How can one find ceilings, i.e. the bottoms overhangs?

[Alfamike]

Fit like abody?

I have been wondering about this before but never managed to find a solution.

My question is how to restrict a certain shader to the bottom of overhangs. The 'ceiling' of the overhang that you'd see when you're standing underneath it looking straight up. I think we'd need more variables in the distrib shader or surface layer shaders, but I might be wrong.

My thoughts have been going in the direction of somehow using shadows that are created by the sun, but that pretty much was where my latest idea stopped. Not been able to do anything with it.

Anybody who can shed some light on this? Much appreciated, as always.

Cheerio.
AM.

EDIT: I'm not wanting to render an image upside down, if that's what you jokers would like to suggest. 

[cyphyr]

I'm thinking that your after making stalactites and hanging ferns etc. Now this is a very good idea but I'm unsure how you'd do it. Its hard enough getting objects to populate verticle surfaces. Good luck, I hope someone has a solution.
Richard

[Alfamike]

I'm thinking that your after making stalactites and hanging ferns etc. Now this is a very good idea but I'm unsure how you'd do it. Its hard enough getting objects to populate verticle surfaces. Good luck, I hope someone has a solution.
Richard

Bastard  ..... yes, that's the idea. We'll see if the wise men come along.

[cyphyr]

I have a solution now, just rendering out the image and I'll post the tgd and simple object I used. Basically the only un-obvious part was that the object had to be turned upside down otherwise it did populate the overhang but did so within the rock surface !!
Bout half an hour ...
Richard

[bigben]

Try restricting the slope to >90 degrees?

[cyphyr]

Here you go, should be fairly self explanatory, but do ask if you have any q's. By the way the overhang is just a crater shader with a large displacement restricted by height.
Richard

[Oshyan]

Yes, use slope values greater than 90 degrees (or try negative values).

- Oshyan

[Alfamike]

Here you go, should be fairly self explanatory, but do ask if you have any q's. By the way the overhang is just a crater shader with a large displacement restricted by height.
Richard

Ace, guys!

The simple solutions are often the best and sometimes the only ones. I'll have a play with your TGD later today.

AM.

[Mohawk20]

I actually did a test with shaders that were only visible at the underside by using negative values, see example:

[Alfamike]

I actually did a test with shaders that were only visible at the underside by using negative values, see example:

Goedemorgen Mohawk20,

Stom dat ik niet aan negatieve hoeken heb gedacht, zat al met m'n kop in de functienoden naar normalen te kijken. Dit maakt het in ieder geval veel makkelijker.

AM.

[Alfamike]

This works fine when you restrict by slope, like mentioned before in this thread.

However, it does not show in the render preview.

AM.

[Alfamike]

This works fine when you restrict by slope, like mentioned before in this thread.

However, it does not show in the render preview.

AM.

I take that back. TG was in the process of crashing. Now, after a restart it does show up in the preview.

AM.