Mesh builder

[ManevilleF]

Closes #77

Work done

• complete rework of mesh procedural generation
• MeshInfo struct can be merged with other meshes (@alice-i-cecile )
• Added a ColumnMeshBuilder for column meshes
• Added a PlaneMeshBuilder for plane meshes
• Add a mesh_builder example showcasing builder options

[ManevilleF]

@alice-i-cecile what do you think of the builder API ?

Also, I wonder if I should remove the cheap column I doubt anyone is using it

[alice-i-cecile]

Builder API is nice, although I'd probably make the fields pub. I'd actually keep the cheap hex mesh around: it's useful for creating bounding columns for picking.

[ManevilleF]

@alice-i-cecile all done, could you check that this PR doesn't break anything in emergence ? Also you might be able to remove the bottom face now and save a few triangles

[alice-i-cecile]

Yeah, lemme try out a migration :)

[alice-i-cecile]

Experiments:

• using deprecated methods still works
• using new mesh builder works
• using mesh merging works

Mesh merging with its current API is not very useful at all:

• it's very easy to hit the u16::MAX limit
• there's no way to specify the translation offsets of the meshes in advance, so they end up collapsed into am overlapping pile
• I really want to be able to call .reduce with merge_mesh but the type signature is wrong

IMO cut mesh merging from this PR and release.

[ManevilleF]

The mesh merging method was mostly created for inner usage, it is used by the build method of the new builders and allow to compute different parts of meshes separately.
For your use case, merging all your map together would indeed require a lot of offsets.
I'll investigate looking at the emergence MR to see if I can bring a quick win but otherwise I'll make that method private for now until I start working on chunking

[ManevilleF]

I added comments to your test attempt, I think you are missing a single param for merging to work as expected.

About the u16 limit, I could consider indices to be u32 but I don't think merging such large meshes make sense, as they should be merged as chunks anyway, otherwise the AABB optimizations in rendering wouldn't apply

[alice-i-cecile]

Agreed on the chunking point: I wanted to test it out quick and see how it works :)