Animating anchor points in Flash CS5 - Shape goes mad!

Question

I'm having problems creating a very simple shape animation in Flash CS5.

I have 20 frames, 3 keyframes (at 1, 10 and 20).

The following screenshots are from Flash, with onion skin turned on for all 20 frames. (Had to pud link to the images since I can't embed them)

When I move a single anchor point, sometimes it's OK, like this:

But if I move the point a little futher, the whole shape morphs into something I never created, like this:

In both cases, I only moved the same single anchor point - the point of the upper spike.

Is there a way of telling Flash that I only want the movement I made and no random morphing ?

Answer 1

It really messes with your mind, doesn't it? Fortunately, it's not hard to understand and it's not hard to fix.

When you Shape Tween (Flash-speak for morphing), the Flash authoring environment does some very fancy mathematical calculations on the geometry of the shape to try to figure out the shortest "distance" from Point(s) A to Point(s) B. If the change is not too great, and/or the shape is simple, you get what you expect. If it's a big change, or a complex shape, things can look pretty weird.

The answer is to use Shape Hinting (Modify > Shape > Add Shape Hint). Rather than get into a detailed explanation, here's the Flash Help Page, and here's a good tutorial by Todd Perkins. He begins, appropriately enough, with the words: "Creating a Shape Tween can be a challenging process..."

Good luck!

Answer 2

I found the same problem while creating an animation. It's a but that appears while creating the shape tweening animation (curved object). The starting keyframe is ok, but when you insert the ending keyframe the software increases the number of anchor points, and the animation goes mad.