How to reverse Delphi's TTrackbar.Orientation values?

Question

When a TTrackbar.Orientation property is set to trVertical, the Min value is on top and the Max is on the bottom:

How can I invert the Min/Max positions? If I would like to use a TrackBar in vertical orientation for a Volume control for audio output, for instance, I would need the Min on the bottom and the Max on the top.

Answer 1

There is no built in way to do that. But you could reverse the min-max value by code:

volume := (trackbar.Max - trackBar.Position) + trackBar.Min;

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Regarding the presentation of the ToolTip value, @Victoria kindly provides a solution that intercepts the TTN_NEEDTEXT windows message, and corrects the text output:

uses
  Winapi.CommCtrl;

type
  TTrackBar = class(Vcl.ComCtrls.TTrackBar)
  private
    procedure WMNotify(var Msg: TWMNotify); message WM_NOTIFY;
  end;

implementation

procedure TTrackBar.WMNotify(var Msg: TWMNotify);
begin
  if Msg.NMHdr.code = TTN_NEEDTEXTW then
  begin
    PToolTipTextW(Msg.NMHdr)^.hInst := 0;
    PToolTipTextW(Msg.NMHdr)^.lpszText := 
      PChar('Position: ' + IntToStr((Max - Position) + Min));
  end
  else
    inherited;
end;