Anyhow, other than adding in what was strictly necessary to get things working (like adding falling blocks of the various materials that get eroded) I also changed all the default dirt blocks (and their eroded slope varients) to make them fall. Between that and the way things get eroded at pretty much the slightest excuse, it's overall a bit harder to play (though you can walk around without needing to jump nearly so much, which is somewhat nice). I'm hoping to eventually make the slope formation rules generate better looking terrain, right now it's still pretty very...angular looking. Generally pretty walkable, but not as visually appealing as I want (Edit: I'm probably not going to get the terrain generation looking too much better than it is now...it already feels like I'm pushing my luck with performance).
Edit: I forgot to mention that the loose dirt/sand/gravel you collect can be crafted back into full blocks (Four of them make one block of the original material, the recipe is shapeless since you can't make anything else with them...you can also place them directly, but they're a bit frustrating to try and use to actually build anything other than a sloped pile). You can also craft sloped cobble into microblocks without needing the exactly corresponding slope, though this results in some lost material. In this version you might notice that there is a noticeable overall loss of the various erosion materials as they fall on each other and stuff, this will never be fixed entirely is normal and expected (the materials being lost are renewable within the mechanics of the mod, and not terribly valuable anyway), but it will hopefully somewhat less obvious in future versions.
This is currently (and probably forever?) a really simple mod, just a depends.txt and an init.lua, available at the Github link below (along with a readme and license, but that has less information than this post). I have no plans to add additional elements, though support for some other mods is possible if that's desired.
Some screenshots of the current results: Current
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This should be considered an super early version, subject to change, try it out on a new world and don't get too attached because improving the slope formation rules may not apply well to already eroded slopes (I mean, there is a chat command added to the trial version which enables slope generation in existing mapchunks--thanks to help from paramat--but it doesn't do the surface slopes and has an issue when used above ground probably/hopefully they will, but I'm not sure yet, I'm now pretty sure I can't get the voxelmanip to work with anything that's already been generated, but I'm not planning on making any more major changes to it at this point).
Edit: I made some revisions of how the slopes form, it's not perfect but I feel it's better. I also revised the ABMs and stuff...made it so falling dirt/gravel won't make stone and such erode. It's kinda fun to just use loose dirt to make a big dirt pile, though I need some more revisions.
It's been suggested that I alter the map generation and use VoxelManip to do more of the generation without relying on ABMs and LBMs, but this is currently beyond my experience. I think it's a good idea and I'm going to work on that, but it may not happen particularly soon. This most recent version fixes some issues and makes the terrain a little smoother. I now have a working map generation function, but it seems like it might be pretty crude, both in that I don't know a good way to identify where stone is exposed to air other than by checking every node and because the surface terrain is not as smooth as I would like (obviously what I would like would be perfectly simulated reality, probably not going to get there).
I decided that the underwater slopes were more problematical than helpful, they don't really alter gameplay or visual sense and they do impair performance. I might do something with a "surf zone" in the nodes just below water once I figure out how to use minetest.get_mapgen_object() properly...I think I'll go with making it so that the surface layer of water is replaced with flowing water and letting the waves lap against a level beach, but that's all in the future...and probably best handled by a separate mod. For now I just have a few more tweaks.
View or download from Github
Even more experimental version
Outdated early version
The trial version has a chat command "erosion_slope_gen" which generates sloped stone in caves and such for an existing mapchunk (which may not have them due to being generated before the erosion mod was enabled). This requires the user to have the privs noclip, server, and rollback (server and rollback because it can make significant changes to the mapchunk, noclip because otherwise you can totally get trapped). It has an issue I couldn't fix when used at the surface (generates a line of sloped stone hanging in the air) and isn't really necessary.
Note that the code is still super-unlicensed, in case you want to assist me with keeping up my three felonies a day. Turns out that if you create a file called "license.txt" on Github, they provide a selection of template licenses you can use. Among them MIT. Which reminds me, I have been to Boston in the fall...among other things.
License: MIT
Dependencies: default, moreblocks
Optional Dependencies: farming
I'm considering whether it is possible and desirable to add support for some other mods, like Ethereal, which add their own turf blocks. I'm not particularly convinced it is all that necessary. As it is there is a tendency for landslides to start spontaneously and when they are too large they result in significant framerate drops and often large numbers of items which need to be cleaned up by the engine. In fact some players may find it useful to comment out the ABMs (I should provide better comments on what each does, for now it's enough to know that there are four of them and the bottom two are likely to have more impact--one of those is commented out already).
