İki nokta arasındaki açı kaç derece?

function RelativeAngle(X1,Y1, X2,Y2 : Integer) : Integer;
 
var
 
  Theta : Extended;
 
  XDist,
 
  YDist : Integer;
 
begin
 
  Result := 0;
 
 
 
  //arctan((y2-y1)/(x2-x1))
 
  XDist := X2 - X1;
 
  YDist := Y1 - Y2;
 
  if (XDist = 0) and (YDist=0) then exit;
 
 
 
  if YDist=0 then
 
    Theta := arctan((X2-X1))
 
  else
 
    Theta := arctan((X2-X1)/(Y1-Y2));
 
 
 
  Result := Round(RadToDeg(Theta));
 
  if (X2 >= X1) and (Y2 >= Y1) then //Quadrant = 2
 
    Result := 90+(90-Abs(Result))
 
  else
 
  if (X2 <= X1) and (Y2 >= Y1) then //Quadrant = 3
 
    Result := 180 + Result
 
  else
 
  if (X2 <= X1) and (Y2 <= Y1) then //Quadrant = 4
 
    Result := 270+90-Abs(Result);
 
end;