Split out bevy_mesh from bevy_render (bevyengine#15666)

# Objective

- bevy_render is gargantuan

## Solution

- Split out bevy_mesh

## Testing

- Ran some examples, everything looks fine

## Migration Guide

`bevy_render::mesh::morph::inherit_weights` is now
`bevy_render::mesh::inherit_weights`

if you were using `Mesh::compute_aabb`, you will need to `use
bevy_render::mesh::MeshAabb;` now

---------

Co-authored-by: Joona Aalto <jondolf.dev@gmail.com>

crates/bevy_animation/src/lib.rs

@@ -1244,7 +1244,7 @@ impl Plugin for AnimationPlugin {
                     // `PostUpdate`. For now, we just disable ambiguity testing
                     // for this system.
                     animate_targets
-                        .after(bevy_render::mesh::morph::inherit_weights)
+                        .after(bevy_render::mesh::inherit_weights)
                         .ambiguous_with_all(),
                     trigger_untargeted_animation_events,
                     expire_completed_transitions,

crates/bevy_mesh/Cargo.toml

@@ -0,0 +1,37 @@
+[package]
+name = "bevy_mesh"
+version = "0.15.0-dev"
+edition = "2021"
+description = "Provides mesh types for Bevy Engine"
+homepage = "https://bevyengine.org"
+repository = "https://github.com/bevyengine/bevy"
+license = "MIT OR Apache-2.0"
+keywords = ["bevy"]
+
+[dependencies]
+bevy_asset = { path = "../bevy_asset", version = "0.15.0-dev" }
+bevy_image = { path = "../bevy_image", version = "0.15.0-dev" }
+bevy_math = { path = "../bevy_math", version = "0.15.0-dev" }
+bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", features = [
+  "bevy",
+] }
+bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev" }
+bevy_transform = { path = "../bevy_transform", version = "0.15.0-dev" }
+bevy_mikktspace = { path = "../bevy_mikktspace", version = "0.15.0-dev" }
+bevy_derive = { path = "../bevy_derive", version = "0.15.0-dev" }
+bevy_utils = { path = "../bevy_utils", version = "0.15.0-dev" }
+
+# misc
+bitflags = { version = "2.3", features = ["serde"] }
+bytemuck = { version = "1.5" }
+wgpu = { version = "22", default-features = false }
+serde = { version = "1", features = ["derive"] }
+hexasphere = "15.0"
+thiserror = "1.0"
+
+[lints]
+workspace = true
+
+[package.metadata.docs.rs]
+rustdoc-args = ["-Zunstable-options", "--generate-link-to-definition"]
+all-features = true

crates/bevy_render/src/mesh/mesh/conversions.rs → crates/bevy_mesh/src/conversions.rs

@@ -4,15 +4,15 @@
 //! # Examples
 //!
 //! ```
-//! use bevy_render::mesh::VertexAttributeValues;
+//! use bevy_mesh::VertexAttributeValues;
 //!
 //! // creating std::vec::Vec
 //! let buffer = vec![[0_u32; 4]; 10];
 //!
-//! // converting std::vec::Vec to bevy_render::mesh::VertexAttributeValues
+//! // converting std::vec::Vec to bevy_mesh::VertexAttributeValues
 //! let values = VertexAttributeValues::from(buffer.clone());
 //!
-//! // converting bevy_render::mesh::VertexAttributeValues to std::vec::Vec with two ways
+//! // converting bevy_mesh::VertexAttributeValues to std::vec::Vec with two ways
 //! let result_into: Vec<[u32; 4]> = values.clone().try_into().unwrap();
 //! let result_from: Vec<[u32; 4]> = Vec::try_from(values.clone()).unwrap();
 //!
@@ -24,7 +24,7 @@
 //! assert!(error.is_err());
 //! ```
 
