Merge pull request #6026 from electron/ready-to-show

Add "ready-to-show" event and docs on showing window gracefully

atom/browser/api/atom_api_window.cc

@@ -156,6 +156,10 @@ void Window::OnWindowHide() {
   Emit("hide");
 }
 
+void Window::OnReadyToShow() {
+  Emit("ready-to-show");
+}
+
 void Window::OnWindowMaximize() {
   Emit("maximize");
 }

atom/browser/api/atom_api_window.h

@@ -61,6 +61,7 @@ class Window : public mate::TrackableObject<Window>,
   void OnWindowFocus() override;
   void OnWindowShow() override;
   void OnWindowHide() override;
+  void OnReadyToShow() override;
   void OnWindowMaximize() override;
   void OnWindowUnmaximize() override;
   void OnWindowMinimize() override;

atom/browser/native_window.cc

@@ -560,6 +560,22 @@ void NativeWindow::BeforeUnloadDialogCancelled() {
   window_unresposive_closure_.Cancel();
 }
 
+void NativeWindow::DidFirstVisuallyNonEmptyPaint() {
+  if (IsVisible())
+    return;
+
+  // When there is a non-empty first paint, resize the RenderWidget to force
+  // Chromium to draw.
+  const auto view = web_contents()->GetRenderWidgetHostView();
+  view->Show();
+  view->SetSize(GetContentSize());
+
+  // Emit the ReadyToShow event in next tick in case of pending drawing work.
+  base::MessageLoop::current()->PostTask(
+      FROM_HERE,
+      base::Bind(&NativeWindow::NotifyReadyToShow, GetWeakPtr()));
+}
+
 bool NativeWindow::OnMessageReceived(const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(NativeWindow, message)
@@ -601,6 +617,10 @@ void NativeWindow::NotifyWindowUnresponsive() {
                       OnRendererUnresponsive());
 }
 
+void NativeWindow::NotifyReadyToShow() {
+  FOR_EACH_OBSERVER(NativeWindowObserver, observers_, OnReadyToShow());
+}
+
 void NativeWindow::OnCapturePageDone(const CapturePageCallback& callback,
                                      const SkBitmap& bitmap,
                                      content::ReadbackResponse response) {

atom/browser/native_window.h

@@ -275,6 +275,7 @@ class NativeWindow : public base::SupportsUserData,
   // content::WebContentsObserver:
   void RenderViewCreated(content::RenderViewHost* render_view_host) override;
   void BeforeUnloadDialogCancelled() override;
+  void DidFirstVisuallyNonEmptyPaint() override;
   bool OnMessageReceived(const IPC::Message& message) override;
 
  private:
@@ -284,6 +285,9 @@ class NativeWindow : public base::SupportsUserData,
   // Dispatch unresponsive event to observers.
   void NotifyWindowUnresponsive();
 
+  // Dispatch ReadyToShow event to observers.
+  void NotifyReadyToShow();
+
   // Called when CapturePage has done.
   void OnCapturePageDone(const CapturePageCallback& callback,
                          const SkBitmap& bitmap,

atom/browser/native_window_observer.h

@@ -48,6 +48,9 @@ class NativeWindowObserver {
   // Called when window is hidden.
   virtual void OnWindowHide() {}
 
+  // Called when window is ready to show.
+  virtual void OnReadyToShow() {}
+
   // Called when window state changed.
   virtual void OnWindowMaximize() {}
   virtual void OnWindowUnmaximize() {}

docs/api/browser-window.md

@@ -4,22 +4,60 @@
 
 ```javascript
 // In the main process.
-const {BrowserWindow} = require('electron');
+const {BrowserWindow} = require('electron')
 
 // Or in the renderer process.
-const {BrowserWindow} = require('electron').remote;
+const {BrowserWindow} = require('electron').remote
 
-let win = new BrowserWindow({width: 800, height: 600, show: false});
+let win = new BrowserWindow({width: 800, height: 600})
 win.on('closed', () => {
-  win = null;
-});
+  win = null
+})
 
-win.loadURL('https://github.com');
-win.show();
+win.loadURL('https://github.com')
 ```
 
-You can also create a window without chrome by using
-[Frameless Window](frameless-window.md) API.
+## Frameless window
+
+To create a window without chrome, or a transparent window in arbitrary shape,
+you can use the [Frameless Window](frameless-window.md) API.
+
+## Showing window gracefully
+
+When loading a page in window directly, users will see the progress of loading
+page, which is not good experience for native app. To make the window display
+without visual flash, there are two solutions for different situations.
+
+### Using `ready-to-show` event
+
+While loading the page, the `ready-to-show` event will be emitted when renderer
+process has done drawing for the first time, showing window after this event
+will have no visual flash:
+
+```javascript
+let win = new BrowserWindow({show: false})
+win.once('ready-to-show', () => {
+  win.show()
+})
+```
+
+This is event is usually emitted after the `did-finish-load` event, but for
+pages with many remote resources, it may be emitted before the `did-finish-load`
+event.
+
+### Setting `backgroundColor`
+
+For a complex app, the `ready-to-show` event could be emitted too late, making
+the app feel slow. In this case, it is recommended to show the window
+immediately, and use a `backgroundColor` close to your app's background:
+
+```javascript
+let win = new BrowserWindow({backgroundColor: '#2e2c29'})
+win.loadURL('https://github.com')
+```
+
+Note that even for apps that use `ready-to-show` event, it is still recommended
+to set `backgroundColor` to make app feel more native.
 
 ## Class: BrowserWindow
 
@@ -271,6 +309,11 @@ Emitted when the window is shown.
 
 Emitted when the window is hidden.
 
+### Event: 'ready-to-show'
+
+Emitted when the web page has been rendered and window can be displayed without
+visual flash.
+
 ### Event: 'maximize'
 
 Emitted when window is maximized.