Shape keys and extrusion

Hi folks !
Here is my problem, i want to animate a mesh extrusion, something like “crawling rust” in horror movie. I tried to use the shape keys but whith this tool, all the vertices need to exist at the first time.

How can i “complexify” a mesh during the animation to perform this effect ?

Is it possible to add vertices (by extrusion) to a shape key without altering the base key ?

Please help !

You might be better off using an animated texture, possibly using an empty as the map to, and animating the position of the empty at specific frames - you could then also key the mapping of the normal to make it deepen as it progresses. Check Cyborg Dragon’s texture threads, as well as Cog’s texture tutorials if this is all new. It would be easier in my opinion to use this method, since you won’t have to worry about alignment of all those base vertices that would be necessary to shape key the changes.

One approach might be to start with a voronoi texture set to the right color band and set to nor on the mapping, and then use a blend texture set to stencil, mapped to an empty. The blend could act as a reveal of the voronoi, and this might help make the surface extrusion look real. The mesh would need to be subsurfed beforehand.

You’re right.

Thanks for your advices. Cog’s texture could be an answer to particular situations (crawling rust in this case), but i need something more managable at the mesh level (remember this old movie “The Blob” growing and acting).
I sent this thread to the developement forum at It might be interesting for future builds.
The point would be to allow each new shape key to be independant of the base mesh and considered a new base key for the modified mesh without altering the previous steps.
Anyway thanks for your time.

Perhaps a fluid simulation could be helpfull here?

I would suggest looking into the effects used in the modern flubber disney stuff, and also realize that what you are asking is achievable in different forms, different methods like fluids, softbodies,textures, actual shape keys, etc.

Read up on what you are wanting to do and take the time to see how the experts achieve those results. Then learn how to reproduce this in your preferred software(s).