WPF/OffScreen require setting windowless_rendering_enabled in 67+

[amaitland]

See http://magpcss.org/ceforum/viewtopic.php?f=6&t=16077

To-do update with more details later. Just adding as placeholder

[amaitland]

See https://bitbucket.org/chromiumembedded/cef/src/514ced40ceffa16966d9dee23a253014faf74d72/libcef/browser/osr/render_widget_host_view_osr.cc?at=3396&fileviewer=file-view-default#render_widget_host_view_osr.cc-243 (only appears relevant for 3396 branch)

[joaompneves]

Probably this should be set as true by default on CefSettings?
I upgraded to the latest version and got a blank screen, because I'm doing Cef initialization with custom settings. I spent a couple of hours looking (debugging) for the problem and had to go through the list of latest changes until I found this. Setting the default to true would prevent further problems.

[amaitland]

It's not that straightforward or I would have already done it. Have a think about the problem further, open to suggestions.

[bddckr]

Isn't this already handled by the browser class trying to do it in its constructor?

CefSharp/CefSharp.OffScreen/ChromiumWebBrowser.cs

Lines 277 to 286 in 9d4504d

	if (!Cef.IsInitialized)
	{
	var settings = new CefSettings();
	settings.WindowlessRenderingEnabled = true;
	if (!Cef.Initialize(settings))
	{
	throw new InvalidOperationException("Cef::Initialize() failed");
	}
	}

This obviously fails if CEF is already initialized. How about throwing an exception from now on when CEF is initialized but the flag not being set to true (in this constructor that is)?
That would take care of blowing up in my face early, rather than me overlooking this in any changelog etc.

[amaitland]

https://bitbucket.org/chromiumembedded/cef/issues/2447/osr-add-support-for-surface

[amaitland]

Short term solution throwing an exception maybe ok, long term I'm thinking this is going to need quite a bit more work. It's becoming more common that custom command line arguments are required, #2408 is another example.

1. Make CefSettings constructor private and create some static methods, e.g. CefSettings.ForWpf() that load the custom values required for WPF. The documentation would need to be updated in a few places for this to work.
2. Change Cef.Initialize to take an abstract instance of CefSettings (would need to be renamed e.g. AbstractCefSettings) and create C# instances of CefSettings in each of the three namespaces, this would require one additional using statement in some cases, documentation would be largely unchanged.

Will probably go with option 2, won't know how exactly it's going to play out until it's implemented.

[amaitland]

Issue #2477 implements Option 2, so WindowlessRenderingEnabled will be set accordingly.

This is a minor breaking change.