Add ACES colorspace conversion and luminance functions. Closes #13

src/ecs/systems/astronomy-system.cpp

@@ -24,6 +24,7 @@
 #include "ecs/components/transform-component.hpp"
 #include "renderer/passes/sky-pass.hpp"
 #include "astro/blackbody.hpp"
+#include "utility/aces.hpp"
 #include <iostream>
 
 namespace ecs {
@@ -88,7 +89,7 @@ void astronomy_system::update(double t, double dt)
 			
 			// Set sun color
 			float correlated_temperature = 3000.0f + std::sin(spherical.y) * 5000.0f;
-			float3 correlated_color = math::type_cast<float>(astro::blackbody(correlated_temperature));
+			float3 correlated_color = math::type_cast<float>(srgb_to_acescg(astro::blackbody(correlated_temperature)));
 			sun_light->set_color(correlated_color);
 
 			// Set sun intensity (in lux)

src/renderer/passes/sky-pass.cpp

@@ -37,6 +37,7 @@
 #include "renderer/material.hpp"
 #include "scene/camera.hpp"
 #include "utility/fundamental-types.hpp"
+#include "utility/aces.hpp"
 #include "math/interpolation.hpp"
 #include "astro/astro.hpp"
 #include <cmath>
@@ -116,9 +117,12 @@ sky_pass::sky_pass(gl::rasterizer* rasterizer, const gl::framebuffer* framebuffe
 		// Calculate linear sRGB color from color temperature
 		double3 color_srgb = astro::blackbody(color_temperature);
 		
+		// Transform to ACEScg colorspace
+		double3 color_acescg = srgb_to_acescg(color_srgb);
+		
 		// Scale color by apparent magnitude
 		double intensity = astro::vmag_to_lux(vmag);
-		double3 scaled_color = color_srgb * intensity;
+		double3 scaled_color = color_acescg * intensity;
 		
 		// Build vertex
 		*(star_vertex++) = static_cast<float>(rectangular.x);
@@ -153,6 +157,10 @@ sky_pass::sky_pass(gl::rasterizer* rasterizer, const gl::framebuffer* framebuffe
 	star_projection_input = star_shader_program->get_input("projection");
 	star_distance_input = star_shader_program->get_input("star_distance");
 	star_exposure_input = star_shader_program->get_input("camera.exposure");
+	
+	std::cout << "vmag_to_lux(-14.2) = " << astro::vmag_to_lux(-14.2) << std::endl;
+	std::cout << "vmag_to_lux(-26.74) = " << astro::vmag_to_lux(-26.74) << std::endl;
+	std::cout << "vmag_to_lux(-1.47) = " << astro::vmag_to_lux(-1.47) << std::endl;
 }
 
 sky_pass::~sky_pass()

src/utility/aces.hpp

@@ -0,0 +1,80 @@
+/*
+ * 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_ACES_HPP
+#define ANTKEEPER_ACES_HPP
+
+#include "math/vector-type.hpp"
+
+/**
+ * Transforms a linear sRGB color into the ACEScg colorspace, using the Bradford chromatic adaption transform.
+ *
+ * @param x Linear sRGB color.
+ * @return Linear ACEScg color.
+ *
+ * @see https://www.colour-science.org/apps/
+ */
+template <class T>
+math::vector<T, 3> srgb_to_acescg(const math::vector<T, 3>& x)
+{
+	static const math::matrix<T, 3, 3> matrix
+	{{
+		{0.6131324224, 0.0701243808, 0.0205876575},
+		{0.3395380158, 0.9163940113, 0.1095745716},
+		{0.0474166960, 0.0134515240, 0.8697854040}
+	}};
+	
+	return matrix * x;
+}
+
+/**
+ * Transforms an ACEScg color into the linear sRGB colorspace, using the Bradford chromatic adaption transform.
+ *
+ * @param x Linear ACEScg color.
+ * @param return Linear sRGB color.
+ *
+ * @see https://www.colour-science.org/apps/
+ */
+template <class T>
+math::vector<T, 3> acescg_to_srgb(const math::vector<T, 3>& x)
+{
+	static const math::matrix<T, 3, 3> matrix
+	{{
+		{ 1.7048586763, -0.1300768242, -0.0239640729},
+		{-0.6217160219,  1.1407357748, -0.1289755083},
+		{-0.0832993717, -0.0105598017,  1.1530140189}
+	}};
+	
+	return matrix * x;
+}
+
+/**
+ * Calculates the luminance of an ACEScg color.
+ *
+ * @param x Linear ACEScg color.
+ * @param return Luminance of @p x.
+ */
+template <class T>
+T acescg_to_luminance(const math::vector<T, 3>& x)
+{
+	static const math::vector<T, 3> luma = {0.2722287168, 0.6740817658, 0.0536895174};
+	return math::dot(x, luma);
+}
+
+#endif // ANTKEEPER_ACES_HPP