README

RhoTrackBar

A modern, fully owner-drawn FireMonkey (FMX) trackbar / slider component for Delphi. TRhoTrackBar descends directly from TControl and paints its track, tick marks, value labels and thumb straight onto the canvas — no child controls are involved.

Registered on the component palette under the Rhody Controls category.

This code was developed using a combination of Human effort and AI assistance.

Features

• Horizontal or vertical orientation (Orientation); switching in the IDE automatically swaps width/height.
• Ten selectable thumb shapes via ThumbShape: circle, rectangle, rounded rectangle (pill), triangle, inverted triangle, diamond, pentagon, hexagon, star and an upward "pointer"/marker.
• Fully themeable thumb — fill colour, stroke colour, stroke thickness, corner radius, width and height.
• Tick marks and numeric labels with configurable frequency, colour, font size and an optional value suffix (e.g. "%", " dB").
• Live tracking toggle — fire OnChange continuously while dragging, or only once on release.
• Keyboard control — the thumb responds to the arrow keys (and Home/End), matching the built-in FMX trackbar, with a configurable step (Increment).
• Backward-compatible streaming — the enum ordering and custom DefineProperties entries keep older .fmx files loading correctly.

The trackbar can be made to work with styles by adusting the colors to match the style colors.

Installation

The component lives in a single unit, Source\uRhoTrackBar.pas, and ships with a design-time package.

1. Open Packages\RhoFMXTrackbarPackage.dpk in RAD Studio.
2. Build, then Install the package (right-click the package in the Project Manager → Install).
3. Add the Source folder to your project's or IDE's library/search path so uRhoTrackBar can be found.
4. TRhoTrackBar now appears on the Rhody Controls tab of the Tool Palette.

The package requires only the standard rtl and fmx runtime packages.

Build toolchain: RAD Studio (Delphi) with FireMonkey. Build from the command line by sourcing rsvars.bat and running msbuild on the .dproj.

Quick start

Drop a TRhoTrackBar onto an FMX form, or create one in code:

uses uRhoTrackBar;

var
  Bar: TRhoTrackBar;
begin
  Bar := TRhoTrackBar.Create(Self);
  Bar.Parent := Self;
  Bar.Min := 0;
  Bar.Max := 100;
  Bar.Value := 25;
  Bar.Orientation := TOrientation.Horizontal;
  Bar.ThumbShape := tsCircle;
  Bar.ValueSuffix := '%';
  Bar.OnChange := HandleChange;
end;

Reacting to changes:

procedure TfrmMain.HandleChange(Sender: TObject);
begin
  ProgressBar1.Value := (Sender as TRhoTrackBar).Value;
end;

See Demo\TrackBarDemoProject.dpr for a full sample form driving a progress bar and a colour-interpolated rectangle from several trackbars.

Properties

Value / range

Ticks & labels

Track & thumb appearance

TThumbShape values:

tsCircle, tsRectangle, tsRoundRect, tsTriangle, tsInvertedTriangle,
tsDiamond, tsPentagon, tsHexagon, tsStar, tsPointer

Note: tsRectangle honours ThumbCornerRadius (0 gives sharp corners), while tsRoundRect is always a rounded "pill" independent of the radius.

Standard inherited FMX properties are also published (Align, Anchors, Position, Size, Margins, Padding, Opacity, Visible, Enabled, RotationAngle, Hint, Cursor, etc.).

Events

Standard FMX mouse, drag and paint events (OnMouseDown, OnMouseMove, OnMouseUp, OnMouseWheel, OnClick, OnPaint, OnResize, …) are published as well.

Keyboard

The control is focusable (TabStop is enabled), so it can be reached with Tab or by clicking on it. Once focused, it responds to the arrow keys just like the built-in FMX trackbar. Each press changes Value by Increment (default 1) and fires OnChange.

Set Increment to tune the step — e.g. 0.1 for a fine 0..1 slider, or a larger value for coarse jumps. LiveTracking only affects mouse dragging; arrow keys always fire OnChange on each press.

How it works

• Paint draws the track, then tick marks (if ShowTicks), then the thumb on top — everything on this control's own canvas.
• Resize recomputes the track rectangle and re-centres the thumb; the track ends are inset by half the thumb so it never overhangs at Min/Max.
• Thumb geometry is rebuilt each paint as a TPathData in absolute control coordinates, snapped to the device-pixel grid for crisp edges under scaling.
• Mouse handling captures the pointer on MouseDown (also taking keyboard focus), maps coordinates to a value in CalculateValueFromCoords, and releases capture on MouseUp.
• Keyboard handling overrides KeyDown; handled keys are swallowed so they don't bubble up to a parent (e.g. scrolling) or move focus off the control.

Project layout

Source\      uRhoTrackBar.pas        the component (single unit)
Packages\    RhoFMXTrackbarPackage   design-time package (.dpk/.dproj)
Demo\        TrackBarDemoProject     sample FMX application

License

MIT