Re: FLASH: 3D vector Animation

[John Dowdell]

At 11:13 AM 8/25/98, "Richard Ortega (EML)" (by way wrote:

>Can anybody help me with creating 3D Vector animation in Flash.  I am

>using tweening to create sophisticated rotation but the animation is not

>as smooth as I would like.  The problem occurs when I use shape hints as

>the animation seems to vary in size throughout the tweening.  I would

>like the shapes to keep a consistent size.


If you're trying to take tracings of 3D shapes and then appear to 3D-rotate

them by tweening, then that won't go. Here's a try to explain why.... <g>


In 3D animation you usually define a solid body, with each corner a certain

XYZ distance from the object's origin. When you rotate the object only the

origin moves, and each vertex retains its original relationship with the

object's center. With each frame this 3D space is projected upon the 2D

screen (with depth-correction). It is this 2D projection you're tracing.


The shape-morphing in Flash does (pretty much) point-to-point linear

interpolation between vertices in the 2D plane. This does not have access

to the original 3D structure of the object -- it only knows about how the

3D object looked when projected upon the screen. Therefore the 3D shape

won't "hold"... it will seem to shift, because there's no real 3D space

there, just a 2D picture.


As an example, if you extrude a letter and spin it in 3D space, then an

edge won't do a straight linear morph on the screen. It will actually use a

sine-related rate of motion, because the shape is actually spinning, and

the rate of motion depends on the angle to the viewer. These things are

hard to interpolate by linear screen-based interpolation... there's not

enough information in the screen to know the structure of the 3D object.


Flash's great strength is in 2D vector animation. It can use bitmaps, and

sound, and can simulate 3D shapes, but it doesn't really do 3D

interpolation of solid bodies, regrets. For 3D illusions the best may be to

make a clip of a series of changing shapes, rather than try to do

3D-tweening in a 2D program.


jd




John Dowdell, Macromedia Tech Support, San Francisco CA US


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