BitBlt and ElementHost not working on some machines

Question

This is a weird problem.

I'm using BitBlt to copy from the device context associated with my (WinForms) window handle to a bitmap, and it works (or so I thought).

But there's one machine where the WPF elements inside ElementHost just don't show up on the bitmap: there isn't a hole, it's just as if they were transparent and whatever is behind appears instead.

I've been playing around with one VM, one working and the other not. They both have the same OS version, I've whittled down the installed Programs and Features to be the same on both, and yet there is still one which works and the other not.

Has anyone come across this problem, and does anyone have any ideas where to start searching?

UPDATE: thanks to jsanalytics tip in the comment, I've worked out that it's Aero which stops the screenshot working properly. Now to work out why and what to do about it...

Take a look [HERE](https://stackoverflow.com/questions/47801997/bitblt-screen-capture-not-working-on-windows-10#comment82864127_47801997). I had suggested `GetLastWin32Error()` but never heard back from OP. — jsanalytics, Jan 17 '18 at 10:44
@jsanalytics, thanks. So I can confirm that it's Aero which makes the difference (off = works, on = doesn't work). — Benjol, Jan 17 '18 at 10:54
Just one more thing: I'm assuming you got error code zero in the machine it does **not** work, right? — jsanalytics, Jan 17 '18 at 11:28
@jsanalytics, yes. [This guy](https://stackoverflow.com/a/24816975/11410) seems to have had the same problem. I'm going to try disabling DWM. — Benjol, Jan 17 '18 at 11:31
That doesn't work either. Monster screen flicker and black image... — Benjol, Jan 17 '18 at 11:37

score 1 · Answer 1 · answered Jan 17 '18 at 13:54

This isn't the answer, but it's working for me for the moment:

If

[DllImport("dwmapi.dll", PreserveSig = false)]
public static extern int DwmIsCompositionEnabled(out bool enabled);

Returns true, then instead of BitBlting the Device context of the window, I BitBlt the whole desktop, but crop to the size of the window (using GetWindowRect and adapting the created Bitmap to the size, then passing left and top into BitBlt).

BitBlt and ElementHost not working on some machines

1 Answers1