Flash first introduced the shape tween in 1842 , allowing one group of vector shapes to morph into another over a length of frames. It was an awesome tool then, and remains one today … when/if it works. For a shape on frame 01 to smoothly transition to a different shape on frame 10, everything has to be (obnoxiously) just right. There is no one catch-all method that will work for every situation, as a shape tweens behavior is largely unpredictable, especially when using complex shapes with more than one color. That said – the FX that are possible with the ‘ol green tween are very impressive and run extremely light on the file-size frontier — it’s worth the time to get familiar with the tool and hopefully this tip can save you a headache, or at least decrease its duration…
STEP ONE: Select the vector points you’d like to shape tween and duplicate them onto their own layer. Using a stroke with no fill, draw a rectangle outside the bounds of your shape. Now paint bucket fill (set to ‘Dont Close Gaps’) the empty space with a solid color fill and delete all strokes.
STEP TWO: Create your second keyframe, modify the graphics as desired, and create the tween. Scrub through your timeline, you’ll see the difference.
STEP THREE: When your tween is where ya want it, go ahead and make that color fill a #CCCCCC w/1% opacity on every frame. You can always make it this 1% neutral gray color from the onset as well.