Add more color-related functions, deconstruct blackbody function into separate color functions, move B-V color index function to color index namespace

CMakeLists.txt

@@ -4,6 +4,7 @@ option(VERSION_STRING "Project version string" "0.0.0")
 
 project(antkeeper VERSION ${VERSION_STRING} LANGUAGES CXX)
 
+
 # Find dependency packages
 find_package(dr_wav REQUIRED CONFIG)
 find_package(stb REQUIRED CONFIG)

src/astro/astro.hpp

@@ -24,9 +24,7 @@
 namespace astro {}
 
 #include "apparent-size.hpp"
-#include "blackbody.hpp"
 #include "coordinates.hpp"
-#include "color-index.hpp"
 #include "constants.hpp"
 #include "coordinates.hpp"
 #include "illuminance.hpp"

src/astro/blackbody.cpp

@@ -1,54 +0,0 @@
-/*
- * Copyright (C) 2021  Christopher J. Howard
- *
- * This file is part of Antkeeper source code.
- *
- * Antkeeper source code is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Antkeeper source code is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#include "blackbody.hpp"
-#include <algorithm>
-
-namespace astro
-{
-
-/// Transforms colors from CIE XYZ to linear RGB
-static constexpr double3x3 xyz_to_rgb =
-{
-	3.2404542, -0.9692660, 0.0556434,
-	-1.5371385, 1.8760108, -0.2040259,
-	-0.4985314, 0.0415560, 1.0572252
-};
-
-double3 blackbody(double t)
-{
-	// Approximate the Planckian locus in CIE 1960 UCS color space (Krystek's algorithm)
-	double tt = t * t;
-    double u = (0.860117757 + 1.54118254e-4 * t + 1.28641212e-7 * tt) / (1.0 + 8.42420235e-4 * t + 7.08145163e-7 * tt);
-    double v = (0.317398726 + 4.22806245e-5 * t + 4.20481691e-8 * tt) / (1.0 - 2.89741816e-5 * t + 1.61456053e-7 * tt);
-	
-	// CIE 1960 UCS -> CIE xyY, Y = 1
-    double2 xyy = double2{3.0 * u, 2.0 * v} / (2.0 * u - 8.0 * v + 4.0);
-	
-	// CIE xyY -> CIE XYZ
-	double3 xyz = {xyy.x / xyy.y, 1.0, (1.0 - xyy.x - xyy.y) / xyy.y};
-    
-	// CIE XYZ -> linear RGB
-    double3 rgb = xyz_to_rgb * xyz;
-    
-    // Normalize RGB to preserve chromaticity
-	return rgb / std::max<double>(rgb.x, std::max<double>(rgb.y, rgb.z));
-}
-
-} // namespace astro

src/astro/blackbody.hpp

@@ -1,42 +0,0 @@
-/*
- * Copyright (C) 2021  Christopher J. Howard
- *
- * This file is part of Antkeeper source code.
- *
- * Antkeeper source code is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Antkeeper source code is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#ifndef ANTKEEPER_ASTRO_BLACKBODY_HPP
-#define ANTKEEPER_ASTRO_BLACKBODY_HPP
-
-#include "utility/fundamental-types.hpp"
-
-namespace astro
-{
-
-/**
- * Calculates the color of an ideal black-body radiator, given its temperature in Kelvin.
- *
- * @param t Temperature, in Kelvin.
- * @return Correlated color, in linear sRGB.
- *
- * @see https://en.wikipedia.org/wiki/Planckian_locus
- * @see https://en.wikipedia.org/wiki/CIE_1960_color_space
- * @see https://google.github.io/filament/Filament.html
- */
-double3 blackbody(double t);
-
-} // namespace astro
-
-#endif // ANTKEEPER_ASTRO_BLACKBODY_HPP

src/astro/color-index.cpp

@@ -1,30 +0,0 @@
-/*
- * Copyright (C) 2021  Christopher J. Howard
- *
- * This file is part of Antkeeper source code.
- *
- * Antkeeper source code is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * Antkeeper source code is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#include "color-index.hpp"
-
-namespace astro
-{
-
-double bv_to_k(double bv)
-{
-	return 4600.0 * (1.0 / (0.92 * bv + 1.7) + 1.0 / (0.92 * bv + 0.62));
-}
-
-} // namespace astro

src/color/acescg.hpp

@@ -27,6 +27,10 @@ namespace color {
 /// Functions which operate in the ACEScg colorspace.
 namespace acescg {
 
