Initial commit

src/light.cpp

@@ -0,0 +1,93 @@
+/*
+Minetest
+Copyright (C) 2013 celeron55, Perttu Ahola <celeron55@gmail.com>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program 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 Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#include "light.h"
+#include <algorithm>
+#include <cmath>
+#include "util/numeric.h"
+#include "settings.h"
+
+#ifndef SERVER
+
+static u8 light_LUT[LIGHT_SUN + 1];
+
+// The const ref to light_LUT is what is actually used in the code
+const u8 *light_decode_table = light_LUT;
+
+
+struct LightingParams {
+	float a, b, c; // Lighting curve polynomial coefficients
+	float boost, center, sigma; // Lighting curve parametric boost
+	float gamma; // Lighting curve gamma correction
+};
+
+static LightingParams params;
+
+
+float decode_light_f(float x)
+{
+	if (x >= 1.0f) // x is often 1.0f
+		return 1.0f;
+	x = std::fmax(x, 0.0f);
+	float brightness = ((params.a * x + params.b) * x + params.c) * x;
+	brightness += params.boost *
+		std::exp(-0.5f * sqr((x - params.center) / params.sigma));
+	if (brightness <= 0.0f) // May happen if parameters are extreme
+		return 0.0f;
+	if (brightness >= 1.0f)
+		return 1.0f;
+	return powf(brightness, 1.0f / params.gamma);
+}
+
+
+// Initialize or update the light value tables using the specified gamma
+void set_light_table(float gamma)
+{
+// Lighting curve bounding gradients
+	const float alpha = rangelim(g_settings->getFloat("lighting_alpha"), 0.0f, 3.0f);
+	const float beta  = rangelim(g_settings->getFloat("lighting_beta"), 0.0f, 3.0f);
+// Lighting curve polynomial coefficients
+	params.a = alpha + beta - 2.0f;
+	params.b = 3.0f - 2.0f * alpha - beta;
+	params.c = alpha;
+// Lighting curve parametric boost
+	params.boost = rangelim(g_settings->getFloat("lighting_boost"), 0.0f, 0.4f);
+	params.center = rangelim(g_settings->getFloat("lighting_boost_center"), 0.0f, 1.0f);
+	params.sigma = rangelim(g_settings->getFloat("lighting_boost_spread"), 0.0f, 0.4f);
+// Lighting curve gamma correction
+	params.gamma = rangelim(gamma, 0.33f, 3.0f);
+
+// Boundary values should be fixed
+	light_LUT[0] = 0;
+	light_LUT[LIGHT_SUN] = 255;
+
+	for (size_t i = 1; i < LIGHT_SUN; i++) {
+		float brightness = decode_light_f((float)i / LIGHT_SUN);
+		// Strictly speaking, rangelim is not necessary here—if the implementation
+		// is conforming. But we don’t want problems in any case.
+		light_LUT[i] = rangelim((s32)(255.0f * brightness), 0, 255);
+
+		// Ensure light brightens with each level
+		if (i > 0 && light_LUT[i] <= light_LUT[i - 1]) {
+			light_LUT[i] = std::min((u8)254, light_LUT[i - 1]) + 1;
+		}
+	}
+}
+
+#endif