From 8bc6b240047ec20d89d30f85959fc81119043fb8 Mon Sep 17 00:00:00 2001
From: Nathan Vegdahl <cessen@cessen.com>
Date: Mon, 1 Aug 2022 22:04:14 -0700
Subject: [PATCH] Switch to CIE XYZ lookup tables.

---
 Cargo.lock   |  7 +++++++
 Cargo.toml   |  2 +-
 src/color.rs | 47 ++++++++++++++++++++++++++++++++++++-----------
 3 files changed, 44 insertions(+), 12 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index d8e1ef4..2d9ec2d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -127,6 +127,12 @@ dependencies = [
 name = "color"
 version = "0.1.0"
 
+[[package]]
+name = "colorbox"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d27d55561009760957654f467735e73806f8bc2d081cc4a22e93403ecd156fc"
+
 [[package]]
 name = "compact"
 version = "0.1.0"
@@ -329,6 +335,7 @@ dependencies = [
  "bvh_order",
  "clap",
  "color",
+ "colorbox",
  "compact",
  "copy_in_place",
  "crossbeam",
diff --git a/Cargo.toml b/Cargo.toml
index c9724c5..a97adbf 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -36,7 +36,7 @@ rustc-serialize = "0.3"
 scoped_threadpool = "0.1"
 time = "0.1"
 fastapprox = "0.3"
-
+colorbox = "0.3"
 
 
 # Local crate dependencies
diff --git a/src/color.rs b/src/color.rs
index 9e68b70..e438609 100644
--- a/src/color.rs
+++ b/src/color.rs
@@ -608,21 +608,46 @@ fn xyz_to_spectrum_4(xyz: (f32, f32, f32), wavelengths: Float4) -> Float4 {
 /// From the paper "Simple Analytic Approximations to the CIE XYZ Color Matching
 /// Functions" by Wyman et al.
 pub fn x_1931(wavelength: f32) -> f32 {
-    let t1 = (wavelength - 442.0) * (if wavelength < 442.0 { 0.0624 } else { 0.0374 });
-    let t2 = (wavelength - 599.8) * (if wavelength < 599.8 { 0.0264 } else { 0.0323 });
-    let t3 = (wavelength - 501.1) * (if wavelength < 501.1 { 0.0490 } else { 0.0382 });
-    (0.362 * fast_exp(-0.5 * t1 * t1)) + (1.056 * fast_exp(-0.5 * t2 * t2))
-        - (0.065 * fast_exp(-0.5 * t3 * t3))
+    use colorbox::tables::cie_1931_xyz::{MAX_WAVELENGTH, MIN_WAVELENGTH, X};
+
+    let norm = 1.0 / (MAX_WAVELENGTH - MIN_WAVELENGTH);
+    let n = (wavelength - MIN_WAVELENGTH) * norm;
+
+    if n < 0.0 {
+        X[0]
+    } else if n > 1.0 {
+        *X.last().unwrap()
+    } else {
+        crate::lerp::lerp_slice(X, n)
+    }
 }
 
 pub fn y_1931(wavelength: f32) -> f32 {
-    let t1 = (wavelength - 568.8) * (if wavelength < 568.8 { 0.0213 } else { 0.0247 });
-    let t2 = (wavelength - 530.9) * (if wavelength < 530.9 { 0.0613 } else { 0.0322 });
-    (0.821 * fast_exp(-0.5 * t1 * t1)) + (0.286 * fast_exp(-0.5 * t2 * t2))
+    use colorbox::tables::cie_1931_xyz::{MAX_WAVELENGTH, MIN_WAVELENGTH, Y};
+
+    let norm = 1.0 / (MAX_WAVELENGTH - MIN_WAVELENGTH);
+    let n = (wavelength - MIN_WAVELENGTH) * norm;
+
+    if n < 0.0 {
+        Y[0]
+    } else if n > 1.0 {
+        *Y.last().unwrap()
+    } else {
+        crate::lerp::lerp_slice(Y, n)
+    }
 }
 
 pub fn z_1931(wavelength: f32) -> f32 {
-    let t1 = (wavelength - 437.0) * (if wavelength < 437.0 { 0.0845 } else { 0.0278 });
-    let t2 = (wavelength - 459.0) * (if wavelength < 459.0 { 0.0385 } else { 0.0725 });
-    (1.217 * fast_exp(-0.5 * t1 * t1)) + (0.681 * fast_exp(-0.5 * t2 * t2))
+    use colorbox::tables::cie_1931_xyz::{MAX_WAVELENGTH, MIN_WAVELENGTH, Z};
+
+    let norm = 1.0 / (MAX_WAVELENGTH - MIN_WAVELENGTH);
+    let n = (wavelength - MIN_WAVELENGTH) * norm;
+
+    if n < 0.0 {
+        Z[0]
+    } else if n > 1.0 {
+        *Z.last().unwrap()
+    } else {
+        crate::lerp::lerp_slice(Z, n)
+    }
 }