FMX: TScrollBar MouseDown and MouseUp events not triggering

  

I’ve created the following class to try to improve the response of a scroll bar. The reason is that if the code in the scrollbar’s onchange event is even slightly slow then updates don’t take effect until you stop dragging the thumb. This is annoying if redrawing a canvas in the onchange event for example. However, updating the canvas in a TTimer event is smooth. My guess is that this has something to do with the TScrollBar OnChange events being synchronous, whereas the TTimer events are asynchronous. My code attempts to solve the TScrollBar problem by triggering the event using a TTimer, which is enabled using the MouseDown event and disabled using the MouseUp event.
The issue is that the OnMouseDown event doesn’t trigger at all. I also tried just adding a TScrollBar component to the form at design time and then checking if its MouseDown or MouseUp events get triggered, but they don’t either. I managed to find a similar question from 2013, which was never answered.
https://codeverge.com/embarcadero.delphi.firemonkey/help-how-to-trap-mouse-down-mou/1057945
So is there a reason why these events are not triggered? How can I get them to trigger?
Also, if there’s another way to improve the response of a standard TScrollBar then please let me know? I’m using Delphi 10.4.
unit ScrollBarSmoothUnit;

interface

uses
System.Classes, System.UITypes, FMX.StdCtrls, FMX.Types;

type

TScrollBarSmooth = class(TScrollBar)
private
FTimer : TTimer;
FLastValue : Single;

procedure ScrollMouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Single);
procedure ScrollMouseUp(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Single);
procedure DoChange(Sender: TObject);
public
OnChangeSmooth : TNotifyEvent;

constructor Create(AOwner: TComponent); override;
end;

implementation

constructor TScrollBarSmooth.Create(AOwner: TComponent);
begin
inherited Create(AOwner);

AutoCapture := True;
HitTest := True;
OnMouseDown := ScrollMouseDown;
OnMouseUp := ScrollMouseUp;

FTimer := TTimer.Create(Self);
FTimer.Interval := 40;
FTimer.Enabled := False;
FTimer.OnTimer := DoChange;

FLastValue := -1;
end;

procedure TScrollBarSmooth.ScrollMouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Single);
begin
FTimer.Enabled := True;
end;

procedure TScrollBarSmooth.ScrollMouseUp(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Single);
begin
FTimer.Enabled := False;

DoChange(Self);
end;

procedure TScrollBarSmooth.DoChange(Sender: TObject);
begin
if Value = FLastValue then Exit; // No change
FLastValue := Value;

if Assigned(OnChangeSmooth) then OnChangeSmooth(Self);
end;

end.

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