View Full Version : Tearing down a concrete wall
04 April 2007, 11:03 AM
What I need to do is break down a wall made of concrete. It's basically a cube that needs to start cracking from its top. The cracks grow bigger and bigger, chunks of concrete fall the the ground and in the end the whole wall has dissolved to more or less small pieces lying on the ground.
How would go about this? I'm a bit lost here.
04 April 2007, 09:33 AM
Within XSI a combination of keyframe/shape animation, particles and rigid bodies come to mind if it all has to be īn camera". Otherwise you might can do some creative editing to "get away" with some stuff.
I've done some stuff like this a while a go, but in Maya with the blastcode plugin. It was pretty easy to use and had good results. It's too bad there's still no XSI version of it.....
04 April 2007, 01:57 PM
Oh, I'd love to see Blastcode for XSI. That would be awesome.
04 April 2007, 02:12 PM
I can recall something about a standalone version -that would read/write to maya, max, xsi and lightwave(?)- when they moved over to the AGEAI engine. Haven't seen or heard anything on this after the announcement of the 1.5 version. Will have a look into that rumour again.
04 April 2007, 02:52 PM
From what I understand of Blastcode (i've never used it but had a look at the examples) it has some kind of 'crack' generator which one could use Michelle Sandroni's excellant shatter addon which can be found here (http://www.motionblur.it) or you could generate the cracks yourself with boleans.
If you look at some of the example quicktimes on blastcode site the cracked geometry then replaces the original geometry at a specified frame heres an example (http://www.blastcode.com/gallery/sample.php?pid=108) and uses a RBD engine to simulate pieces falling and bouncing off the ground. Additionally there are particle fragments emitted from the hole geometry. All of this can be accomplished easily from within XSI with a bit of planning. Granted its not an automated solution, but overall will give you much more control and flexability.
What you have to watch out for, and is a common mistake, is trying to simulate all the broken geometry in an 'unbroken' stage- I notice that Blastcode doesnt do this but switches out to a semi broken state from within 1 frame. this is to help the poor engine, if the objects are too close together then the Rigid Bodies simulation cannot compute the pieces, (unless an incredibly high accuracy is given) so I find it best to help it on its way by moving the pieces in the direction they should be going in first and then simulating from that frame and its keyframed motion. - another way to accomplish this is to use hidden sphere obstacles which would 'push' out the objects in the right direction.
From what you describe you would need a few staggered stages, and again if you look at the example movies at blastcode, this is pretty much what it does, progressively break up the original geomtery and swap out the geometry over successive frames.
This can be a fun thing to do once you got the basic process organised in your head. start simple and work your way up. If you get stuck, give us a shout and if I have time I'll try and setup a sample scene
04 April 2007, 08:40 AM
i should keep an eye on this thread. this is an effect i've wanted to do for a while. don't need to right now but might as well follow it up now so i dont have to do this later.
04 April 2007, 09:53 PM
From what I understand of Blastcode (i've never used it but had a look at the examples) it has some kind of 'crack' generator which one could use Michelle Sandroni's excellant shatter addon which can be found here (http://www.motionblur.it/) or you could generate the cracks yourself with boleans.
I found that just breaking up the objects was the hardest part. The problem I found with the shatter addon is that the current version doesn't jitter the broken edges, so they are perfectly straight, and the older versions doesn't leave any gaps between the surfaces, which makes them unsuatable for RBD simulations. It also takes a lot of work to get the crack directions to look decent. I found I had to rotate the objec(s) by hand after each pass, of the cracks would look very unnatural. This pretty much leaves you with breaking up the surfaces by hand, which is a pain. If anyone has a better solution to doing this I would be very interested.
04 April 2007, 09:59 AM
how do you break it up by hand?
04 April 2007, 02:30 PM
I recently have done this for a TV spot. It was more of an explosion though.
The problem with the technique I used is it nice for a wall or something that breaks up in pieces all the way through the volume. It doesnt work for something that breaks up half way up the some more and then all the way through.
Here is a summary:
1. Duplicate the object you want to break up while still in its planar form (for wall its a plane, duh.)
2. Tesselate the object, preferably into triangles
3. Select the edges that make the pieces boundaries
4. Disconnect them
5. Add a Smooth modifier (set at 0)
6. Extrude all the polys
7. Make Clusters of the individual pieces
8. Add a weight map
9. Connect the weight map to the smooth modifier
10. Animate the weight map as revealing the cracks (the smooth modifier will make poly islands seperate from each other)
11. Animate the individual clusters (pieces) with a cluster center deform
Its pretty basic, but it works. The most time consuming part is the cluster assigment. This could be scripted though.
Here is an example. Its a wip from the project so dont expect miracles.
04 April 2007, 02:30 PM
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