Mouse magnification on Form

Mit diesem Beispiel kann der Desktop-Bildschirm auf die Form gezoomt werden. Dabei wird der Bereich um die Maus vergrößert und auf die Form projiziert.

Es wird benötigt : 1xTrackBar, 1xImage, 1xCheckBox, 1xTimer

private
     procedure WMGetMinMaxInfo(var Msg: TWMGetMinMaxInfo); message WM_GETMINMAXINFO;
     
//

procedure TForm1.WMGetMinMaxInfo(var Msg: TWMGetMinMaxInfo);
begin
   inherited;
   Msg.MinMaxInfo^.ptMinTrackSize := Point(158, 177); // min form size
   Msg.MinMaxInfo^.ptMaxTrackSize := Point(350, 350); // max form size (width, height)
end;


procedure TForm1.FormResize(Sender: TObject);
begin
		// panel in the middle of the form
  Panel1.Left:=(Form1.ClientWidth Div 2) - Panel1.Width div 2;
  Panel1.Top:=(Form1.ClientHeight Div 2) - Panel1.Height div 2;
  Image1.Picture:=nil;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
	Timer1.Interval:=0;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
var
  Srect,Drect,PosForme:TRect;
  iWidth,iHeight,DmX,DmY:Integer;
  iTmpX,iTmpY:Real;
  C:TCanvas;
  hDesktop: Hwnd;
  Kursor:TPoint;
begin
 If not IsIconic(Application.Handle) then begin
  hDesktop:= GetDesktopWindow;
  GetCursorPos(Kursor);
 	PosForme:=Rect(Form1.Left,Form1.Top,Form1.Left+Form1.Width,Form1.Top+Form1.Height);
  If not PtInRect(PosForme,Kursor) then begin

    If Panel1.Visible=True then Panel1.Visible:=False;
    If Image1.Visible=False then Image1.Visible:=True;

 	 iWidth:=Image1.Width;
		 iHeight:=Image1.Height;
    Drect:=Rect(0,0,iWidth,iHeight);

    iTmpX:=iWidth / (Slider.Position * 4);
    iTmpY:=iHeight / (Slider.Position * 4);

    Srect:=Rect(Kursor.x,Kursor.y,Kursor.x,Kursor.y);
    InflateRect(Srect,Round(iTmpX),Round(iTmpY));
    // move Srect if outside visible area of the screen
    If Srect.Left<0 then OffsetRect(Srect,-Srect.Left,0);
    If Srect.Top<0 then OffsetRect(Srect,0,-Srect.Top);
    If Srect.Right>Screen.Width then OffsetRect(Srect,-(Srect.Right-Screen.Width),0);
    If Srect.Bottom>Screen.Height then OffsetRect(Srect,0,-(Srect.Bottom-Screen.Height));

   C:=TCanvas.Create;
   try
     C.Handle:=GetDC(GetDesktopWindow);
     Image1.Canvas.CopyRect(Drect,C,Srect);
    finally
      ReleaseDC(hDesktop, C.Handle);
      C.Free;
    end;
    If cbSrediste.Checked=True then begin         // show crosshair
    	with Image1.Canvas do begin
        DmX:=Slider.Position * 2 * (Kursor.X-Srect.Left);
        DmY:=Slider.Position * 2 * (Kursor.Y-Srect.Top);  
   		 MoveTo(DmX - (iWidth div 4),DmY);          // -
   		 LineTo(DmX + (iWidth div 4),DmY);          // -
    		 MoveTo(DmX,DmY - (iHeight div 4));
   		 LineTo(DmX,DmY + (iHeight div 4));
      end;                                         // with image1.Canvas
    end;                                           // show crosshair
  	Application.ProcessMessages;
	end                                              // Cursor not inside form
   else begin                                      // cursor inside form
   	If Panel1.Visible=False then Panel1.Visible:=True;
   	If Image1.Visible=True then Image1.Visible:=False;
  end;
 end;                                              // IsIconic
end;