unit Circle;

interface

uses Windows;

type

TCircle = class
private
 SqrR: Integer;
 Bounds: TRect;
public
 // не будет усложнять все свойствами
 X0: Integer;
 Y0: Integer;
 R: Integer;

 constructor Create(AX, AY, AR: Integer);
 function PointInCircle1(AX, AY: Integer): Boolean;
 function PointInCircle2(AX, AY: Integer): Boolean;
end;

implementation

uses Types;

constructor TCircle.Create(AX, AY, AR: Integer);
var
 r2: Integer;
begin
 X0:=AX;
 Y0:=AY;
 R:= AR;
 SqrR := R * R;
 r2 := Trunc(R/2) + 1;
 Bounds.Left := X0 - r2;
 Bounds.Right := X0 + r2;
 Bounds.Top := Y0 - r2;
 Bounds.Bottom := Y0 + r2;
end;

// вычисляем напрямик
function TCircle.PointInCircle1(AX, AY: Integer): Boolean;
begin
 Result := Sqr(AX-X0)+Sqr(AY-Y0) <= SqrR;
end;

function TCircle.PointInCircle2(AX, AY: Integer): Boolean;
begin
 if ((Bounds.Left <= AX) and (AX <= Bounds.Right) and
     (Bounds.Top <= AY) and (AY <= Bounds.Bottom)) then
    // можно попробовать и так и так
    Result := Sqr(AX-X0)+Sqr(AY-Y0) <= SqrR //PointInCircle1(AX, AY)
 else
   Result := false;
end;

end.

TCircle=Class(Telement)
     pnt:Tpoint;
     image:TImage;
     index:word;
     R:TRect;
     Procedure Draw;
     Constructor Create(pnt0:Tpoint;image0:TImage;index0:word);
     Destructor Destroy;
     Function Select(move_point0:Tpoint):boolean;
     Procedure Allocation;
    end;