+/// CIE chromaticity coordinates of the ACEScg white point (~D60).
+template <class T>
+constexpr math::vector2<T> whitepoint = {0.32168, 0.33767};
+
 /**
  * Calculates the luminance of an ACEScg color.
  *

src/color/cct.hpp

@@ -0,0 +1,88 @@
+/*
+ * Copyright (C) 2021  Christopher J. Howard
+ *
+ * This file is part of Antkeeper source code.
+ *
+ * Antkeeper source code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Antkeeper source code is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef ANTKEEPER_COLOR_CCT_HPP
+#define ANTKEEPER_COLOR_CCT_HPP
+
+#include "math/math.hpp"
+#include "ucs.hpp"
+#include "xyy.hpp"
+
+namespace color {
+
+/// Functions which operate on correlated color temperature (CCT).
+namespace cct {
+
+/**
+ * Calculates CIE 1960 UCS colorspace chromaticity coordinates given a correlated color temperature using Krystek's algorithm.
+ *
+ * @param t Correlated color temperature, in Kelvin.
+ * @return CIE 1960 UCS colorspace chromaticity coordinates.
+ *
+ * @see Krystek, M. (1985), An algorithm to calculate correlated colour temperature. Color Res. Appl., 10: 38-40.
+ */
+template <class T>
+math::vector2<T> to_ucs(T t);
+
+/**
+ * Calculates CIE xyY colorspace chromaticity coordinates given a correlated color temperature using Krystek's algorithm.
+ *
+ * @param t Correlated color temperature, in Kelvin.
+ * @return CIE xyY color with `Y = 1`.
+ */
+template <class T>
+math::vector3<T> to_xyy(T t);
+
+/**
+ * Calculates CIE XYZ colorspace chromaticity coordinates given a correlated color temperature using Krystek's algorithm.
+ *
+ * @param t Correlated color temperature, in Kelvin.
+ * @return CIE XYZ color with `Y = 1`.
+ */
+template <class T>
+math::vector3<T> to_xyz(T t);
+
+template <class T>
+math::vector2<T> to_ucs(T t)
+{
+	// Approximate the Planckian locus in CIE 1960 UCS colorspace (Krystek's algorithm)
+	const T tt = t * t;
+	return math::vector2<T>
+		{
+			(T(0.860117757) + T(1.54118254e-4) * t + T(1.28641212e-7) * tt) / (T(1.0) + T(8.42420235e-4) * t + T(7.08145163e-7) * tt),
+			(T(0.317398726) + T(4.22806245e-5) * t + T(4.20481691e-8) * tt) / (T(1.0) - T(2.89741816e-5) * t + T(1.61456053e-7) * tt)
+		};
+}
+
+template <class T>
+math::vector3<T> to_xyy(T t)
+{
+	return ucs::to_xyy(to_ucs(t), T(1.0));
+}
+
+template <class T>
+math::vector3<T> to_xyz(T t)
+{
+	return xyy::to_xyz(to_xyy(t));
+}
+
+} // namespace cct
+} // namespace color
+
+#endif // ANTKEEPER_COLOR_CCT_HPP

src/color/color.hpp

@@ -24,7 +24,11 @@
 namespace color {}
 
 #include "acescg.hpp"
+#include "cct.hpp"
+#include "index.hpp"
 #include "srgb.hpp"
+#include "ucs.hpp"
+#include "xyy.hpp"
 #include "xyz.hpp"
 
