DCEF3: How to get a screenshot

Question

How to get screenshot of browser in DCEF3?

I create browser like this without VCL. The TakePicture method will only work if

No debugger is used

If ShowWindow is used

var
  info: TCefWindowInfo;
  Settings: TCefBrowserSettings;
begin
  FillChar(info, SizeOf(info), 0);
  info.width := width;
  info.height := height;
  FillChar(Settings, SizeOf(TCefBrowserSettings), 0);
  Settings.Size := SizeOf(TCefBrowserSettings);
  GetSettings(Settings);
  CefBrowserHostCreateBrowser(@info, FHandler, FDefaultUrl, @settings, nil);
end;

procedure TakePicture(const Browser: ICefBrowser; Height, Width: Integer);
var
  DC: HDC;
  Bmp : TBitmap;
  Handle : HWND;
  Rect : trect;
  BarHeight : integer;
  BarLeft : integer;
begin
  Bmp := TBitmap.Create;
  Bmp.PixelFormat := pf32bit;
  Handle := Browser.Host.WindowHandle;
  ShowWindow(handle, SW_RESTORE); // will work only if this is used otherwise black image!
  BarLeft := GetSystemMetrics(SM_CXFRAME);
  BarHeight := GetSystemMetrics(SM_CYCAPTION) + GetSystemMetrics(SM_CYFRAME);
  GetWindowRect(Handle, Rect);
  DC := GetDC(Handle);
  Bmp.Width := Rect.Right - Rect.Left;
  Bmp.Height := (Rect.Bottom - Rect.Top);
  BitBlt(Bmp.Canvas.Handle, 0, 0, Bmp.Width, Bmp.Height, DC, -BarLeft, -BarHeight, SRCCOPY);
  ReleaseDC(Handle, DC);
  Bmp.SaveToFile('c:\test.bmp');
  Bmp.Free;
end;

Doesn't this work? http://stackoverflow.com/questions/661250/how-to-take-a-screenshot-of-the-active-window-in-delphi — Jan Doggen, May 20 '14 at 10:22
Please update your question with the actual snapshot code you are using that currently fails. — Jan Doggen, May 20 '14 at 10:32
Sorry, my mistake. It is the DCEF1 which has [`this procedure`](https://code.google.com/p/delphichromiumembedded/source/browse/trunk/src/cefvcl.pas#481)... — TLama, May 21 '14 at 15:18
I don't think so. At least, there is no `ICefBrowser::GetImage` method in CEF3. — TLama, May 21 '14 at 15:43
@TLama Could it be done with this? http://pastebin.com/dbj3MYdZ — user3655788, May 21 '14 at 15:47
In that code I can't see anything attempting to render the content to a bitmap. — TLama, May 21 '14 at 16:00
@TLama I get black image when i try to save as image. Why is this? — user3655788, May 24 '14 at 17:14

Thijs van Dien · Answer 1 · 2014-05-20T11:07:36.087

1

This is basically off-screen rendering. In the demos folder of DCEF3 you'll find a project 'offscreen'. The code you're looking for is in the OnPaint event of TChromiumOSR. It renders to a TBitmap32, but any bitmap could be made to work. Notice that it has been optimized to only paint the so-called "dirty" areas (those that have changed since last painting), but if you're making a screenshot, that's not what you want. In my check-out of the repository there's a line commented out showing the naive case of just painting everything:

SomeBitmap.SetSize(width, height);
Move(buffer^, SomeBitmap32.Bits^, width * height * 4);

It's my best guess that the magic number 4 represents 4 bytes (32-bits).

I warmly recommend using Graphics32 but it you have to use a regular TBitmap, I'll leave it up to you to work out how to turn the array of bits into pixels. Be warmed it will probably be a lot slower.

edited May 20 '14 at 11:07

answered May 20 '14 at 10:44

Thijs van Dien

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Not much help this answer. Need concrete example. – user3655788 May 20 '14 at 10:54
@user3655788 My answer basically tells you where to find the example. – Thijs van Dien May 20 '14 at 10:57
I get a black image. I doubt i need to use offscreen rendering to get a simple screenshot. Thats for firemonkey. – user3655788 May 20 '14 at 10:58
1

@user3655788 Try that demo; it works. There's not really any VCL involved there until the `TBitmap32` is rendered by the `TPaintBox32`. Have a good look at it and translate it to your own code but it basically comes down to the above. A "simple screenshot" still involves rendering the website. If you don't have it rendered to the form already (in which case you could use the link @JanDoggen provided), you'll need to render off-screen. – Thijs van Dien May 20 '14 at 11:06
@user3655788 The only problem you might run into with that demo is that you need to change `event.type_` into `event.kind` (error when compiling). – Thijs van Dien May 20 '14 at 11:11
Problem is this `OnPaint` is not even called. – user3655788 May 24 '14 at 16:21

DCEF3: How to get a screenshot

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