Generation and Iterator Expressions

Meshes can be generated from primitives like cubes and spheres using iterator expressions. Primitives emit topological structures like Triangles or Quads, which contain arbitrary geometric data in their vertices. These can be transformed and decomposed into other topologies and geometric data via triangulation, tesselation, and conversion into rendering pipeline data.

```rust use nalgebra::Point3; use plexus::buffer::conjoint::ConjointBuffer; use plexus::generate::sphere; use plexus::prelude::*; // Common traits.

// Example module in the local crate that provides rendering. use render::{self, Vertex};

// Construct a buffer of index and vertex data from a sphere primitive. let buffer = sphere::UVSphere::::withunitradius(16, 16) .polygonswithposition() .mapvertices(|vertex| -> Point3<_> { vertex.into() }) .mapvertices(|vertex| vertex * 10.0) .mapvertices(|vertex| -> Vertex { vertex.into() }) .collect::>(); render::draw(buffer.asindexslice(), buffer.asvertex_slice()); ```

Half-Edge Graph Meshes

Generators are flexible and easy to use, but only represent vertex geometry and are difficult to query and manipulate once complete. A Mesh, represented as a half-edge graph, supports arbitrary geometry for vertices, edges, and faces. The graph can also be queried and manipulated in ways that generators and iterator expressions cannot.

```rust use nalgebra::Point3; use plexus::generate::{sphere, LruIndexer}; use plexus::graph::{FaceKey, Mesh}; use plexus::prelude::*;

// Construct a mesh from a sphere primitive. The vertex geometry is convertible // to Point3<f32> via the FromGeometry trait in this example. let mesh: = sphere::UVSphere::::withunitradius(8, 8) .polygonswithposition() .collectwithindexer::>, >(LruIndexer::default()); // Extrude a face in the mesh. let face = mesh.facemut(FaceKey::default()).unwrap(); let face = face.extrude(1.0).unwrap(); ```

Hashing Floating-Point Values

When collecting an iterator expression into a graph or buffer, an indexer is used to transform the geometry into raw buffers. HashIndexer is fast and reliable, and is used by collect (which can be overridden via collect_with_indexer). However, geometry often contains floating point values, which do not implement Hash. This means some thought is required when collecting iterator expressions: which indexer is used and what types are involved?

The ordered-float crate is used by the ordered module to ease this problem. Common geometric types implement traits that provide conversions to and from a conjugate type that implements Hash.

The ordered module also exposes some hashing functions for floating point primitives, which can be used to directly implement Hash. With the derivative crate, floating point fields can be hashed using one of these functions while deriving Hash. The Vertex type used in the above example could be defined as follows:

```rust use plexus::ordered;

[derive(Derivative)]

[derivative(Hash)]

pub struct Vertex { #[derivative(Hash(hashwith="ordered::hashfloat_array"))] pub position: [f32; 3], } ```