David Stiller’s blog

There are two ways to apply a motion tween in Flash.  Once you select the span of frames between two keyframes, either a) choose “Motion” from the Tween listbox in the Property inspector or b) use the Create Motion Tween mechanism.  The latter is available under Insert > Timeline > Create Motion Tween or by right-clicking (Win) / Command+clicking (Mac) and choosing Create Motion Tween from the context menu.  At first glance, these approaches simply look like two ways to accomplish the same thing, but there’s actually a big difference between them. 

Shapes

As a rule, motion tweens cannot be applied to shapes.  Shapes are controlled by shape tweens and must first be converted into symbols before a motion tween is possible.  If you try to apply a motion tween to the span of frames between two shape keyframes, you’ll either get a “broken tween,” as indicated by a dashed line in the span of frames, or Flash will create two new symbols for you and tween those instead.  This is the difference between using the Property inspector or Create Motion Tween to achieve your results (at least, as of this writing [Flash 8]).

The Property inspector’s tween simply fails, as it should — remember, motion tweens cannot be applied to shapes.  The Create Motion Tween mechanism attempts to help you out by creating the necessary symbols for you, but this “helpfulness” can lead to frustration when used in anything but the simplest of movies.

The auto-generated symbols go by the names Tween 1 and Tween 2, which aren’t specially descriptive labels.  If you’ve done this more than once in a given FLA, the new symbols will be named Tween 3 and Tween 4, and so on, with numbers going as high as needed.  Enough of these will clutter up your Library, especially because the names aren’t meaningful.  If you delete these symbols — and beginners often do — the tweens they facilitate simply vanish.

Much better to go with the appropriate tween type:  shape tweens for shapes, motion tweens for symbols.

Shape Objects (the Object Drawing Model)

Flash 8 introduced a new type of graphic element, the shape object.  This is something like a grouped shape (Modify > Group) and mysteriously hovers between the realms of shape and symbol.  This feature provides a new paradigm for how to draw in Flash; details are available in the Help docs, specifically the Using Flash book, under “About Flash drawing models” (definitely interesting reading).  This feature can be toggled in the Tools panel when a shape tool, such as the Oval Tool or Rectangle Tool, is chosen.

Shape objects can be motion tweened, as if they were symbols.  Interestingly enough, they can also be shape tweened.  If you choose to apply a motion tween to shape object keyframes, make sure to use the Property inspector.  As with shapes, the Create Motion Tween mechanism will create symbols in the Library — and in this case, they simply aren’t necessary.

Symbols

By this point, you’re already aware that symbol keyframes are the primary candidate for motion tweens.  In this case, the Create Motion Tween mechanism leaves well enough alone:  no extra symbols are created, and none are needed, in the application of the motion tween.  That said, even here, there’s a difference between Create Motion Tween and the Property inspector.

If you apply a motion between to symbol keyframes with the Property inspector, you’ll see that the Scale checkbox is selected by default, which means that scaling may be tweened in addition to other properties, such as position.  Other checkboxes are left unselected.  If you do the same by way of the Create Motion Tween mechanism, you’ll find that the Sync and Snap checkboxes are also selected.  For details on these parameters, read the “Tweening instances, groups, and type” entry in Using Flash.

This entry was posted on Saturday, December 16th, 2006 at 5:53 pm and is filed under Flash. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.