可以截取layered窗口(包括透明窗口)的代码:

procedure CaptureScreen(AFileName: string);
const
  CAPTUREBLT = $40000000;
var
  hdcScreen: HDC;
  hdcCompatible: HDC;
  bmp: TBitmap;
  hbmScreen: HBITMAP;
begin
  hdcScreen := CreateDC('DISPLAY', nil, nil, nil);
  hdcCompatible := CreateCompatibleDC(hdcScreen);
  hbmScreen := CreateCompatibleBitmap(hdcScreen,
    GetDeviceCaps(hdcScreen, HORZRES),
    GetDeviceCaps(hdcScreen, VERTRES));
  SelectObject(hdcCompatible, hbmScreen);
  bmp := TBitmap.Create;
  bmp.Handle := hbmScreen;
  BitBlt(hdcCompatible,
    0, 0,
    bmp.Width, bmp.Height,
    hdcScreen,
    0, 0,
    SRCCOPY or CAPTUREBLT);

  bmp.SaveToFile(AFileName);
  bmp.Free;
  DeleteDC(hdcScreen);
  DeleteDC(hdcCompatible);
end;

DX Primary Surface截图代码!包含DX8与DX9两个版本

...
interface

{$DEFINE D3D9}

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Buttons,
{$IFDEF D3D9}
  // D3DX9, // use D3D to save surface
  Direct3D9
{$ELSE}
  // D3DX8, // use D3D to save surface
  Direct3D8
{$ENDIF};
...
procedure TForm1.BitBtn1Click(Sender: TObject);
// Capture screen through D3D.
var
  BitsPerPixel: Byte;
  {$IFDEF D3D9}
  pD3D: IDirect3D9;
  pSurface: IDirect3DSurface9;
  g_pD3DDevice: IDirect3DDevice9;
  {$ELSE}
  pD3D: IDirect3D8;
  pSurface: IDirect3DSurface8;
  g_pD3DDevice: IDirect3DDevice8;
  {$ENDIF}
  D3DPP: TD3DPresentParameters;
  ARect: TRect;
  LockedRect: TD3DLockedRect;
  BMP: TBitmap;
  i, p: Integer;
begin
  BitsPerPixel := GetDeviceCaps(Canvas.Handle, BITSPIXEL);
  FillChar(d3dpp, SizeOf(d3dpp), 0);
  D3DPP.Windowed := True;
  D3DPP.Flags := D3DPRESENTFLAG_LOCKABLE_BACKBUFFER;
  D3DPP.SwapEffect := D3DSWAPEFFECT_DISCARD;
  D3DPP.BackBufferWidth := Screen.Width;
  D3DPP.BackBufferHeight := Screen.Height;
  D3DPP.BackBufferFormat := D3DFMT_X8R8G8B8;
  {$IFDEF D3D9}
  pD3D := Direct3DCreate9(D3D_SDK_VERSION);
  pD3D.CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, GetDesktopWindow,
    D3DCREATE_SOFTWARE_VERTEXPROCESSING, @D3DPP, g_pD3DDevice);
  g_pD3DDevice.CreateOffscreenPlainSurface(Screen.Width, Screen.Height, D3DFMT_A8R8G8B8, D3DPOOL_SCRATCH, pSurface, nil);
  g_pD3DDevice.GetFrontBufferData(0, pSurface);
  {$ELSE}
  pD3D := Direct3DCreate8(D3D_SDK_VERSION);
  pD3D.CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_REF, GetDesktopWindow,
    D3DCREATE_SOFTWARE_VERTEXPROCESSING, D3DPP, g_pD3DDevice);
  g_pD3DDevice.CreateImageSurface(Screen.Width, Screen.Height, D3DFMT_A8R8G8B8, pSurface);
  g_pD3DDevice.GetFrontBuffer(pSurface);
  {$ENDIF}
  // use D3D to save surface. Notes: D3DX%ab.dll is required!
//  D3DXSaveSurfaceToFile('Desktop.bmp', D3DXIFF_BMP, pSurface, nil,  nil);
  // use Bitmap to save surface
  ARect := Screen.DesktopRect;
  pSurface.LockRect(LockedRect, @ARect, D3DLOCK_NO_DIRTY_UPDATE or D3DLOCK_NOSYSLOCK or D3DLOCK_READONLY);
  BMP := TBitmap.Create;
  BMP.Width := Screen.Width;
  BMP.Height := Screen.Height;
  case BitsPerPixel of
    8:  BMP.PixelFormat := pf8bit;
    16: BMP.PixelFormat := pf16bit;
    24: BMP.PixelFormat := pf24bit;
    32: BMP.PixelFormat := pf32bit;
  end;
  p := Cardinal(LockedRect.pBits);
  for i := 0 to Screen.Height - 1 do
    begin
      CopyMemory(BMP.ScanLine[i], Ptr(p), Screen.Width * BitsPerPixel div 8);
      p := p + LockedRect.Pitch;
    end;
  BMP.SaveToFile('Desktop.bmp');
  BMP.Free;
  pSurface.UnlockRect;
end;

以上DX截图代码,不需要额外的DLL支持,有DirectX 9.0即可

采用上面的2个方案以外,还有些视频播放器的图像不能截取吧,呵呵

怎么解决呢?

它们使用的,是称为"覆盖表面"的技术,截取覆盖表面,需要Hook的手段才行

思路是:
通过Hook DDraw的DirectDrawCreate(RealOne用)同DirectDrawCreateEx(WMP用)
获得IDirectDraw(7)
再COM Hook CreateSurface,注意RealOne使用的是通过QueryInterface获得IDirectDraw2
WMP则是IDirectDraw7

Hook了CreateSurface后,就能获得OverlaySurface

所以必须在软件使用前,启动全局Hook,才有效

在需要截图的时候
Lock Overlay Surface,读取数据,马上Unlock,以免损失性能

解码读出来的数据,即可,但是由于获得的数据是显卡硬件VRAM的数据,一般是YUY2,YV12等格式,需要转换为RGB格式

例如,在我的GF6600上,RealOne(RMVB)用的是YUY2,而WMP(AVI)用的是YV12,还与当前播放的文件格式有关

提供主表面截图源码和覆盖表面截图的测试程序http://lysoft.lz169.com/projects/DXCapture.rar
现在支持YV12,NV12,YUY2,UUVY 4个格式