how to force Draggable points to move along a line?

Hi All. I would like to use impoint to generate a draggable point. But I want to force it to move along a line. I try to do so by setPosition, but it does not work properly. Any help?

function test()

      h1 = impoint(gca,[5, 5])
      setString(h1,'h1');
      addNewPositionCallback(h1,@(h1) CallThis(1,[1 2],[ 2 ]));
      axis([0 10 0 10])

      function CallThis(varargin)

          pos = h1.getPosition()
          h1.setPosition([pos(1,1), 2*pos(1,1)])

      end

end

[Jan]

"It does not work properly" is a vague description only. Please do not let us guess, but explain the difference between your expectations and the results.

[Mohsen Davarynejad]

Sure, I mean that the point moves freely. It does not move along the line. Basically the setPosition command within the CallThis function does not update the position of the point.

Answer 1

[Roman Willi]

move along a line:

    obj.dragPoint = impoint();
    hp = addNewPositionCallback(obj.dragPoint,@(pos) point_move(obj,pos));

    function point_move(obj, pos)
        pos = [.....] % Calc Y Point of line
        axilim = [.....] % X axi limit
        fcn = makeConstrainToRectFcn('impoint',axilim, [pos pos]);
        setPositionConstraintFcn(obj.dragPoint, fcn);
    end