How to adjust a TrackBar thumb size?

Question

I can't adjust a TTrackBar thumb size to a higher size. See the image:

I got a small thumb on the left, and I can't make it bigger (but not the TrackBar itself).
Desired thumb size is shown on an image with a red area.
Maybe I can use WINAPI somehow? C++ apps have bigger thumb often.

This is what I'm actually hopping for:

Answer 1

It would seem like this cannot be done with the standard trackbar control. Indeed, I cannot see any trackbar style or trackbar message related to this. There is only the TBM_SETTHUMBLENGTH, which you also can access from VCL's TTrackBar.ThumbLength, but this also affects the height of the background sunken rectangle.

A corollory is that I doubt the observation that "C++ apps have bigger thumb often".

Of course, you can always make your own trackbar-like control.

Or do you only want to shrink the sunken rectangle? Then just set ShowSelRange to False in the Object Inspector. But if themes are on, you still cannot make the thumb bigger than about 24.

If you are on an old version of Delphi with no TrackBar.ShowSelRange, you need to remove the window style TBS_ENABLESELRANGE manually. You can do this at any time using SetWindowLong, or you can do it in CreateParams of a subclassed trackbar control. The simplest way might be to use an 'interposer class':

type
  TTrackBar = class(ComCtrls.TTrackBar)
  protected
    procedure CreateParams(var Params: TCreateParams); override;
  end;

...   
implementation

{ TTrackBar }

procedure TTrackBar.CreateParams(var Params: TCreateParams);
begin
  inherited;
  Params.Style := Params.Style and not TBS_ENABLESELRANGE;
end;

To get the appearance in the Notepad++ screenshot, you should also set TickMarks to tmBoth and TickStyle to tsNone.

This doesn't answer your question, though, which was about making the thumb larger. This will make the sunken rectangle smaller... From your screenshots, however, I would guess this is what you want.

Answer 2

Trackbar is one of the native controls that support custom draw. Basically, when themes are enabled, you can control various aspects of drawing the control, or you can tell the OS that you're overtaking drawing parts yourself. See more about custom draw here.

We don't have to overtake any drawing to play with the sizes of some parts a little bit. It is the VCL that draws the channel (the recessed tracking background), and the ticks. For ticks, there are already properties we can use. For the channel, we can deflate the rectangle a bit, and the VCL will take over from there. The thumb is drawn by the default window procedure, but it doesn't matter, the OS will draw the thumb to the modified rectangle.

The below example (for a horizontal trackbar) intercepts WM_NOTIFY notification sent to the form to carry out these modifications. This will only work if the trackbar is placed directly on the form. If this is not the case, you can derive a new control that descends from TTrackBar to handle CN_NOTIFY, or subclass the control, or its parent for WM_NOTIFY. All that matters is to handle the notification before the actual drawing is performed.

This is how the example looks:

type
  TForm1 = class(TForm)
    Button1: TButton;
    TrackBar1: TTrackBar;
    procedure FormCreate(Sender: TObject);
  protected
    procedure WMNotify(var Msg: TWMNotify); message WM_NOTIFY;
  end;

...

uses
  themes, commctrl, xpman;

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  if ThemeServices.ThemesEnabled and
      (TrackBar1.Orientation = trHorizontal) then begin
    TrackBar1.TickMarks := tmBoth;
    TrackBar1.TickStyle := tsNone;
    TrackBar1.ThumbLength := 38;
  end;
end;

procedure TForm1.WMNotify(var Msg: TWMNotify);
begin
  if ThemeServices.ThemesEnabled and
      (TrackBar1.Orientation = trHorizontal) then begin

    if (Msg.IDCtrl = Longint(TrackBar1.Handle)) and
        (Msg.NMHdr.code = NM_CUSTOMDRAW) and
        (PNMCustomDraw(Msg.NMHdr).dwDrawStage = CDDS_ITEMPREPAINT) then begin

      case PNMCustomDraw(Msg.NMHdr).dwItemSpec of
        TBCD_THUMB: InflateRect(PNMCustomDraw(Msg.NMHdr).rc, -4, 0);
        TBCD_CHANNEL:
          with PNMCustomDraw(Msg.NMHdr).rc do begin
            Top := Bottom div 2 + 2;
            Bottom := Top + 5;
            Inc(Left, 4);
            Dec(Right, 4);
          end;
      end;
    end;
  end;

  inherited;
end;