How to attack a "shrink wrap effect"

[cheeko8080]

hi everyone,
i have an idea that i'd like to throw out there for anyone who either knows how to do this or has an idea of how to approach it. i dont know whether this would even be possible right now, but i think that it is somehow. this is the goal:
1. i'll have two objects in the scene with one inside the other (like a human head inside of a larger monster head)
2. when i scale the larger object inward, it scales inward until it reaches the smaller object
3. the larger object scales on a per vertex basis so that if one vertex of the larger object reaches the smaller object, then that vertex stops moving, but the other vertices that havent yet reached the surface continue to scale inward
4. this effect should acheive the look of shrink wrapping plastic over the smaller object, though i realize a really low poly mesh wouldnt acheive this, a sufficiently high poly mesh could get this look pretty well

Though i can't really think of how exactly to implement this, i was thinking that maybe an expression would work best but dont know how to get a vertex to understand that it has reached the surface of the other object. if anyone has any ideas on any part of this and would like to share or be interested in possibly working this out with me, please let me know. any other ways of doing this would be greatly appreciated, especially if it is a simpler way than having to code everything. thanks for checking this out.

-clint

[failure]

use blendshapes

[drblacksnake]

scale softbody's goal and make human head (or its lo-res version) colide particles.

[cheeko8080]

i mean i could use blendshapes if i make both with the exact same mesh and warp the one mesh into the second mesh...but i was trying to do this a way that is not so crude and involves an easier and less labor intensive when it comes to actually implementing it

[cheeko8080]

i totally get the concept of what your saying and it sounds like reasonable way to do it to me, however i am trying to think of actually implementing it and i think that i simply must not have enough experience with softbodies or collision particles because i have an issue with each. i didnt know that you could directly affect a softbody to scale, unless your saying that i should have the monster head (just to keep the example going) turn into a softbody and then simply key the scale at "1" at time 0 and then at a later time scale the head so that it is smaller then the human head and key it there. and if i do the human head as a collision object it should shrink wrap around the human head and not go inside it. my other issue is that you said collision particles, i'm not sure what you mean. I didn't realize that you could turn a polygon object into particles. I guess i'm just not clear on that one. Clarification would be awesome...thanks for getting back to my post...

[drblacksnake]

I just dropped to You an working idea. Press F1 to find out about what's under 'softBody' term. Learn how to help Yourself at most trivial cases. Although Yours is not such one, the way has been shown already.
Also, as failure mentioned, blendshapes might be helpful in case You want to do corrections for e.g. mosnter's mouth fit human's mouth etc..
Goodluck!

[pyrokinesis]

It seems to me that what you are describing, basically is "a soft-body problem," in the sense that you want one planar surface (the shrink-wrap) to follow another one. You don't care about gravity, inertia or any other forces that exert their influence in a straight line; only the attraction of one surface to another. And what you want to do (it seems to me), is to animate that attraction so that it increases over a short period of time. As the attraction between the shrink-wrap and the wrapped-surface increases, the shrink-wrap will lose all attempts at variation and will conform exactly to the surface.

To make this look good, you'll want to make sure that the number of vertices in each mesh is about the same; that the "density" of vertices is about the same. You'll need to pay close attention to the "lay of the land" and make sure that the wrap surface has enough points, in the right places, to conform smoothly.

Your handling of specular highlights on the two surfaces is going to be really important in making the whole effect "fly." For instance, you don't want to wrap a plastic surface with another plastic. If you're not careful, as the two surfaces get close to one another they can "merge" in a particularly jarring way that's hard to describe unless you see it happen: the 3D-illusion is broken.

Plan to use camera-cuts to your full advantage. For example, you probably want to have the shrink-wrap first be "approaching" the surface-to-be-wrapped, then show it tightening into place. A camera cut falls naturally here, and it can make your work a lot easier, because you can tackle each problem using separate techniques. If the audience sees this sticky stuff heading toward the protagonist, CUT TO the stuff finishing the act of tightening into place (and, ideally, acquiring some of the texture of the surface-being-wrapped... it's sticking that tightly... you'll have this shot "in the can" and I doubt you really want to do too much more. Getting wrapped in plastic is probably an idea you want to "get across clearly, but not belabor."

[failure]

As I already said - use blendshapes. It will give you best looking and most controlable results in reasonably short time.

[joojaa]

Poblem with shrinkwrapping is that it is realy realy very very crude to say the least.

Its pretty easy to do with softbodies in many different ways, but basicaly you loose all detail you had to begin with. Waht i would do is rebuild the second face by manualy snapping point correspondences on the esisting surface, the resulting geo is going to be much much cleaner, and it can even be animated with the rig you were planning to use.

heres wsomething im talking about:

it was ddoine by making the object soft with copy to soft and scaled goal down, made some springs to flow it a but out and tned goal down once i woas on surface. And the box was make particle coliding with friction as 0 and resilisence as 1.

[pyrokinesis]

That's basically why I suggested using camera-cuts aggressively. You want to convey the message that this clingy-stuff is going to be shrink-wrapped around an object but you really don't want to show the entire process. For one thing it would be a rather long sequence to park the camera on, and for another, if you actually did that it would look like one of those darned movie-CG sequences where you just feel like they've put it in, and in excruciating detail, just to show-off. The crinkling geometry isn't going to look good in-process, so you can probably get away with "this is about to happen" [CUT TO] the last one second. A very tight cut will convey the message without lingering and I think that would work best, in addition to being considerably easier. "If no one is going to be impressed outside of SIGGRAPH, cut it."