Animating the marquee

TTMSFNCWidgetMarqueeProgress is a circular progress ring built for indeterminate work — operations where you cannot report a real percentage, such as a server backup, a network request, or a long query. Instead of filling up to a known value, an arc segment rotates continuously around the ring to signal "something is happening". Reach for the marquee widget when you have no progress figure to show; use the determinate progress or gauge widgets when you do. This chapter covers starting and stopping the rotation, tuning its speed, and using Value to control the length of the moving arc.

Starting and stopping the rotation

Rotation is driven entirely by MarqueeAnimation, a TTMSFNCMarqueeAnimationOptions object on the widget. Set MarqueeAnimation.Active := True to start the sweep and False to stop it — for example, start it when a background task begins and stop it in the task's completion handler. The arc keeps its last position when stopped.

procedure TForm1.SetupMarquee;
begin
  FMarquee := TTMSFNCWidgetMarqueeProgress.Create(Self);
  FMarquee.Parent := Self;
  FMarquee.SetBounds(20, 20, 220, 220);

  // Value is the arc-segment length as a percentage (0..100) of the ring.
  // For an indeterminate "working" look, a partial arc that rotates reads best.
  FMarquee.Value := 30;
  FMarquee.CaptionOptions.Text := 'Server Chicago';

  // Drive the rotation. Interval is the millisecond delay between steps
  // (1..200, smaller is faster); Step is the degrees added per tick (1..20).
  FMarquee.MarqueeAnimation.Interval := 1;
  FMarquee.MarqueeAnimation.Step := 4;
  FMarquee.MarqueeAnimation.Active := True; // start rotating
end;

procedure TForm1.StopMarquee;
begin
  // Stop the rotation when the background task completes.
  FMarquee.MarqueeAnimation.Active := False;
  FMarquee.Value := 100; // fill the ring to signal "done"
end;

Speed: interval and step

Two properties shape how fast and how smoothly the arc travels:

• MarqueeAnimation.Interval — the delay in milliseconds between two animation steps. The valid range is 1 to 200, and the default is 1; a smaller value rotates faster. Values outside the range are ignored.
• MarqueeAnimation.Step — the angular increment in degrees added on each step. The valid range is 1 to 20, and the default is 4; a larger step makes the arc jump in bigger increments (faster but less smooth).

A low Interval with a small Step gives the smoothest rotation; raise Step for a faster, choppier sweep without changing the tick rate.

Arc length with Value

For this widget, Value is the length of the moving arc segment, expressed as a percentage (0..100) of the full ring — internally the sweep is Value / 100 * 360 degrees. A partial value such as 30 produces a comfortable rotating segment that reads clearly as "busy"; setting Value := 100 fills the whole ring, which is useful as a "finished" state once the work completes. StepIt raises Value by one and StepBy(AValue) adds a given amount, both clamping at 100 — handy if you want the segment to grow as a coarse, open-ended progress hint.

Pitfalls

• Nothing rotates until MarqueeAnimation.Active is True. Sizing and styling the ring alone draws a static arc; the sweep only runs while Active is set.
• Animation needs a solid fill. Rotation is only visible with a solid arc fill (CircleOptions.Fill.Kind := gfkSolid); the designer sets this up automatically, but set it explicitly when you build the widget in code (see Appearance).
• Value here is arc length, not real progress. It is a percentage of the ring, not a measured quantity. Leave it partial (for example 30) for the classic indeterminate look; set it to 100 only to show completion.
• Interval and Step silently clamp. Out-of-range assignments (for example Interval := 0 or Step := 50) are ignored, leaving the previous value.

See also

• Appearance — arc fill, track, thickness, border, and caption.
• API reference — full class reference.