How would I do the following

Detect cliffs (overhangs exct)
Fill in the air under them with gravel (or some other useless block)

 

I would just use worldedit....

 

if the (sky) light level is lower then 15, then there must be an block somewhere above

 

Then it would fill in caverns too...or wait that might work.

So go through every block...
Do that
and bang...

http://www.minecraftforum.net/topic/231255-worldpainter-new-map-creatorgenerator-work-in-progress/page__st__3920

 

if the light level is smaller that 15, but bigger than 0, fill it up

 

Code:

boolean foundBlock = false;
for (int y=255; y>=0; y--) {
    Location loc = new Location(getServer().getWorld("world"), 0, y, 0);
    if (foundBlock && loc.getType() == Material.AIR) loc.setType(Material.GRAVEL);
    if (loc.getType() != Material.AIR) foundBlock = true;
}

 

which would also affect caves with lava

 

If the light level is smaller than 15, bigger than 0, and above a certain altitude.

 

Caves can be at any level.

 

But lava lakes aren't.

 

EnvisionRed
I was meaning the sky light level, but I forgot to type sky

 

How do you intend to distinguish cliffs from cave entrances?

 

You've never seen a surface lava lake?

 

I have, but if you payed attention, those would not get covered up. They fail the check for altitude, and so will not be covered. Now would you kindly either offer some ideas for the OP, or gtfo this thread.

 

And why would they not be covered up? Again, they can occour at any level, so the altitude check is irrelevant.

 

I have never seen a lava lake on a mountain, only about sea level, though they might simply be rare. I have to support the height check though as cliffs do not exist below sea level (except for crevices if you count those as well) and checking blocks below would simply be a waste of ressources.

 

You have to think of the likely-hood of that. It's not possible to spare each and every single lava lake without doing way too many checks. And they would not get covered up if they are on the surface, as the light level is above zero. Honestly, you don't understand the problem here, and you aren't trying to offer ANY solution whatsoever.

 

I don't have to provide any kind of a solution whatsoever. I'm simply saying it won't work 100% of the time.

 

Well I guess ill have to have the world rendered without the cool overhangs -_-

 

Why do you want 'cool overhangs' filled with a useless block underneath?

 

So I can get rid of the useless blocks after the bo2's successfully rendered

 

So you want to prevent any bo2s from being placed under cliffs? Or is your terrain generator not properly checking whether there's enough space for the bo2s it's placing, possibly overriding cliffs?