CODEWITHSUNDEEP
wpfwinformscefsharp
AIJAZ HASSAN
AIJAZ HASSAN

Reputation: 13

Automation: Why WPF based CEFSharp uses Bitmap for rendering while winforms does not?

We were able to use automation tool and it was able to identify html objects on Winforms while on WPF it does not since it is rendered as an image.

My main question is what does Winform CEFSharp uses to render and why WPF not able to use a similar rendering mechanism?

Upvotes: 1

Views: 1103

Answers (1)

quetzalcoatl
quetzalcoatl

Reputation: 33546

Warning: it is a very generic answer. I briefly looked at CEF source (briefly - 3-5 minutes) and the rest are my guesses based on my own WPF/WinForms interop experiences. I've had quite a few. I also played a bit with early Chromium builds. However, all of that was a few years ago, so it may simply be out dated. Maybe Chromium has now first-class WPF support. I have not found any information about that, but if this really happened, I encourage you even stronger to follow the last paragraph.

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I doubt that there is any reason behind this other than time-cost to implement - either on CEF or Chromium project.

WinForms and WPF are totally different GUI frameworks, written in different eras, using different architectures, different rendering techniques, different platform features, etc. This is as different as it can be, down to the idea of a "Window" itself.

In WinForms, almost every control is a separate small window-like thing, has a system-wide handle, has a system-tracked region, etc. All controls render themselves almost directly by unmanaged win32 GDI+ functions.

In WPF they don't. In WPF there's only one handle per whole window, controls don't render themselves. Instead they have a definition of their "look" and the WPF renders them to the 'surface', which is then blitted/streamed (sorry, dont remember) to target device.

That's true that CEF uses different approaches. For WinForms they make heavy use of a 'browser component' taken directly from Chromium, for WPF they render to bitmap and show/update the bitmap periodically.

Why? My guess is that it's because Chromium already provided a COM/OCX/ActiveX/whatever component, and WinForms can use it almost directly, thanks to the everything-has-a-handle "feature" - if you can call it a feature - one of the goals and successes of WPF was to eliminate that.

However, I don't think that Chromium at that point of time provides any such component for WPF.

If it does not exist, then for WPF there are only two options - one could embed the WinForms component in WPF window through a special 'host' intermediate control, but that actually hits the performance and also has many problems when some advanced rendering features (like movie streaming) are used. Diagnosing and fixing them is complex, hard, and even unstable (crosshosted components behave very differently on different windows and .net versions, even on .net patches sometimes change them, it can work one one, and freeze on other, hang and render as black on next and cause a blue-screen on another)

Other option for WPF is to use the "offscreen" mode. Chromium can render to a bitmap, so why not. Render to bitmap, and display that. Simple. Quick. No problems.

So, I'd say, it all boils down to a famous quote from Eric Lippert:

The question is "why does [snip] not have this feature?" The answer to that question is always the same. Features are unimplemented by default; [snip] does not have that feature because no one designed, implemented and shipped the feature to customers.

It's great we can at least display Chromium in WPF apps. If you think it can be done better and that it's worth doing, it's open source, feel free to implement it - if not in CEF, then in Chromium itself.

Upvotes: 1

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