From 76c56e16f941e9b0b88e9f8eae6f6941d58d4bb7 Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Wed, 17 Aug 2022 15:24:20 -0700
Subject: [PATCH] Add some (commented out) experiments with Halton.

Halton has less correlation artifacts than Sobol for DoF, but
converges slower.
---
 src/renderer.rs | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/src/renderer.rs b/src/renderer.rs
index 5123670..d383c42 100644
--- a/src/renderer.rs
+++ b/src/renderer.rs
@@ -243,6 +243,12 @@ impl<'a> Renderer<'a> {
                         let d0 = golden_ratio_sample(
                             sii.wrapping_add(rrand::mix32_seed(self.seed, 1111)),
                         );
+
+                        // let siii = crate::scramble::owen2(sii, rrand::mix32_seed(self.seed, 2222));
+                        // let d1 = halton_2(siii, rrand::mix32_seed(self.seed, 3333));
+                        // let d2 = halton_3(siii, rrand::mix32_seed(self.seed, 4444));
+                        // let d3 = halton_5(siii, rrand::mix32_seed(self.seed, 5555));
+
                         let [d1, d2, d3, _] = sample_gen.next_dims_no_owen();
                         sample_gen.inc_padding();
                         let [d4, d5, _, _] = sample_gen.next_dims();
@@ -609,6 +615,41 @@ fn golden_ratio_sample(i: u32) -> f32 {
     u32_to_f32_norm(i.wrapping_mul(2654435769))
 }
 
+// fn halton_2(i: u32, offset: u32) -> f32 {
+//     sobol_burley::parts::u32_to_f32_norm(
+//         i.reverse_bits().wrapping_add(offset)
+//     )
+// }
+
+// fn halton_3(mut i: u32, offset: u32) -> f32 {
+//     const BASE: u32 = 3;
+//     const MAX: u32 = 3486784401;
+//     let mut result = 0;
+//     for _ in 0..20 {
+//         let next = i / BASE;
+//         result *= BASE;
+//         result += i - (next * BASE);
+//         i = next;
+//     }
+
+//     ((result as u64 + offset as u64) % MAX as u64) as f32 * (1.0 / MAX as f32)
+// }
+
+// fn halton_5(mut i: u32, offset: u32) -> f32 {
+//     const BASE: u32 = 5;
+//     const MAX: u32 = 1220703125;
+//     const ORDER: [u32; 5] = [0, 3, 1, 4, 2];
+//     let mut result = 0;
+//     for _ in 0..13 {
+//         let next = i / BASE;
+//         result *= BASE;
+//         result += ORDER[(i - (next * BASE)) as usize];
+//         i = next;
+//     }
+
+//     ((result as u64 + offset as u64) % MAX as u64) as f32 * (1.0 / MAX as f32)
+// }
+
 #[derive(Debug)]
 struct BucketJob {
     x: u32,