From 1709336062b2e941a054dd27bec8872459a70171 Mon Sep 17 00:00:00 2001
From: Bradlee Speice <bradlee@speice.io>
Date: Sat, 20 Jun 2026 10:05:04 -0400
Subject: [PATCH] Add an initial implementation of the chaos game

---
 Cargo.lock               | 17 +++++++++++++++
 Cargo.toml               |  3 ++-
 enkou-shaders/Cargo.toml |  5 +++--
 enkou-shaders/src/lib.rs | 46 +++++++++++++++++++++++++++++++++++++++-
 4 files changed, 67 insertions(+), 4 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index cb8c6b3..4684777 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -155,6 +155,7 @@ version = "0.1.0"
 dependencies = [
  "bytemuck",
  "glam",
+ "rand",
  "spirv-std",
 ]
 
@@ -210,6 +211,7 @@ version = "0.33.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "898f5a568a84989b6c0f8caa50a93074b97dbdc58fc6d9543157bb4562758933"
 dependencies = [
+ "bytemuck",
  "libm",
 ]
 
@@ -435,6 +437,21 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "rand"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d2e8e8bcc7961af1fdac401278c6a831614941f6164ee3bf4ce61b7edb162207"
+dependencies = [
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "63b8176103e19a2643978565ca18b50549f6101881c443590420e4dc998a3c69"
+
 [[package]]
 name = "raw-string"
 version = "0.3.5"
diff --git a/Cargo.toml b/Cargo.toml
index fa17411..cdedf41 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -21,6 +21,7 @@ spirv-std = { git = "https://github.com/Rust-GPU/rust-gpu.git", rev = "67f1ff2"
 
 anyhow = "1.0.102"
 bytemuck = { version = "1.25.0", features = ["derive"] }
-glam = { version = "0.33.1", default-features = false, features = ["libm"] }
+glam = { version = "0.33.1", default-features = false, features = ["bytemuck", "scalar-math"] }
+rand = { version = "0.10.1", default-features = false }
 rspirv = "0.13.0"
 
diff --git a/enkou-shaders/Cargo.toml b/enkou-shaders/Cargo.toml
index 59ffd5a..ecbf4a0 100644
--- a/enkou-shaders/Cargo.toml
+++ b/enkou-shaders/Cargo.toml
@@ -10,6 +10,7 @@ repository.workspace = true
 workspace = true
 
 [dependencies]
-spirv-std.workspace = true
-glam.workspace = true
 bytemuck.workspace = true
+glam.workspace = true
+rand.workspace = true
+spirv-std.workspace = true
diff --git a/enkou-shaders/src/lib.rs b/enkou-shaders/src/lib.rs
index cfadb05..ce89c67 100644
--- a/enkou-shaders/src/lib.rs
+++ b/enkou-shaders/src/lib.rs
@@ -1,8 +1,12 @@
+//! # Enkou
 #![no_std]
+#![warn(missing_docs)]
 
 use bytemuck::{Pod, Zeroable};
 use core::f32::consts::PI;
-use glam::{Affine2, Vec3, Vec4, vec2, vec3};
+use glam::{Affine2, Vec3, Vec4, vec2, vec3, Vec2};
+use rand::{Rng, RngExt};
+use rand::distr::StandardUniform;
 #[cfg(target_arch = "spirv")]
 use spirv_std::num_traits::Float;
 use spirv_std::spirv;
@@ -69,6 +73,46 @@ impl Coefficients2 for Affine2 {
     }
 }
 
+#[derive(Copy, Clone, Pod, Zeroable)]
+#[repr(C)]
+pub struct Transform {
+    pub coefficients: Affine2,
+}
+
+impl Transform {
+    pub fn new(coefficients: Affine2) -> Self {
+        Transform { coefficients }
+    }
+
+    pub fn transform_point(&self, point: Vec2) -> Vec2 {
+        self.coefficients.transform_point2(point)
+    }
+}
+
+/// Iterate one step in the chaos game; choose the next transform, apply it,
+/// and return the resulting point. Also returns the transform index so that
+/// path-dependent weights (the "Xaos" table in Apophysis) can be chosen
+/// for the next iteration step.
+///
+/// # Arguments
+///
+/// * `weights` - Weights are assumed to be normalized; adding all elements together should return the value 1
+pub fn step_chaos_game<R: Rng>(rng: &mut R, point: Vec2, weights: &[f32], transforms: &[Transform]) -> (Vec2, u32) {
+    let mut choice_weight = rng.sample::<f32, _>(StandardUniform);
+    let mut transform_index: u32 = 0;
+
+    for weight in weights {
+        choice_weight -= weight;
+        if choice_weight <= 0.0 {
+            break;
+        }
+
+        transform_index += 1;
+    }
+
+    (transforms[transform_index as usize].transform_point(point), transform_index)
+}
+
 #[derive(Copy, Clone, Pod, Zeroable)]
 #[repr(C)]
 pub struct ShaderConstants {