Minor tidy.

Cargo.lock

@@ -993,6 +993,7 @@ dependencies = [
  "bevy",
  "bevy_mod_debugdump",
  "heron",
+ "rand",
 ]
 
 [[package]]
@@ -1572,9 +1573,9 @@ checksum = "1b03d17f364a3a042d5e5d46b053bbbf82c92c9430c592dd4c064dc6ee997125"
 
 [[package]]
 name = "libloading"
-version = "0.7.2"
+version = "0.7.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "afe203d669ec979b7128619bae5a63b7b42e9203c1b29146079ee05e2f604b52"
+checksum = "efbc0f03f9a775e9f6aed295c6a1ba2253c5757a9e03d55c6caa46a681abcddd"
 dependencies = [
  "cfg-if 1.0.0",
  "winapi",
@@ -2374,9 +2375,9 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.74"
+version = "1.0.75"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ee2bb9cd061c5865d345bb02ca49fcef1391741b672b54a0bf7b679badec3142"
+checksum = "c059c05b48c5c0067d4b4b2b4f0732dd65feb52daf7e0ea09cd87e7dadc1af79"
 dependencies = [
  "itoa",
  "ryu",
@@ -2622,9 +2623,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-subscriber"
-version = "0.3.5"
+version = "0.3.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5d81bfa81424cc98cb034b837c985b7a290f592e5b4322f353f94a0ab0f9f594"
+checksum = "77be66445c4eeebb934a7340f227bfe7b338173d3f8c00a60a5a58005c9faecf"
 dependencies = [
  "ansi_term",
  "lazy_static",

Cargo.toml

@@ -5,6 +5,7 @@ edition = "2021"
 
 [dependencies]
 bevy_mod_debugdump = "0.3.0"
+rand = "0.8.4"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 

src/lib.rs

@@ -1,6 +1,6 @@
 use bevy::{
     ecs::schedule::StageLabel,
-    prelude::{ResMut, SystemLabel, Windows},
+    prelude::{ResMut, SystemLabel, Vec3, Windows},
 };
 
 pub mod action;
@@ -24,3 +24,23 @@ pub fn disable_mouse_trap(mut windows: ResMut<Windows>) {
     window.set_cursor_lock_mode(false);
     window.set_cursor_visibility(true);
 }
+
+pub fn random_sphere_vec(r: &mut impl rand::prelude::Rng) -> Vec3 {
+    // https://mathworld.wolfram.com/SpherePointPicking.html
+    // Marsaglia (1972) for picking x1 and x2 from (-1, 1) and generating surface
+    // points directly if their sum is less than 1.
+
+    let mut x1 = 0.0;
+    let mut x2 = 0.0;
+    let mut ssum = 2.0;
+    while ssum >= 1.0 {
+        x1 = r.gen_range(-1.0..=1.0);
+        x2 = r.gen_range(-1.0..=1.0);
+        ssum = x1.powi(2) + x2.powi(2);
+    }
+    let sqrt = (1.0 - x1.powi(2) - x2.powi(2)).sqrt();
+    let x = 2.0 * x1 * sqrt;
+    let y = 2.0 * x2 * sqrt;
+    let z = 1.0 - 2.0 * ssum;
+    Vec3::new(x, y, z)
+}