Add a UV sphere implementation (bevyengine#1887)

Added a UV sphere implementation

crates/bevy_render/src/mesh/shape/mod.rs

@@ -268,7 +268,9 @@ impl From<Plane> for Mesh {
 mod capsule;
 mod icosphere;
 mod torus;
+mod uvsphere;
 
 pub use capsule::{Capsule, CapsuleUvProfile};
 pub use icosphere::Icosphere;
 pub use torus::Torus;
+pub use uvsphere::UVSphere;

crates/bevy_render/src/mesh/shape/uvsphere.rs

@@ -0,0 +1,91 @@
+use crate::{
+    mesh::{Indices, Mesh},
+    pipeline::PrimitiveTopology,
+};
+use std::f32::consts::PI;
+
+/// A sphere made of sectors and stacks
+#[allow(clippy::upper_case_acronyms)]
+#[derive(Debug, Clone, Copy)]
+pub struct UVSphere {
+    /// The radius of the sphere.
+    pub radius: f32,
+    /// Longitudinal sectors
+    pub sectors: usize,
+    /// Latitudinal stacks
+    pub stacks: usize,
+}
+
+impl Default for UVSphere {
+    fn default() -> Self {
+        Self {
+            radius: 1.0,
+            sectors: 36,
+            stacks: 18,
+        }
+    }
+}
+
+impl From<UVSphere> for Mesh {
+    fn from(sphere: UVSphere) -> Self {
+        // Largely inspired from http://www.songho.ca/opengl/gl_sphere.html
+
+        let sectors = sphere.sectors as f32;
+        let stacks = sphere.stacks as f32;
+        let length_inv = 1. / sphere.radius;
+        let sector_step = 2. * PI / sectors;
+        let stack_step = PI / stacks;
+
+        let mut vertices: Vec<[f32; 3]> = Vec::with_capacity(sphere.stacks * sphere.sectors);
+        let mut normals: Vec<[f32; 3]> = Vec::with_capacity(sphere.stacks * sphere.sectors);
+        let mut uvs: Vec<[f32; 2]> = Vec::with_capacity(sphere.stacks * sphere.sectors);
+        let mut indices: Vec<u32> = Vec::with_capacity(sphere.stacks * sphere.sectors * 2 * 3);
+
+        for i in 0..sphere.stacks + 1 {
+            let stack_angle = PI / 2. - (i as f32) * stack_step;
+            let xy = sphere.radius * stack_angle.cos();
+            let z = sphere.radius * stack_angle.sin();
+
+            for j in 0..sphere.sectors + 1 {
+                let sector_angle = (j as f32) * sector_step;
+                let x = xy * sector_angle.cos();
+                let y = xy * sector_angle.sin();
+
+                vertices.push([x, y, z]);
+                normals.push([x * length_inv, y * length_inv, z * length_inv]);
+                uvs.push([(j as f32) / sectors, (i as f32) / stacks]);
+            }
+        }
+
+        // indices
+        //  k1--k1+1
+        //  |  / |
+        //  | /  |
+        //  k2--k2+1
+        for i in 0..sphere.stacks {
+            let mut k1 = i * (sphere.sectors + 1);
+            let mut k2 = k1 + sphere.sectors + 1;
+            for _j in 0..sphere.sectors {
+                if i != 0 {
+                    indices.push(k1 as u32);
+                    indices.push(k2 as u32);
+                    indices.push((k1 + 1) as u32);
+                }
+                if i != sphere.stacks - 1 {
+                    indices.push((k1 + 1) as u32);
+                    indices.push(k2 as u32);
+                    indices.push((k2 + 1) as u32);
+                }
+                k1 += 1;
+                k2 += 1;
+            }
+        }
+
+        let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
+        mesh.set_indices(Some(Indices::U32(indices)));
+        mesh.set_attribute(Mesh::ATTRIBUTE_POSITION, vertices);
+        mesh.set_attribute(Mesh::ATTRIBUTE_NORMAL, normals);
+        mesh.set_attribute(Mesh::ATTRIBUTE_UV_0, uvs);
+        mesh
+    }
+}