscreen_ = isOffscreen;
+  }
+}
+
 void NativeWindow::RequestToClosePage() {
   bool prevent_default = false;
   FOR_EACH_OBSERVER(NativeWindowObserver,
@@ -548,15 +571,7 @@ void NativeWindow::DevToolsClosed() {
 }
 
 void NativeWindow::RenderViewReady(){
-  if(offscreen_){
-    const auto view = web_contents()->GetRenderWidgetHostView();
-
-    scoped_ptr<content::RenderWidgetHostViewFrameSubscriber> subscriber(new RenderSubscriber(
-      view->GetVisibleViewportSize(), base::Bind(&NativeWindow::OnFrameReceived, base::Unretained(this))
-    ));
-
-    view->BeginFrameSubscription(subscriber.Pass());
-  }
+  SetOffscreenRender(offscreen_);
 }
 
 void NativeWindow::RenderViewCreated(
@@ -636,7 +651,8 @@ void NativeWindow::OnCapturePageDone(const CapturePageCallback& callback,
   callback.Run(bitmap);
 }
 
-void NativeWindow::OnFrameReceived(bool result, scoped_refptr<media::VideoFrame> frame) {
+void NativeWindow::OnFrameReceived(bool result,
+                                   scoped_refptr<media::VideoFrame> frame) {
   if (result) {
     gfx::Rect rect = frame->visible_rect();
 
@@ -660,7 +676,8 @@ void NativeWindow::OnFrameReceived(bool result, scoped_refptr<media::VideoFrame>
   }
 }
 
-bool RenderSubscriber::ShouldCaptureFrame(const gfx::Rect& damage_rect,
+bool RenderSubscriber::ShouldCaptureFrame(
+                        const gfx::Rect& damage_rect,
                         base::TimeTicks present_time,
                         scoped_refptr<media::VideoFrame>* storage,
                         DeliverFrameCallback* callback) {

atom/browser/native_window.h

@@ -162,6 +162,9 @@ class NativeWindow : public content::WebContentsObserver,
   virtual void CapturePage(const gfx::Rect& rect,
                            const CapturePageCallback& callback);
 
+  // Offscreen render
+  virtual void SetOffscreenRender(bool isOffscreen);
+
   // Show popup dictionary.
   virtual void ShowDefinitionForSelection();
 
@@ -326,7 +329,10 @@ class NativeWindow : public content::WebContentsObserver,
 
 class RenderSubscriber : public content::RenderWidgetHostViewFrameSubscriber {
  public:
-  RenderSubscriber(gfx::Size size, base::Callback<void(bool, scoped_refptr<media::VideoFrame>)> callback) : size_(size), callback_(callback) {}
+  RenderSubscriber(
+    gfx::Size size,
+    base::Callback<void(bool, scoped_refptr<media::VideoFrame>)> callback)
+      : size_(size), callback_(callback) { }
 
   bool ShouldCaptureFrame(const gfx::Rect& damage_rect,
                           base::TimeTicks present_time,
@@ -335,7 +341,8 @@ class RenderSubscriber : public content::RenderWidgetHostViewFrameSubscriber {
 
   base::TimeTicks last_present_time() const { return last_present_time_; }
 
-  static void CallbackMethod(base::Callback<void(bool, scoped_refptr<media::VideoFrame>)> callback,
+  static void CallbackMethod(
+    base::Callback<void(bool, scoped_refptr<media::VideoFrame>)> callback,
     scoped_refptr<media::VideoFrame> frame,
     base::TimeTicks present_time,
     bool success) {

docs/api/browser-window.md

@@ -74,6 +74,8 @@ You can also create a window without chrome by using
     Linux.
   * `standard-window` Boolean - Uses the OS X's standard window instead of the
     textured window. Defaults to `true`.
+  * `offscreen-render` Boolean - The frame of the window will be accessible
+    through the `frame-rendered` event in a buffer. Defaults to `false`.
   * `web-preferences` Object - Settings of web page's features
     * `javascript` Boolean
     * `web-security` Boolean - When setting `false`, it will disable the same-origin
@@ -226,6 +228,15 @@ Emitted when devtools is closed.
 
 Emitted when devtools is focused / opened.
 
+### Event: 'frame-rendered'
+
+* `event` Event
+* `frame` Buffer
+* `size` Number
+
+Emitted when *offscreen render* is enabled, the current frame's pixel data
+and size are available.
+
 ### Event: 'app-command':
 
 Emitted when an [App Command](https://msdn.microsoft.com/en-us/library/windows/desktop/ms646275(v=vs.85).aspx) is invoked. These are typically related to keyboard media keys or browser commands, as well as the "Back" button built into some mice on Windows.
@@ -721,6 +732,11 @@ Returns whether the window is visible on all workspaces.
 
 **Note:** This API always returns false on Windows.
 
+### BrowserWindow.setOffscreenRender(isOffscreen)
+
+Sets the offscreen rendering, if `true` the `frame-rendered` event will fire,
+when the frame changes.
+
 ## Class: WebContents
 
 A `WebContents` is responsible for rendering and controlling a web page.