Hard Cider: And Never The Tween
Will Meet - Troubleshooting The Flash Tween Function
The Trouble with
Tweens
By
Jeff Peterson
Level - Intermediate [assuming some familiarity with
basic Flash features]
"It's the little foxes, that spoil the vines:
for our vines have tender grapes." Song of Solomon
2:15
One of the joys of working with Flash is
the Tween function. It can also be one of the most
aggravating, annoying, and frustrating ventures when things
don't go as planned. Over the course of a year, I've spent
many hours working against a deadline, pulling out my
hair as a simple task turns into a nightmare. All I
want to do is move one object across a stage - usually
a simple Tween - only to see my objects refusing to budge
or flying off in nutty directions! This article will
highlight two frustrating problems and fixes for the oddities
of Tweens.
First, some background.What
is the Tween function? Tweening is the ability to
create a beginning object in one frame of a movie sequence
and another object in an ending frame and then allow the
computer to generate every intermediate object. This auto-animating
function saves hours of design time. Basically there are
two types of Tweens: Shape and Symbol. The first
type of Tween, a Shape Tween, is a type of morphing.
You take a star in one frame and end with a circle in
the last frame. Flash will generate all the frame shapes
in between [hence: Tweening]. So you might see the star
change first to a square then to the circle over 10 movie
frames. The second type of Tween, called a Symbol Tween,
takes a single object, converted to a symbol [keyboard
- F8], and moves, rotates, and/or scales this
symbol over several frames of the Flash movie. [For
more information on Tweens and their functions, see the
help guide that came with Flash.]
Figure A
What are the Troubles
with Tweens?
For the sake of brevity, I will list the
problem, causes, followed by solutions. Each of these
problems, when I first encountered them, took me over
a half a day to solve. They are the kind of problems
that just shouldn't happen. Some of them are bugs. Others
are easy mistakes.
Trouble 1:Text
symbols do not scale or fade. You create a word or
sentence and turn it into a symbol [F8]
as usual. You try to use it in a sequence. It plays just
as it should in the timeline and work area, but once published,
the symbol may move but it will not scale or fade.
Figure B
Cause: You are using system fonts
[_serif, _sans, _courier], or Postscript fonts [Flash
4 does not handle Postscript fonts well]. Macromedia recommends
device or system fonts to save space or to use in text
fields to guarantee good display, but for some reason
the use of system fonts causes the Tween functions not
to work properly. While PS fonts may work, often there
are shape oddities like the letter Q filled in with a
solid color, or Flash itself will crash using PS fonts.
Solution: Change the font in your
symbol to any True Type font.
Solving this problem took me over a day. It was maddening
because it shouldn't have been a problem. That's what
makes it hard to figure out.
Trouble 2: Symbols don't
move in the direction you expect. You use a motion
guide to move a symbol or symbols across the screen over
several frames, but rather than following the expected
path, the symbol moves in a different direction or snaps
to the middle.
Figure C
Causes:
a) Your symbol is not snapped to the motion guide
line;
b) You have two or more symbols on the same layer
of the movie;
c) You have a shape, not a symbol on the layer with
the symbol;
d) You have two ore more layers being governed by
a single motion guide
This type of problem happens often. You
have to look at four possible causes to find the proper
solution. A Motion Guide Layer uses something like a line
or zigzag to direct the action of a symbol across the
stage or screen. The Guide Layer is colored blue or purple
in the Timeline and the Symbol Layer underneath it is
indented to show that is governed by the layer above
(see below- Figure E).
Solution a) and b): The most
common reason that a symbol does not move as expected
is that the symbol is not snapped to the guide line
at the beginning and the end of the guide. First, make
sure the Symbol Layer is unlocked. Under the View Menu,
choose Snap, then in the first frame of the sequence,
select the symbol. When you do, cross hairs should be
revealed. The cross hairs show the center point of the
symbol. If you do not see the symbol outlined and having
a cross hair, then you do not have a symbol in the first
place, you have a shape object and that is your problem!
If you do see cross hairs, grab the symbol by the cross
hairs and drag it to the guideline. When the cross hairs
are over the guideline, the "+" will change to an "o".
Now when you let go, it will snap to the line. Make
sure the last frame of the Tween is also snapped to
the line. That should solve your problem.
Figure D
Solution c): If you have more than
one symbol or object on a layer and create a Tween,
Flash will automatically turns all objects on a single
layer into ONE symbol. This benefit of Flash can also
make it difficult to figure out what's gone wrong. Sometimes,
when editing frames, I find I have unknowingly added
2 or more objects on the same timeline layer. I might
place an object like a square in a frame 7 and
hit F6 to create a duplicate frame in
frame 29. Later I change the square in frame
7 into a Symbol [F8]. Then I create the
Tween between 7 and 29. But guess what! Although it
looks like I have the same square in both 7 and
29, Flash will turn the square in frame 29 [which
is not yet a symbol] to a new symbol. Suddenly, I have
2 symbols on the same layer, and neither one will follow
the guideline!
What to look for: Go to Window
> Library and open your library. Look for Symbols
named Tween 1, Tween 2, etc. If you see anything
like that, you will find that you have created a new
set of symbols and the resulting behavior can be very
odd. The symbols will jump around the stage or move
in opposite directions.
Figure E
To solve the problem, you must delete all the
Tween Symbols from the layer and start fresh. Place
your original symbol [square] in frame 7. Now
duplicate the frame in 29 [F6]. Then create
the motion, scale, and/or guide Tween between the frames.
Solution d): This is a bug and it
happens occasionally, but I am not sure of the cause.
For some reason, a layer that is not indented will sometimes
be governed by a motion guide layer 2 or more layers above.
It may happen when you move layers up or down in the timeline
or when you remove a layer from under a guide layer. It
may also happen when you move a symbol from one layer
to another after it has shared the layer with another
symbol. For some reason, the Tween motion of the one level
[even without having a guide layer!!!],
will affect the motion on the other layer, causing the
symbol on that layer not to move as expected.
What to look for: a symbol on
one layer will not move as expected but will move in
one direction and then suddenly snap and jump to its
final point on the stage. The symbol on the other layer,
however, will operate as expected.
To solve this problem, check for Tween Symbols in your
library as in " problem c". Unfortunately, Flash doesn't
always create a Tween Symbol when you have the multiple
layer problem. You may need to copy the frames of the
offending layer, delete that layer, and create a new
layer above the guided layers and then paste, or you
may need to delete the layer and start over.
These are just a few of the little foxes
that cause endless headaches for even experienced Flash
developers. Next time: The Trouble with Buttons.
Jeff Peterson is a Macintosh pioneer,
acquiring his first 128k Mac in 1984. In 1993, he started
work on the Internet, producing an early e-magazine, O
Theophilus, and educational courses for the web.
He started his own web design company in 1999, www.PetersonSales.net
and is still acquiring new clients. Jeff is also a part-time
theologian,The
Scholar's Corner, and he loves to play Flight Sims
when he gets a chance, being part of the notoriousShadow
Riders, call sign Padre
=<SR>=.
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