 #endif // ANTKEEPER_COLOR_HPP

src/astro/color-index.hpp → src/color/index.hpp

@@ -17,22 +17,32 @@
  * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef ANTKEEPER_ASTRO_COLOR_INDEX_HPP
-#define ANTKEEPER_ASTRO_COLOR_INDEX_HPP
+#ifndef ANTKEEPER_COLOR_INDEX_HPP
+#define ANTKEEPER_COLOR_INDEX_HPP
 
-namespace astro
-{
+namespace color {
+
+/// Functions which operate on color indices.
+namespace index {
 
 /**
  * Approximates the temperature of a star, given its B-V index.
  *
  * @param bv B-V index.
- * @return Temperature, in Kelvin.
+ * @return Correlated color temperature, in Kelvin.
  *
  * @see Ballesteros, F. J. (2012). "New insights into black bodies". EPL 97 (2012) 34008.
  */
-double bv_to_k(double bv);
+template <class T>
+T bv_to_cct(T bv);
+
+template <class T>
+T bv_to_cct(T bv)
+{
+	return T(4600.0) * (T(1.0) / (T(0.92) * bv + T(1.7)) + T(1.0) / (T(0.92) * bv + T(0.62)));
+}
 
-} // namespace astro
+} // namespace index
+} // namespace color
 
-#endif // ANTKEEPER_ASTRO_COLOR_INDEX_HPP
+#endif // ANTKEEPER_COLOR_INDEX_HPP

src/color/srgb.hpp

@@ -28,6 +28,10 @@ namespace color {
 /// Functions which operate in the sRGB colorspace.
 namespace srgb {
 
+/// CIE chromaticity coordinates of the sRGB white point (D65)
+template <class T>
+constexpr math::vector2<T> whitepoint = {0.31271, 0.32902};
+
 /**
  * Performs the sRGB Electro-Optical Transfer Function (EOTF), also known as the sRGB decoding function.
  *

src/color/ucs.hpp

@@ -28,24 +28,24 @@ namespace color {
 namespace ucs {
 
 /**
- * Transforms a CIE 1960 UCS color into the CIE xyY colorspace.
+ * Transforms CIE 1960 UCS chromaticity coordinates into the CIE xyY colorspace.
  *
- * @param uv CIE 1960 UCS color coordinates.
+ * @param uv CIE 1960 UCS chromaticity coordinates.
  * @param luminance Luminance or `Y` value of the resulting xyY color.
  * @return CIE xyY color.
  */
 template <class T>
-math::vector3<T> to_xyy(const math::vector2<T>& uv, T luminance);
+math::vector3<T> to_xyy(const math::vector2<T>& uv, T luminance = T(1.0));
 
 template <class T>
-math::vector3<T> to_xyy(const math::vector2<T>& uv, T luminance);
+math::vector3<T> to_xyy(const math::vector2<T>& uv, T luminance)
 {
-	const T inverse_denom = 1.0 / (2.0 * uv[0] - 8.0 * uv[1] + 4.0);
+	const T inverse_denom = T(1.0) / (T(2.0) * uv[0] - T(8.0) * uv[1] + T(4.0));
 	
 	return math::vector3<T>
 		{
-			(3.0 * uv[0]) * inverse_denom,
-			(2.0 * uv[1]) * inverse_denom,
+			(T(3.0) * uv[0]) * inverse_denom,
+			(T(2.0) * uv[1]) * inverse_denom,
 			luminance
 		};
 }

src/color/xyy.hpp

@@ -63,12 +63,12 @@ inline T luminance(const math::vector3& x)
 template <class T>
 math::vector2<T> to_ucs(const math::vector3<T>& x)
 {
-	const T inverse_denom = 1.0 / (-2.0 * x[0] + 12.0 * x[1] + 3.0);
+	const T inverse_denom = T(1.0) / (T(-2.0) * x[0] + T(12.0) * x[1] + T(3.0));
 	
 	return math::vector2<T>
 		{
-			(4.0 * x[0]) * inverse_denom,
-			(6.0 * x[1]) * inverse_denom
+			(T(4.0) * x[0]) * inverse_denom,
+			(T(6.0) * x[1]) * inverse_denom
 		};
 }
 
