docs: Transparent window

docs/api/browser-window.md

@@ -66,6 +66,7 @@ You can also create a window without chrome by using
     scripts run in the window. This script will always have access to node APIs
     no matter whether node integration is turned on for the window, and the path
     of `preload` script has to be absolute path.
+  * `transparent` Boolean - Makes the window [transparent](frameless-window.md)
   * `web-preferences` Object - Settings of web page's features
     * `javascript` Boolean
     * `web-security` Boolean

docs/api/frameless-window.md

@@ -13,6 +13,31 @@ var BrowserWindow = require('browser-window');
 var win = new BrowserWindow({ width: 800, height: 600, frame: false });
 ```
 
+## Transparent window
+
+By setting the `transparent` option to `true`, you can also make the frameless
+window transparent:
+
+```javascript
+var win = new BrowserWindow({ transparent: true, frame: false });
+```
+
+### Limitations
+
+* You can not click through the transparent area, we are going to introduce an
+  API to set window shape to solve this, but currently blocked at an
+  [upstream bug](https://code.google.com/p/chromium/issues/detail?id=387234).
+* Transparent window is not resizable, setting `resizable` to `true` may make
+  transprent window stop working on some platforms.
+* The `blur` filter only applies to the web page, so there is no way to apply
+  blur effect to the content bellow the window.
+* On Windows transparent window will not work when DWM is disabled.
+* On Linux users have to put `--enable-transparent-visuals --disable-gpu` in
+  command line to disable GPU and allow ARGB to make transparent window, this is
+  caused by an upstream bug that [alpha channel doesn't work on some NVidia
+  drivers](https://code.google.com/p/chromium/issues/detail?id=369209) on Linux.
+* On Mac the native window shadow will not show for transparent window.
+
 ## Draggable region
 
 By default, the frameless window is non-draggable. Apps need to specify