Things to be Observed and then documented somewhere in a wiki.

[LexiBigCheese]

Observe: RGBA8 Textures with side lengths larger than 1024 do not work, does this apply to other formats?
Observe: What Texenv Source::TextureN outputs when a Texture is not bound
Observe: The contents of a Texture before any data is uploaded to it
Observe: The contents of each mip level of a mipmapped Texture before data is uploaded to it
Observe: The contents of each mip level of a mipmapped Texture after data is uploaded to it, but before mipmaps are generated.
Observe: The maximum number of uniforms a shader can handle (And a translation for how many bones you can expect to have in a shader, as well as an example for how to implement ordinary skinning and dual quaternion skinning, and how many bones you can have there)

[LexiBigCheese]

Ah, there are:
96 (0x60) FVec ([f32;4] in PICA order) uniforms, which equates to 24 matrices,
4 IVec ([i32;4] in PICA order) uniforms, and
16 boolean uniforms.

So model authors, or more specifically rig authors should try to keep an individual rig below 16 bones, if the developer is using ordinary vertex skinning techniques in which you have vertex attributes

struct Vertex<N:usize> {
  ...,
  bone_indices: [i32;N],
  bone_weights: [f32:N],
}

where N is usually 2, 3, or 4 (and for the 3DS, I expect 4 will be overkill)
to go from a vertex position point to a skinned point, perform in your vertex shader, where bones is a uniform containing a lot of matrices,
but the matrices aren't the bones position relative to the root bone, they're the bone's transformation relative to the bone's original position (in blender, the original position is the position the bone shows up in during edit mode)

(0..N).map(|N| bones[bone_indices[N]].transform(point) * bone_weights[N]).sum()

note: this is pseudocode, more advanced knowledge of vertex skinning will be required to know the bone matrices to send to the 3DS.

If you're using dual quaternion skinning, you can double the number, as each bone in dual quaternion skinning only needs 8 f32s.

Also note that the bone weights could probably be u8 instead, if you so desire.

Also note that if you need more bones, you can always split a model up, share a few bones between the two meshes, and render that.

[ian-h-chamberlain]

Hi @LexiBigCheese, thanks for writing up all these notes / ideas somewhere! I haven't been super active recently but I'm glad to see some other people still interested in and working on 3DS graphics stuff 😄

I'm going to move some issues (like this) that don't seem like bugs or feature requests into discussions so that it's easier to keep track of what's what, but please feel free to continue posting notes and ideas there if you'd like!

Adding/creating a wiki isn't a bad idea, GitHub wikis are little awkward to use but I may look into setting up one for this repo like we have for ctru-rs.