@@ -79,7 +79,7 @@ math::vector3 to_xyz(const math::vector3& x)
 		{
 			(x[0] * x[2]) / x[1],
 			x[2],
-			((1.0 - x[0] - x[1]) * x[2]) / x[1]
+			((T(1.0) - x[0] - x[1]) * x[2]) / x[1]
 		};
 }
 

src/color/xyz.hpp

@@ -63,6 +63,29 @@ math::vector3 to_srgb(const math::vector3& x);
 template <class T>
 math::vector3<T> to_xyy(const math::vector3<T>& x);
 
+/// Chromatic Adaptation Transforms (CATs).
+namespace cat {
+
+	/**
+	 * Transforms a CIE XYZ color with an ACES (~D60) illuminant to a CIE XYZ color with a D65 illuminant using the Bradford chromatic adaption transform.
+	 *
+	 * @param x CIE XYZ color with an ACES (~D60) illuminant.
+	 * @return CIE XYZ color with a D65 illuminant.
+	 */
+	template <class T>
+	math::vector3<T> aces_to_d65(const math::vector3<T>& x);
+
+	/**
+	 * Transforms a CIE XYZ color with a D65 illuminant to a CIE XYZ color with an ACES (~D60) illuminant using the Bradford chromatic adaption transform.
+	 *
+	 * @param x CIE XYZ color with a D65 illuminant.
+	 * @return CIE XYZ color with an ACES (~D60) illuminant.
+	 */
+	template <class T>
+	math::vector3<T> d65_to_aces(const math::vector3<T>& x);
+
+} // namespace cat
+
 template <class T>
 inline T luminance(const math::vector3<T>& x)
 {
@@ -74,9 +97,9 @@ math::vector3 to_acescg(const math::vector3& x)
 {
 	static const math::matrix3<T> xyz_to_acescg
 	{{
-		{ 1.641023379694326 -0.663662858722983  0.011721894328375},
-		{-0.324803294184790  1.615331591657338 -0.008284441996237},
-		{-0.236424695237612, 0.016756347685530, 0.988394858539022}
+		{ 1.641023379694326, -0.663662858722983,  0.011721894328375},
+		{-0.324803294184790,  1.615331591657338, -0.008284441996237},
+		{-0.236424695237612,  0.016756347685530,  0.988394858539022}
 	}};
 	
 	return xyz_to_acescg * x;
@@ -108,6 +131,36 @@ math::vector3 to_xyy(const math::vector3& x)
 		};
 }
 
+namespace cat {
+
+	template <class T>
+	math::vector3<T> aces_to_d65(const math::vector3<T>& x)
+	{
+		static const math::matrix3<T> cat_aces_to_d65
+		{{
+			{ 0.987225397551079, -0.007603864790602,  0.003066041131217},
+			{-0.006114800968213,  1.001874800208719, -0.005084242870792},
+			{ 0.015926393295811,  0.005322023893623,  1.081519155692042}
+		}};
+		
+		return cat_aces_to_d65 * x;
+	}
+
+	template <class T>
+	math::vector3<T> d65_to_aces(const math::vector3<T>& x)
+	{
+		static const math::matrix3<T> cat_d65_to_aces
+		{{
+			{ 1.013033366661459,  0.007703617525351, -0.002835673220262},
+			{ 0.006107049021859,  0.998150224406968,  0.004675010768250},
+			{-0.014947927269674, -0.005025218608126,  0.924644077051100}
+		}};
+		
+		return cat_d65_to_aces * x;
+	}
+
+} // namespace cat
+
 } // namespace xyz
 } // namespace color
 

src/ecs/systems/astronomy-system.cpp

@@ -23,7 +23,6 @@
 #include "ecs/components/celestial-body-component.hpp"
 #include "ecs/components/transform-component.hpp"
 #include "renderer/passes/sky-pass.hpp"
-#include "astro/blackbody.hpp"
 #include "color/color.hpp"
 #include <iostream>
 
