Проверить, находится ли курсор на линии

Code:

{

Check if a Point(X,Y) (e.g a Cursor) is on a Linie (x1,y1) ; (x2,y2)

d = line width (min. 1)

}

function CursorOnLinie(X, Y, x1, y1, x2, y2, d: Integer): Boolean;

var

  sine, cosinus: Double;

  dx, dy, len: Integer;

begin

  if d = 0 then d := 1;

  asm

    fild(y2)

    fisub(y1) // Y-Difference

   fild(x2)

    fisub(x1) // X-Difference

   fpatan    // Angle of the line in st(0)

   fsincos   // Cosinus in st(0), Sinus in st(1)

   fstp cosinus

    fstp sine

  end;

  dx  := Round(cosinus * (x - x1) + sine * (y - y1));

  dy  := Round(cosinus * (y - y1) - sine * (x - x1));

  len := Round(cosinus * (x2 - x1) + sine * (y2 - y1)); // length of line

if (dy > -d) and (dy < d) and (dx > -d) and (dx < len + d) then Result := True

  else

     Result := False;

end;

procedure TForm1.FormPaint(Sender: TObject);

begin

  Canvas.Pen.Width := 1;

  Canvas.MoveTo(0, 0);

  Canvas.LineTo(Width, Weight);

end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,

  Y: Integer);

var

  p: TPoint;

begin

  GetCursorPos(p);

  p := ScreenToClient(p);

  if CursorOnLinie(p.x, p.y, 0, 0, Width, Height, 1) then

    Caption := 'Mouse on line.'

  else

    Caption := 'Mouse not on line.'

end;