Introducing a will-enter-full-screen event that's cancellable

atom/browser/api/atom_api_window.cc

@@ -219,6 +219,10 @@ void Window::OnWindowMoved() {
   Emit("moved");
 }
 
+void Window::OnWindowWillEnterFullScreen(bool* prevent_default) {
+  *prevent_default = Emit("will-enter-full-screen");
+}
+
 void Window::OnWindowEnterFullScreen() {
   Emit("enter-full-screen");
 }

atom/browser/api/atom_api_window.h

@@ -67,6 +67,7 @@ class Window : public mate::TrackableObject<Window>,
   void OnWindowMoved() override;
   void OnWindowScrollTouchBegin() override;
   void OnWindowScrollTouchEnd() override;
+  void OnWindowWillEnterFullScreen(bool* prevent_default) override;
   void OnWindowEnterFullScreen() override;
   void OnWindowLeaveFullScreen() override;
   void OnWindowEnterHtmlFullScreen() override;

atom/browser/native_window.cc

@@ -445,6 +445,13 @@ void NativeWindow::NotifyWindowMoved() {
   FOR_EACH_OBSERVER(NativeWindowObserver, observers_, OnWindowMoved());
 }
 
+bool NativeWindow::RequestEnterFullScreen() {
+  bool prevent_default = false;
+  FOR_EACH_OBSERVER(NativeWindowObserver, observers_,
+                    OnWindowWillEnterFullScreen(&prevent_default));
+  return prevent_default;
+}
+
 void NativeWindow::NotifyWindowEnterFullScreen() {
   FOR_EACH_OBSERVER(NativeWindowObserver, observers_,
                     OnWindowEnterFullScreen());

atom/browser/native_window.h

@@ -197,6 +197,9 @@ class NativeWindow : public base::SupportsUserData,
   // Requests the WebContents to close, can be cancelled by the page.
   virtual void RequestToClosePage();
 
+  // Request the WebContents to go fullscreen, can be cancelled by the page.
+  virtual bool RequestEnterFullScreen();
+
   // Methods called by the WebContents.
   virtual void CloseContents(content::WebContents* source);
   virtual void RendererUnresponsive(content::WebContents* source);

atom/browser/native_window_mac.mm

@@ -602,6 +602,9 @@ void NativeWindowMac::SetFullScreen(bool fullscreen) {
   if (fullscreen == IsFullscreen())
     return;
 
+  if (fullscreen && shell_->RequestEnterFullScreen())
+    return;
+
   if (!base::mac::IsOSLionOrLater()) {
     LOG(ERROR) << "Fullscreen mode is only supported above Lion";
     return;

atom/browser/native_window_observer.h

@@ -52,6 +52,7 @@ class NativeWindowObserver {
   virtual void OnWindowMoved() {}
   virtual void OnWindowScrollTouchBegin() {}
   virtual void OnWindowScrollTouchEnd() {}
+  virtual void OnWindowWillEnterFullScreen(bool* prevent_default) {}
   virtual void OnWindowEnterFullScreen() {}
   virtual void OnWindowLeaveFullScreen() {}
   virtual void OnWindowEnterHtmlFullScreen() {}

atom/browser/native_window_views.cc

@@ -347,24 +347,33 @@ bool NativeWindowViews::IsMinimized() {
 }
 
 void NativeWindowViews::SetFullScreen(bool fullscreen) {
+  bool prevent_default = false;
+  if (fullscreen)
+    prevent_default = RequestEnterFullScreen();
+
 #if defined(OS_WIN)
   // There is no native fullscreen state on Windows.
   if (fullscreen) {
-    last_window_state_ = ui::SHOW_STATE_FULLSCREEN;
-    NotifyWindowEnterFullScreen();
+    if (!prevent_default) {
+      last_window_state_ = ui::SHOW_STATE_FULLSCREEN;
+      NotifyWindowEnterFullScreen();
+    }
   } else {
     last_window_state_ = ui::SHOW_STATE_NORMAL;
     NotifyWindowLeaveFullScreen();
   }
   // We set the new value after notifying, so we can handle the size event
   // correctly.
-  window_->SetFullscreen(fullscreen);
-#else
-  if (IsVisible())
+  if (!prevent_default)
     window_->SetFullscreen(fullscreen);
-  else
-    window_->native_widget_private()->ShowWithWindowState(
-        ui::SHOW_STATE_FULLSCREEN);
+#else
+  if (!(fullscreen && prevent_default)) {
+    if (IsVisible())
+      window_->SetFullscreen(fullscreen);
+    else
+      window_->native_widget_private()->ShowWithWindowState(
+          ui::SHOW_STATE_FULLSCREEN);
+  }
 #endif
 }