Feature/land mesh2

[martindevans]

Main change is that the landscape now has normal data (Resolve #27).

• This generates a map for all pixels in the heightmap except a one px border all around. This is so that the pixels from the next tile over can be stored there (allowing seamless normals).
• Rewritten generation to be based on iterators. I was planning to use parallel iterators etc to generate all data channels simultaneously, but that turned out to be a pain in the ass.

Also some other changes that will make implementing #31 (my next task) easier:

• Wrapped heightmap data sources in a HeightmapData trait. This allows heightmaps to be stored in things besides textures (e.g. a 2D array downloaded form the server).
• Implemented HeightmapData for a wrapper around textures (still requires 8bit grayscale textures only).

[martindevans]

Clippy was failing due to one warning (many_single_char_names), I've added a longer name to satisfy clippy but this warning will need some reconfiguring in the future.

[Jerald]

Having raw numbers exposed in an api, especially an external one, is somewhat scary to me. It's relatively brittle and lends itself to accidentally misusing things.

[martindevans]

raw numbers ... public API

The main API surface is:

let wrap = TextureHeightmap::new(textures.get(&land_texture_handle).expect("Couldn't get texture")).expect("Couldn't wrap texture");
let land_mesh = texture_to_mesh(&wrap).expect("Couldn't turn texture to mesh");

HeightmapData (the main place numbers are exposed) is ultimately only really going to be used within the mesh generation system.

[Jerald]

I was mostly referring to the fact that the structures themselves are marked as pub and are therefore accessible externally. Either way, we can leave things as they are now. If issues come up, I think we know a place to possibly put some work.

[martindevans]

[martindevans]

I was mostly referring to the fact that the structures themselves are marked as pub

Ideally the entire landscape meshing system would be contained within a separate crate to the rest of the game and the HeightmapData trait will be an implementation detail. I'll be doing more work on more advanced mesh generation in a followup PR (after we've changed to a workspace) so I might see if I can rearrange things to be nicer then.

[Nyefari]

The only weird thing I had noticed before you've already fixed. Should have submitted the review yesterday, sorry.