-use crate::mesh::VertexAttributeValues;
+use super::VertexAttributeValues;
 use bevy_math::{IVec2, IVec3, IVec4, UVec2, UVec3, UVec4, Vec2, Vec3, Vec3A, Vec4};
 use thiserror::Error;
 

crates/bevy_mesh/src/index.rs

@@ -0,0 +1,137 @@
+use bevy_reflect::Reflect;
+use core::iter::FusedIterator;
+use thiserror::Error;
+use wgpu::IndexFormat;
+
+/// A disjunction of four iterators. This is necessary to have a well-formed type for the output
+/// of [`Mesh::triangles`](super::Mesh::triangles), which produces iterators of four different types depending on the
+/// branch taken.
+pub(crate) enum FourIterators<A, B, C, D> {
+    First(A),
+    Second(B),
+    Third(C),
+    Fourth(D),
+}
+
+impl<A, B, C, D, I> Iterator for FourIterators<A, B, C, D>
+where
+    A: Iterator<Item = I>,
+    B: Iterator<Item = I>,
+    C: Iterator<Item = I>,
+    D: Iterator<Item = I>,
+{
+    type Item = I;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self {
+            FourIterators::First(iter) => iter.next(),
+            FourIterators::Second(iter) => iter.next(),
+            FourIterators::Third(iter) => iter.next(),
+            FourIterators::Fourth(iter) => iter.next(),
+        }
+    }
+}
+
+/// An error that occurred while trying to invert the winding of a [`Mesh`](super::Mesh).
+#[derive(Debug, Error)]
+pub enum MeshWindingInvertError {
+    /// This error occurs when you try to invert the winding for a mesh with [`PrimitiveTopology::PointList`](super::PrimitiveTopology::PointList).
+    #[error("Mesh winding invertation does not work for primitive topology `PointList`")]
+    WrongTopology,
+
+    /// This error occurs when you try to invert the winding for a mesh with
+    /// * [`PrimitiveTopology::TriangleList`](super::PrimitiveTopology::TriangleList), but the indices are not in chunks of 3.
+    /// * [`PrimitiveTopology::LineList`](super::PrimitiveTopology::LineList), but the indices are not in chunks of 2.
+    #[error("Indices weren't in chunks according to topology")]
+    AbruptIndicesEnd,
+}
+
+/// An error that occurred while trying to extract a collection of triangles from a [`Mesh`](super::Mesh).
+#[derive(Debug, Error)]
+pub enum MeshTrianglesError {
+    #[error("Source mesh does not have primitive topology TriangleList or TriangleStrip")]
+    WrongTopology,
+
+    #[error("Source mesh lacks position data")]
+    MissingPositions,
+
+    #[error("Source mesh position data is not Float32x3")]
+    PositionsFormat,
+
+    #[error("Source mesh lacks face index data")]
+    MissingIndices,
+
+    #[error("Face index data references vertices that do not exist")]
+    BadIndices,
+}
+
+/// An array of indices into the [`VertexAttributeValues`](super::VertexAttributeValues) for a mesh.
+///
+/// It describes the order in which the vertex attributes should be joined into faces.
+#[derive(Debug, Clone, Reflect)]
+pub enum Indices {
+    U16(Vec<u16>),
+    U32(Vec<u32>),
+}
+
+impl Indices {
+    /// Returns an iterator over the indices.
+    pub fn iter(&self) -> impl Iterator<Item = usize> + '_ {
+        match self {
+            Indices::U16(vec) => IndicesIter::U16(vec.iter()),
+            Indices::U32(vec) => IndicesIter::U32(vec.iter()),
+        }
+    }
+
+    /// Returns the number of indices.
+    pub fn len(&self) -> usize {
+        match self {
+            Indices::U16(vec) => vec.len(),
+            Indices::U32(vec) => vec.len(),
+        }
+    }
+
+    /// Returns `true` if there are no indices.
+    pub fn is_empty(&self) -> bool {
+        match self {
+            Indices::U16(vec) => vec.is_empty(),
+            Indices::U32(vec) => vec.is_empty(),
+        }
+    }
+}
+
+/// An Iterator for the [`Indices`].
+enum IndicesIter<'a> {
+    U16(core::slice::Iter<'a, u16>),
+    U32(core::slice::Iter<'a, u32>),
+}
+
+impl Iterator for IndicesIter<'_> {
+    type Item = usize;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self {
+            IndicesIter::U16(iter) => iter.next().map(|val| *val as usize),
+            IndicesIter::U32(iter) => iter.next().map(|val| *val as usize),
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        match self {
+            IndicesIter::U16(iter) => iter.size_hint(),
+            IndicesIter::U32(iter) => iter.size_hint(),
+        }
+    }
+}
+
+impl<'a> ExactSizeIterator for IndicesIter<'a> {}
+impl<'a> FusedIterator for IndicesIter<'a> {}
+
+impl From<&Indices> for IndexFormat {
+    fn from(indices: &Indices) -> Self {
+        match indices {
+            Indices::U16(_) => IndexFormat::Uint16,
+            Indices::U32(_) => IndexFormat::Uint32,
+        }
+    }
+}

