Merge pull request #8250 from gerhardberger/osr-window-size-fix

Always create offscreen window frameless

atom/browser/api/atom_api_window.cc

@@ -90,6 +90,13 @@ Window::Window(v8::Isolate* isolate, v8::Local<v8::Object> wrapper,
     if (options.Get("transparent", &transparent))
       web_preferences.Set("transparent", transparent);
 
+    // Offscreen windows are always created frameless.
+    bool offscreen;
+    if (web_preferences.Get("offscreen", &offscreen) && offscreen) {
+      auto window_options = const_cast<mate::Dictionary&>(options);
+      window_options.Set(options::kFrame, false);
+    }
+
     // Creates the WebContents used by BrowserWindow.
     web_contents = WebContents::Create(isolate, web_preferences);
   }

docs/tutorial/offscreen-rendering.md

@@ -12,6 +12,8 @@ when there is nothing happening on a webpage, no frames are generated. The
 maximum frame rate is 60, because above that there is no benefit, just
 performance loss.
 
+**Note:** An offscreen window is always created as a [Frameless Window](../api/frameless-window.md).
+
 ## Two modes of rendering
 
 ### GPU accelerated