dragging out an object from mouse click?

hey all, im trying to create a script that enables an arrow to be spawn when the user holds down a mouse button and then disapear when the mouse is released. easy enough right?

now this i can do no problem but im struggling to get the effect i want which is the arrow to grow and be dragged out as the user moves the mouse while the button is down.

ive made a small image to help show what im after http://i.imgur.com/2UXRl22.png

point A is mouse down point B is mouse up

ive tried a few ways to get this working but none of which work correctly with a orpographic camera . the arrow grows in size from 0 to the distance from point a to point b

any help would be great

Poll the screen space position of the mouse on getMouseButtonDown() and then in update if (Input.getMouseButton()). Use Vector2.Distance to get a float that you can then use to scale the object as you desire. That’s how I would do something like this. You can also at the end of update get a “deltaDistance” for how far the mouse has moved which will give you even more granular control. To do this just save the last position from and update and subtract it from the current position to get the delta.