unit Unit1;

interface

uses
     Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
     Dialogs, StdCtrls, Math;

type
     Tvec2=record
      X,Y: single;
     end;

     TForm1 = class(TForm)
       Button1: TButton;
       procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X,
         Y: Integer);
       procedure FormCreate(Sender: TObject);
     private
       { Private declarations }
     public
       { Public declarations }
       function NormalizeVector(v: Tvec2): Tvec2;
       function cosVectors(a,b: Tvec2): Single;
     end;

var
     Form1: TForm1;
     vec2,vec22: Tvec2;

implementation

{$R *.dfm}

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
     Y: Integer);
begin
    vec2.X:=X-Button1.Left;
    vec2.Y:=Y-Button1.Top;
    vec2:=NormalizeVector(vec2);
    Button1.Caption:='ГГ Rotation='+FloatToStr(arccos(cosVectors(vec2,vec22))*180/pi);
end;

function TForm1.NormalizeVector(v: Tvec2): Tvec2;
var
     length: Single;
begin
     length:=sqrt(v.x*v.x + v.y*v.y);
     v.x:=v.x/length;
     v.y:=v.y/length;
     Result:=v;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
     vec22.X:=1;
     vec22.Y:=0;
end;

function TForm1.cosVectors(a, b: Tvec2): Single;
begin
     Result:=(a.x*b.x+a.y*b.y)/
              (Sqrt(a.x*a.x+a.y*a.y)*Sqrt(b.x*b.x+b.y*b.y));
end;

end.

struct Tvec2
{
   double X;
   double Y;
}

Tvec2 vec2,vec22=(1,0);
double rotation;

Tvec2 NotmalizeVector(Tvec2 v);
{
   double length=sqrt(v.x*v.x + v.y*v.y);
   v.x/=length;  
   v.y/=length;  
   Return(v);
}  

double cosVectors(Tvec2 a, b);  
begin  
      Return(
       (a.x*b.x+a.y*b.y)/  
      (Sqrt(a.x*a.x+a.y*a.y)*sqrt(b.x*b.x+b.y*b.y))
             );  
end;

Итератор или события{
   vec2.X=X-Pers.Left;  
   vec2.Y=Y-Pers.Top;  
   vec2=NormalizeVector(vec2);  
   rotation=arccos((cosVectors(vec2,vec22))*180/pi);
}