adds docs for osr

atom/browser/api/atom_api_web_contents.cc

@@ -1396,8 +1396,8 @@ void WebContents::OnPaint(
   v8::MaybeLocal<v8::Object> buffer = node::Buffer::New(isolate
     , (char *)bitmap_pixels, sizeof(bitmap_pixels));
 
-  Emit("paint", damage_rect, bitmap_width, bitmap_height,
+  const gfx::Size bitmap_size = gfx::Size(bitmap_width, bitmap_height);
-       buffer.ToLocalChecked());
+  Emit("paint", damage_rect, buffer.ToLocalChecked(), bitmap_size);
 }
 
 void WebContents::StartPainting() {

atom/browser/osr_render_widget_host_view_mac.mm

@@ -4,17 +4,10 @@
 
 #include "atom/browser/osr_render_widget_host_view.h"
 
-#include <algorithm>
-#include <limits>
-#include <utility>
-
 #import <Cocoa/Cocoa.h>
 
-#include "base/compiler_specific.h"
 #include "base/strings/utf_string_conversions.h"
-#include "content/common/view_messages.h"
 #include "ui/accelerated_widget_mac/accelerated_widget_mac.h"
-#include "ui/events/latency_info.h"
 
 ui::AcceleratedWidgetMac* atom::OffScreenRenderWidgetHostView::GetAcceleratedWidgetMac()
     const {

atom/browser/web_contents_preferences.cc

@@ -189,8 +189,6 @@ void WebContentsPreferences::AppendExtraCommandLineSwitches(
 
   command_line->AppendSwitch(cc::switches::kEnableBeginFrameScheduling);
   command_line->AppendSwitch(cc::switches::kShowFPSCounter);
-  // command_line->AppendSwitch("disable-gpu");
-  // command_line->AppendSwitch("disable-gpu-compositing");
 }
 
 // static

docs/api/browser-window.md

@@ -274,6 +274,8 @@ The `webPreferences` option is an object that can have the following properties:
 * `defaultEncoding` String - Defaults to `ISO-8859-1`.
 * `backgroundThrottling` Boolean - Whether to throttle animations and timers
   when the page becomes background. Defaults to `true`.
+* `offscreen` Boolean - Whether to enable offscreen rendering for the browser
+  window. Defaults to `false`.
 
 ### Instance Events
 

docs/api/chrome-command-line-switches.md

@@ -174,6 +174,36 @@ logging level for all code in the source files under a `foo/bar` directory.
 
 This switch only works when `--enable-logging` is also passed.
 
+## --disable-gpu
+
+Disables the use of the GPU in the renderer process. If this is set with the
+`--disable-gpu-compositing` switch, *offscreen rendering* will use a software
+output device, which has much better overall performance but lacks of WebGL
+and 3D CSS support.
+
+## --disable-gpu-compositing
+
+Disables the use of the GPU compositing in the renderer process. This should be
+set with the `--disable-gpu` switch for *offscreen rendering*.
+
+``` javascript
+const {app, BrowserWindow} = require('electron');
+
+app.commandLine.appendSwitch('disable-gpu');
+app.commandLine.appendSwitch('disable-gpu-compositing');
+
+let win = new BrowserWindow({
+  webPreferences: {
+    offscreen: true
+  }
+});
+win.loadURL('http://github.com');
+
+win.webContents.on('paint', (event, dirty, data) => {
+  updateBitmap(dirty, data);
+});
+```
+
 [app]: app.md
 [append-switch]: app.md#appcommandlineappendswitchswitch-value
 [ready]: app.md#event-ready

docs/api/web-contents.md

@@ -452,6 +452,41 @@ app.on('ready', () => {
 
 Emitted when a page's view is repainted.
 
+#### Event: 'paint'
+
+Returns:
+
+* `event` Event
+* `dirtyRect` Object
+  * `x` Number - the x coordinate on the bitmap
+  * `y` Number - the y coordinate on the bitmap
+  * `width` Number - the width of the dirty area
+  * `height` Number - the height of the dirty area
+* `data` Buffer - the bitmap data of the dirty rect
+* `bitmapSize` Object
+  * `width` Number - the width of the whole bitmap
+  * `height` Number - the height of the whole bitmap
+
+Emitted when a new frame is generated. Only the dirty area is passed in the
+buffer.
+
+```javascript
+const {BrowserWindow} = require('electron');
+
+let win = new BrowserWindow({
+  width: 800,
+  height: 1500,
+  webPreferences: {
+    offscreen: true
+  }
+});
+win.loadURL('http://github.com');
+
+win.webContents.on('paint', (event, dirty, data) => {
+  updateBitmap(dirty, data);
+});
+```
+
 ### Instance Methods
 
 #### `contents.loadURL(url[, options])`
@@ -1024,6 +1059,27 @@ win.webContents.on('did-finish-load', () => {
 
 Shows pop-up dictionary that searches the selected word on the page.
 
+#### `contents.startPainting()`
+
+If *offscreen rendering* is enabled and not painting, start painting.
+
+#### `contents.stopPainting()`
+
+If *offscreen rendering* is enabled and painting, stop painting.
+
+#### `contents.isPainting()`
+
+If *offscreen rendering* is enabled returns whether it is currently painting.
+
+#### `contents.setFrameRate(fps)`
+
+If *offscreen rendering* is enabled sets the frame rate to the specified number.
+Only values between 1 and 60 are accepted.
+
+#### `contents.getFrameRate()`
+
+If *offscreen rendering* is enabled returns the current frame rate.
+
 ### Instance Properties
 
 #### `contents.id`