问从缩略图提供商(Windows)获取位图

EN

function LoadBitmapWithShellExtension(const ADllFileName: UnicodeString; const ACLSID: TCLSID;
  const AFileName: UnicodeString; ASize: Integer; out AAlpha: WTS_ALPHATYPE): HBITMAP;
type
  TDllGetClassObject = function(const CLSID, IID: TGUID; out Obj): HRESULT; stdcall;
var
  DllModule: HMODULE;
  DllGetClassObject: TDllGetClassObject;
  ClassFactory: IClassFactory;
  ThumbnailProvider: IThumbnailProvider;
  InitializeWithFile: IInitializeWithFile;
  PersistFile: IPersistFile;
begin
  DllModule := LoadLibraryW(PWideChar(ADllFileName));
  if DllModule = 0 then RaiseLastOSError;
  try
    @DllGetClassObject := GetProcAddress(DllModule, 'DllGetClassObject');
    if not Assigned(DllGetClassObject) then
      RaiseLastOSError;
    OleCheck(DllGetClassObject(ACLSID, IClassFactory, ClassFactory));
    try
      OleCheck(ClassFactory.CreateInstance(nil, IThumbnailProvider, ThumbnailProvider));
      try
        if Succeeded(ThumbnailProvider.QueryInterface(IInitializeWithFile, InitializeWithFile)) then
          try
            OleCheck(InitializeWithFile.Initialize(PWideChar(AFileName), STGM_READ));
          finally
            InitializeWithFile := nil;
          end
        else
          if Succeeded(ThumbnailProvider.QueryInterface(IPersistFile, PersistFile)) then
            try
              OleCheck(PersistFile.Load(PWideChar(AFileName), STGM_READ));
            finally
              PersistFile := nil;
            end
          else
            raise Exception.Create('Cannot initialize handler');

        OleCheck(ThumbnailProvider.GetThumbnail(ASize, Result, AAlpha));
      finally
        ThumbnailProvider := nil;
      end;
    finally
      ClassFactory := nil;
    end;
  finally
    FreeLibrary(DllModule);
  end;
end;