DCEF3: How to get a screenshot

问题

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;

回答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.

来源：https://stackoverflow.com/questions/23755232/dcef3-how-to-get-a-screenshot

标签

Delphi

delphi-xe5

chromium-embedded

tchromium