crates/bevy_mesh/src/lib.rs

@@ -0,0 +1,58 @@
+// FIXME(15321): solve CI failures, then replace with `#![expect()]`.
+#![allow(missing_docs, reason = "Not all docs are written yet, see #3492.")]
+#![allow(unsafe_code)]
+
+extern crate alloc;
+extern crate core;
+
+mod conversions;
+mod index;
+mod mesh;
+mod mikktspace;
+pub mod morph;
+pub mod primitives;
+pub mod skinning;
+mod vertex;
+use bitflags::bitflags;
+pub use index::*;
+pub use mesh::*;
+pub use mikktspace::*;
+pub use primitives::*;
+pub use vertex::*;
+
+bitflags! {
+    /// Our base mesh pipeline key bits start from the highest bit and go
+    /// downward. The PBR mesh pipeline key bits start from the lowest bit and
+    /// go upward. This allows the PBR bits in the downstream crate `bevy_pbr`
+    /// to coexist in the same field without any shifts.
+    #[derive(Clone, Debug)]
+    pub struct BaseMeshPipelineKey: u64 {
+        const MORPH_TARGETS = 1 << (u64::BITS - 1);
+    }
+}
+
+impl BaseMeshPipelineKey {
+    pub const PRIMITIVE_TOPOLOGY_MASK_BITS: u64 = 0b111;
+    pub const PRIMITIVE_TOPOLOGY_SHIFT_BITS: u64 =
+        (u64::BITS - 1 - Self::PRIMITIVE_TOPOLOGY_MASK_BITS.count_ones()) as u64;
+
+    pub fn from_primitive_topology(primitive_topology: PrimitiveTopology) -> Self {
+        let primitive_topology_bits = ((primitive_topology as u64)
+            & Self::PRIMITIVE_TOPOLOGY_MASK_BITS)
+            << Self::PRIMITIVE_TOPOLOGY_SHIFT_BITS;
+        Self::from_bits_retain(primitive_topology_bits)
+    }
+
+    pub fn primitive_topology(&self) -> PrimitiveTopology {
+        let primitive_topology_bits = (self.bits() >> Self::PRIMITIVE_TOPOLOGY_SHIFT_BITS)
+            & Self::PRIMITIVE_TOPOLOGY_MASK_BITS;
+        match primitive_topology_bits {
+            x if x == PrimitiveTopology::PointList as u64 => PrimitiveTopology::PointList,
+            x if x == PrimitiveTopology::LineList as u64 => PrimitiveTopology::LineList,
+            x if x == PrimitiveTopology::LineStrip as u64 => PrimitiveTopology::LineStrip,
+            x if x == PrimitiveTopology::TriangleList as u64 => PrimitiveTopology::TriangleList,
+            x if x == PrimitiveTopology::TriangleStrip as u64 => PrimitiveTopology::TriangleStrip,
+            _ => PrimitiveTopology::default(),
+        }
+    }
+}