Support for off-screen rendering

[Spk]

Hello! CEF seems to be a very nice and clean wrapper!

Is it possible to use CEF for offscreen rendering of web pages? I would like to use this in my game engine by rendering web pages to a texture in memory. I haven't seen any exposed methods to access the rendered page's bitmap data, but I suppose it would be possible to access the browser window's HDC and copy its content to a texture.

Also, the latest binaries listed in your download section are for revision 27 (june) but on your main page you mention revision 37 being available. I'd like to avoid having to recompile both chromium and CEF to get the last version so I was wondering if there might be a downloadable version of revision 37 available for lazy people like myself

Thanks in advance!

[magreenblatt]

It should be possible to use CEF for in-memory rendering with some minor changes. The implementation would be variant of how we currently handle printing. Can you give me more information about how you'd like the interface to look? For instance, is rendering to a client-provided HDC sufficient? How would you want to handle pagination and scaling?

I'm planning to provide a new binary release in the next few days, but it likely won't contain this feature since the implementation doesn't exist yet . If you download and build the source you can help develop it, which will mean you'll get it that much faster .

Regards,
Marshall

[heshiming]

There is a project named "awesomium" you might be interested. http://princeofcode.com/awesomium.php

It's also based on chromium, I suppose it used testshell in the beginning too. I haven't look at its implementation details yet. But it looks like it's primary objective is off-screen rendering.

[magreenblatt]

A new binary distribution (rev 42) is now available for download:
http://code.google.com/p/chromiumembedd ... loads/list

[jacadcaps]

A new binary distribution (rev 42) is now available for download:
http://code.google.com/p/chromiumembedd ... loads/list

Are there any examples of off-screen rendering anywhere in the project ?

[speps]

Support for rendering to an offscreen buffer would be really great, with something close to the WebView::Render function of Awesomium. The problem of Awesomium is that it is limited in terms of events and notifications and is closed source.

Here is this Render function for reference :

Code: Select all

   /**
   * Renders the WebView to an off-screen buffer.
   *
   * @param   destination   The buffer to render to, its width and height should match the WebView's.
   *
   * @param   destRowSpan   The row-span of the destination buffer (number of bytes per row).
   *
   * @param   destDepth   The depth (bytes per pixel) of the destination buffer. Valid options
   *                  include 3 (BGR/RGB) or 4 (BGRA/RGBA).
   *
   * @param   renderedRect   Optional (pass 0 to ignore); if asynchronous rendering is not enabled,
   *                     you can provide a pointer to a Rect to store the dimensions of the
   *                     rendered area, or rather, the dimensions of the area that actually
   *                     changed since the last render.
   */
   void render(unsigned char* destination, int destRowSpan, int destDepth, Awesomium::Rect* renderedRect = 0);

[Jusas]

I'd like to take a crack at it but being new to Chromium & CEF code I have no idea where to start. Any pointers?

Basically what I'm thinking is:
- Injecting input events to CEF (mouse, keyboard)
- Rendering (or copying the rendered result) to a given memory buffer (RGB/RGBA) instead of a HWND

Very simple changes, perhaps even doable as a wrapper?

[Jusas]

I'll take that back - the platform specific code seems to be rather strongly integrated into the system. HWNDs everywhere and that seems how the test_shell app was designed, it has platform specific webwidget_host_win.cc, webwidget_host_gtk.cc etc. and taking away all the platform specific code wouldn't be practical.

So... I'm guessing the best way to go would be to let CEF draw into a hidden window and then copy the HDC contents to where ever it needs to go.

[cgravill]

I've got an instance of a CEF browser running and am able to extract the image and copy it on-demand to my surface. There are the various notifications for browser-type events I can register for in my CefHandler. What I'm looking for is a notification when CEF has just redrawn so I can extract it without having to resort to a timer, a dirty region would be a bonus! Is there such a notification or way to get it?

For the initial prototype we're OK with rendering to a client-provided HDC, though if we could render direct to the image or texture that would save on processing.

Thanks,

Colin

[jerryprez]

Hi Colin,
Could you please post the code snippets or explain how you can extract rendered image of a CEF browser?

Thank you!