Magnifying glass for the keyboard cursor

Question

I would like to create a magnifying glass to enlarge the region around where the keyboard cursor is positioned and also the focus on a form. I wonder if anyone has any suggestions on the subject.

I found a source but it’s about the mouse position.

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;

end.

Answer 1

To capture the Rect wrapped around the object with focus use the function:

GetWindowRect(GetFocus, Srect);

If you replace in your code the part:

Srect:=Rect(Kursor.x,Kursor.y,Kursor.x,Kursor.y);

by the above function, will already produce an effect close to the desired one, being necessary to apply only a basic mathematics, changing the value of the top, left, right and bottom of Srect so that a greater coverage is applied to zoom.

For this, subtract an Offset from Left and Top, and increment an Offset in Right and Bottom