delphi – 如何在将屏幕对象处理到DrawFocusRect时消除屏幕闪烁

我试图在我多年前开发的Apprehend Screen Capture Component中围绕选定的屏幕对象绘制一个聚焦矩形.我可以通过Handles：= WindowFromPoint(P)获取光标下对象的句柄来绘制DrawFocusRect;但这要求我隐藏然后显示自己的工作,否则返回自我的句柄.

不幸的是,当我隐藏并显示表单时,它会在隐藏和显示表单时导致闪烁.

我可以毫无问题地获得所选对象的位图,只是绘制选定的对象让我疯狂.

有没有人有任何建议围绕选定的对象绘制一个FocusedRect,所以没有闪烁？如果表单位于屏幕顶部,是否有任何API可以获取屏幕句柄？

我尝试使用Handles：= WindowFromDC(ScreenDC),所以我不必隐藏和显示表单,但WindowFromDC仍然返回表单而不是屏幕.

TCaptureObjectForm是透明的,位于屏幕上方.我需要组件中的TCaptureObjectForm.

// FormMouseMove事件 – 已添加08/2/2011

procedure TCaptureObjectForm.FormMouseMove( Sender: TObject; Shift: TShiftState; X, Y: Integer );
const
  crHand = -18;
var
  P: TPoint;
  Handles: HWND;
  Rect: TRect;
  ScreenDC: HDC;
begin
  // hide the TCaptureObjectForm form so the screen is found by WindowFromPoint
  Self.Hide;
  // get the object on the screen
  GetCursorPos( P );
  Handles := WindowFromPoint( P );
  // tried this but it returns self.handle rather than the screen handle
  //ScreenDC := GetDC( 0 );
  //Handles := WindowFromDC(ScreenDC);
  //ReleaseDC( 0, ScreenDC );
  // restore the TCaptureObjectForm
  Self.Show;
  // get object rect
  GetWindowRect( Handles, Rect );
  // draw a rect to show it is focused
  Self.Canvas.DrawFocusRect( Rect );
end;

This article是Microsoft的Visual Basic中的一个示例,它执行与您所需的非常相似的操作.

他们采取以下方法：

>在Form_MouseDown中捕获鼠标.
>当鼠标移动时,在用鼠标指向的窗口周围绘制一个矩形：Form_MouseMove.
>在Form_MouseUp中释放鼠标,并使整个屏幕无效以删除最后绘制的矩形.

他们直接在他们选择的窗口中绘制.我不认为使用透明窗口方法可以避免所有闪烁.

该代码示例似乎不完整且效果不佳,因此我对其进行了修改(并转换为Delphi)：

// Not global variables, but private form ones
var
  HwndLastTracked: HWND;
  CapturedMouse: boolean;

procedure InvertTracker(hwndWindow: HWND);
var
  rc: TRect;
  dc: HDC;
  pen, oldPen: HPEN;
  oldBrush: HBRUSH;
  style, exStyle: longint;
  cx, cy: integer;
begin
  GetWindowRect(hwndWindow, rc);

  // Window coordinates of the origin (top-left corner) of a window is (0, 0)
  OffsetRect(rc, -rc.Left, -rc.Top);

  // DC returned by GetWindowDC covers the full window area, but in Windows
  // Vista/7 it seems to be clipped excluding the nonclient region, due to
  // DWM handling nonclient drawing, so it doesn't allow painting over it.
  // Thus we need to skip this nonclient area and that is why I adjust the
  // window rect to match the client area. Using GetClientRect instead of
  // GetWindowRect is not suitable as excludes scroll bars and child 
  // parts drawed in WM_NCPAINT, such as Windows' WS_EXEDGEs and Delphi's
  // bevels.

  style := GetWindowLong(hwndWindow, GWL_STYLE);
  exStyle := GetWindowLong(hwndWindow, GWL_EXSTYLE);

  if style and WS_CAPTION <> 0 then begin
    if exStyle and WS_EX_TOOLWINDOW <> 0 then
      cy := GetSystemMetrics(SM_CYSMCAPTION)
    else
      cy := GetSystemMetrics(SM_CYCAPTION);

    // discard area covered by caption 
    Inc(rc.Top, cy);
  end;

  if style and WS_THICKFRAME <> 0 then begin
    cx := GetSystemMetrics(SM_CXFRAME);
    cy := GetSystemMetrics(SM_CYFRAME);
  end
  else if style and WS_DLGFRAME <> 0 then begin
    cx := GetSystemMetrics(SM_CXDLGFRAME);
    cy := GetSystemMetrics(SM_CYDLGFRAME);
  end
  else if style and WS_BORDER <> 0 then begin
    cx := GetSystemMetrics(SM_CXBORDER);
    cy := GetSystemMetrics(SM_CYBORDER);
  end
  else begin
    cx := 0;
    cy := 0;
  end;

  if (cx <> 0) or (cy <> 0) then begin
    // discard area covered by borders
    OffsetRect(rc, cx, cy);
    Dec(rc.Right, cx*2);
    Dec(rc.Bottom, cy*2);
  end;

  // Windows API functions don't raise exceptions, so I don't use try-finally

  dc := GetWindowDC(hwndWindow);

  // Option 1: focused rect
  //DrawFocusRect(dc, rc);

  // Option 2: inverted thick border
  SetROP2(dc, R2_NOT);
  pen := CreatePen(PS_INSIDEFRAME, 3 * GetSystemMetrics(SM_CXBORDER), 0);
  oldPen := SelectObject(dc, pen);
  oldBrush := SelectObject(dc, GetStockObject(NULL_BRUSH));

  Rectangle(dc, rc.Left, rc.Top, rc.Right, rc.Bottom);

  SelectObject(dc, oldBrush);
  SelectObject(dc, oldPen);
  DeleteObject(pen);
  // End option 2

  ReleaseDC(hwndWindow, dc);
end;

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if SetCapture(Handle) <> 0 then begin
    CapturedMouse := true;
    HwndLastTracked := 0;
    Screen.Cursor := crCross;
  end;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState;
  X, Y: Integer);
var
  hwndCaptured: HWND;
begin
  if CapturedMouse then begin
    hwndCaptured := WindowFromPoint(ClientToScreen(Point(X, Y)));

    // Uncomment this for track root windows instead of childs
    //hwndCaptured := GetAncestor(hwndCaptured, GA_ROOT);

    if hwndCaptured <> HwndLastTracked then begin
      if HwndLastTracked <> 0 then
        InvertTracker(HwndLastTracked);
      InvertTracker(hwndCaptured);
      HwndLastTracked := hwndCaptured;
    end;
  end;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if CapturedMouse then begin
    ReleaseCapture;
    CapturedMouse := false;

    if HwndLastTracked <> 0 then begin
      InvertTracker(HwndLastTracked);
      HwndLastTracked := 0;
    end;

    Screen.Cursor := crDefault;
  end;
end;

以下是Microsoft在Visual Studio的Spy中如何使用此技术的屏幕截图.红色的气球和文字都是我的！