View Full Version : Growing cracks on a wall.

09-21-2008, 07:54 PM
I'm working on a visual effects shot of a ceiling that I need to grow a crack on. There's an existing crack that spreads, and eventually the ceiling collapses down, with lots of pieces and plaster smoke and all that.

I've tried several techniques to model the crack but I'm just not getting realistic results. I tried modeling the crack myself but I'm having two problems. 1) The path of the crack doesn't look realistic and 2) the edges of the crack look too even. I even tweaked the edges a lot and I'm still getting something that doesn't look realistic.

To get it to grow, I rendered a plain ceiling, then layered my crack render over top of it and revealed it in After Effects, which kind of worked. See the attached video.

What I would like to do, is use an actual crack image projected onto my CG ceiling object in like "Darken" mode, or some other kind of blending mode to get it to blend in. Then use the same image for a bump or displacement map. Then I could trace out the crack in modeler, and drop the pieces how I want.

I'm shooting for the look in the following commercial:

http://www.metacafe.com/watch/1283564/nutrition_education_ceiling/ (Let the first advertisement play.)

They really nailed the edges and the bumpiness of the crack, I'm figuring they used some kind of bump/displacement map. I think they did the reveal just using a similar tracing method in a compositing program. In my video, I'm also revealing some procedural texture bumpiness that isn't working and my reveals are out of sync. I plan on fixing that.

I feel my crack just looks to "thick". And it's too hard to model it manually to the fine details that I need. I think I need to go with an image. I checked CG Textures but didn't see any good images of cracks. Any suggestions or guidance?

09-22-2008, 11:56 AM
Im sure there is a good way just using morphs..IŽll bet splinegod has some tips on how to do it without plugins..havenŽt had time or need to do it myself thou.
otherwise you can check this plugin a tutorial on doing cracks using smart morph.



09-22-2008, 08:11 PM
That helps with the growing of the crack, but I think the harder part is the look of the crack. I think I'm going to try to use an image layered onto the surface. I found a tutorial by Andrew Kramer where he does it. This is the shot he creates, you can see the crack in the ground briefly:


William Vaughan has a video where he shows how to do something similar to SmartMorph. But like I said, it's the edgy, bumpy look of the crack that I'm going for. I just can't seem to get it modeling by hand.

Still curious if anyone knows how they did it in the commercial in link from my original thread.

09-22-2008, 08:27 PM
The attached image is an example of the type of crack image I'm going to try to make. This is what is used in the above shot. In his tutorial, he says he Photoshop'd it from several other images.

09-22-2008, 08:27 PM
Can't you just use a clip map if the crack is fairly simple?

09-23-2008, 07:16 AM
A clip map to do what, animate the crack? At this point, it's less about animating the crack and more about the look of the crack. I'm still curious how they got the look in the commercial in my first entry.