@@ -88,9 +87,11 @@ void astronomy_system::update(double t, double dt)
 			//sun_light->look_at({0, 0, 0}, {0, -1, 0}, {0, 0, 1});
 			
 			// Set sun color
-			float correlated_temperature = 3000.0f + std::sin(spherical.y) * 5000.0f;
-			float3 correlated_color = math::type_cast<float>(color::srgb::to_acescg(astro::blackbody(correlated_temperature)));
-			sun_light->set_color(correlated_color);
+			float cct = 3000.0f + std::sin(spherical.y) * 5000.0f;
+			float3 color_xyz = color::cct::to_xyz(cct);
+			float3 color_acescg = color::xyz::to_acescg(color_xyz);
+			
+			sun_light->set_color(color_acescg);
 
 			// Set sun intensity (in lux)
 			float intensity = std::max(0.0, std::sin(spherical.y) * 108000.0f);

src/game/states/play-state.cpp

@@ -61,7 +61,6 @@
 #include "ecs/systems/astronomy-system.hpp"
 #include "game/biome.hpp"
 #include "utility/fundamental-types.hpp"
-#include "astro/blackbody.hpp"
 
 #include "utility/bit-math.hpp"
 #include "genetics/genetics.hpp"
@@ -146,8 +145,8 @@ void play_state_enter(game_context* ctx)
 	
 	scene::directional_light* sun = new scene::directional_light();
 	
-	float3 sun_color = math::type_cast<float>(astro::blackbody(6000.0)); // NOTE: this is linear sRGB, should be ACEScg
-	sun->set_color(sun_color);
+	//float3 sun_color = math::type_cast<float>(astro::blackbody(6000.0)); // NOTE: this is linear sRGB, should be ACEScg
+	//sun->set_color(sun_color);
 	sun->set_intensity(1000.0f);
 	sun->set_light_texture(resource_manager->load<gl::texture_2d>("forest-gobo.tex"));
 	sun->set_light_texture_scale({2000, 2000});

src/renderer/passes/sky-pass.cpp

@@ -112,22 +112,22 @@ sky_pass::sky_pass(gl::rasterizer* rasterizer, const gl::framebuffer* framebuffe
 		double3 rectangular = astro::spherical_to_rectangular(spherical);
 		
 		// Convert color index to color temperature
-		double color_temperature = astro::bv_to_k(bv_color);
+		double cct = color::index::bv_to_cct(bv_color);
 		
-		// Calculate linear sRGB color from color temperature
-		double3 color_srgb = astro::blackbody(color_temperature);
+		// Calculate XYZ color from color temperature
+		double3 color_xyz = color::cct::to_xyz(cct);
 		
-		// Transform to ACEScg colorspace
-		double3 color_acescg = color::srgb::to_acescg(color_srgb);
+		// Transform XYZ from (assumed) D65 illuminant to ACES illuminant.
+		//color_xyz = color::xyz::cat::d65_to_aces(color_xyz);
 		
-		// Calculate color luminance
-		double color_luminance = color::acescg::luminance(color_acescg);
+		// Transform XYZ color to ACEScg colorspace
+		double3 color_acescg = color::xyz::to_acescg(color_xyz);
 		
 		// Convert apparent magnitude to lux
 		double vmag_lux = astro::vmag_to_lux(vmag);
 		
 		// Normalized color luminance and scale by apparent magnitude
-		double3 scaled_color = color_acescg * ((1.0 / color_luminance) * vmag_lux);
+		double3 scaled_color = color_acescg * vmag_lux;
 		
 		// Build vertex
 		*(star_vertex++) = static_cast<float>(rectangular.x);