procedure TfrmMain.imgViewDrawBackBuffer(Sender: TObject);
type
  PRGBArr = ^TRGBArr;
  TRGBArr = array[0..32768] of TRGB;
const
  cMagenta: TRGB = (b: 255; g: 0;r: 255);
  cWhite: TRGB = (b: 255; g: 255;r: 255);
var
  rx, ry, rw, rh, sx, sy, sw, sh: Integer;
  y, x, i, j: Integer;
  SL: PRGBArr;
  Color: TRGB;
begin
  if chkSplit.Checked then begin
    imgView.GetRenderRectangles(rx, ry, rw, rh, sx, sy, sw, sh);

    // Position splitter in the middle of the view when activated
    if SplitPos = -1 then SplitPos:= (sw shr 1) + sx;

    x:= imgView.XBmp2Scr(SplitPos);  // Get splitter x position

    // Draw splitter
    if (x > 0) and (x < imgView.ClientWidth) then begin
      i:= 1;
      Color:= cMagenta;
      for y:= 0 to imgView.ClientHeight - 1 do begin
        SL:= imgView.BackBuffer.ScanLine[y];
        if y mod 4 = 0 then begin
          i:= -i;
          if i = -1 then Color:= cMagenta else Color:= cWhite;
        end;
        SL[x]:= Color;
      end;
    end;
  end;
end;