Hi all,
following my experimentation around cracks on rocks, I have developed this further to accomodate for two otherwise distinct effects in parallel:
1 - Make Gashes
I'm using the term "gashes" to refer to a type of cracks that happen with rocks that exist in environments with a big cold/hot gradient. These stones 'crack' open, leaving deep gashes on the surface.
2 - Make Cracks
In this context, I'm referring to sediments, layers of stone that chip off entirely.
Now, the function can generate both effects at the same time, and allows to favour one or the other, or mix them equally.
Note that the function is currently optimzed for fake stones of other objects with an average size of 3 meters. If you require another scale, you'll have to fiddle with the functions accordingly. It's best to change only one parameter at a time to understand their effects. (I know you will most likely change them altogether, but then, you have been warned ;-) )
The contant scalar on the voronoi accounts for the size of the 'cracks' pattern.
The "Adjusting the deeper gashes" node controls the gash structures, obviously.
Then, the "Make gashes and cracks" node controls how visible and deep the structures become. This is done in the displacement tab of the node.
Finally, there are a few other displacement-generating nodes which control the larger overall shape of the fake stone.
Oh, and there's an image map shader providing texture. I suggest you either use your own texture file, or use other ways of providing color to the stones.
Have fun,
Frank
PS: I'm continuing to work on a separate and more perfect "gashes" function together with Volker. Watch out for that.