How to make the Google loading spinner with TArc?

I'm considering to put a loading animation and a progress arc in a single object (like WhatsApp when loading a record), so I thought it was better to use TArc and TFloatAnimation, since I can control the StartAngle and EndAngle of the stroke. I'm trying to make the Google loading spinner logic but I'm very confused, it looks like there is a FloatAnimation with "linear" interpolation property that controls one of the angles and another one that looks to have a exponential or sinusoidal interpolation that start/end very fast and I can't see it, anyone had already tried to reproduce it? Thanks.

Image from web:

Requirement to make this:

• TArc
• TTimer

I find that you calling it a spinner is wrong. It's a spring in a harmonic motion plus a rotation effect.

This is the effect if you don't know it

You could read about it in Wikipedia (Warning it's written in French)

Now to solve this problem you need to define an array which will hold the values of the potential energy required to compress and stretch the spring.

PotentialEnergy: array[0..10] of Single;

The animation you are seeing is this

the spring stretching then getting compressed again. And in order to make it rotate we will define a rotation speed

RotationSpeed : Single;  

and the finale animation would look like this

This is final implementation of this animation:

var
  Form6: TForm6;
  Increment: Integer;
  PotentialEnergy: array[0..10] of Single;
  ReverseMotion : Boolean;
  RotationSpeed : Single;
implementation

{$R *.fmx}

procedure SetArray(var aData: array of Single; const aSource: array of Single);
var
  I: Integer;
begin
  for I := Low(aSource) to High(aSource) do
    begin
    aData[I] := aSource[I];
    end;
end;

procedure TForm6.Button1Click(Sender: TObject);
begin
  SetArray(PotentialEnergy, [5, 64, 48, 32, 24, 16, 14, 10, 8, 7]);
  Increment := -1;
  ReverseMotion := False;
  arc1.StartAngle := 0;
  arc1.EndAngle := 1;
  RotationSpeed := strtoint(edit1.text); // Degrees per 0.1 second
  timer1.Enabled := True;
end;

procedure TForm6.Timer1Timer(Sender: TObject);
begin
  if not ReverseMotion then
    begin
    Inc(Increment);
    arc1.EndAngle := arc1.EndAngle + PotentialEnergy[Increment];
    arc1.StartAngle := arc1.StartAngle + RotationSpeed;
    end
  else
    begin
    Inc(Increment);
    arc1.StartAngle := arc1.StartAngle + PotentialEnergy[Increment] + RotationSpeed;
    arc1.EndAngle := arc1.EndAngle - PotentialEnergy[Increment];
    end;

 if (Increment > 10)then
    begin
    ReverseMotion  := not ReverseMotion;
    Increment := -1;
    end;
end;

Also you could create animation like these

---

Update: after some synchronization(don't ask me how)

I found the could be exact replica of that google animation

Steps:

• set the timer to 30 ms.
• set the rotation speed to 5.
• set the height and width of the TArc to 102.
• set potential energy to this [23, 40, 39, 31, 23, 18, 15, 13, 11, 9, 7, 6, 5, 4, 4].

and the result is this (the google animation on the right)