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94 lines
3.0 KiB
C++
94 lines
3.0 KiB
C++
/*
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Minetest
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Copyright (C) 2013 celeron55, Perttu Ahola <celeron55@gmail.com>
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License along
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with this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include "light.h"
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#include <algorithm>
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#include <cmath>
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#include "util/numeric.h"
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#include "settings.h"
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#ifndef SERVER
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static u8 light_LUT[LIGHT_SUN + 1];
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// The const ref to light_LUT is what is actually used in the code
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const u8 *light_decode_table = light_LUT;
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struct LightingParams {
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float a, b, c; // Lighting curve polynomial coefficients
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float boost, center, sigma; // Lighting curve parametric boost
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float gamma; // Lighting curve gamma correction
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};
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static LightingParams params;
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float decode_light_f(float x)
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{
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if (x >= 1.0f) // x is often 1.0f
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return 1.0f;
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x = std::fmax(x, 0.0f);
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float brightness = ((params.a * x + params.b) * x + params.c) * x;
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brightness += params.boost *
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std::exp(-0.5f * sqr((x - params.center) / params.sigma));
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if (brightness <= 0.0f) // May happen if parameters are extreme
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return 0.0f;
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if (brightness >= 1.0f)
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return 1.0f;
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return powf(brightness, 1.0f / params.gamma);
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}
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// Initialize or update the light value tables using the specified gamma
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void set_light_table(float gamma)
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{
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// Lighting curve bounding gradients
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const float alpha = rangelim(g_settings->getFloat("lighting_alpha"), 0.0f, 3.0f);
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const float beta = rangelim(g_settings->getFloat("lighting_beta"), 0.0f, 3.0f);
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// Lighting curve polynomial coefficients
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params.a = alpha + beta - 2.0f;
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params.b = 3.0f - 2.0f * alpha - beta;
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params.c = alpha;
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// Lighting curve parametric boost
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params.boost = rangelim(g_settings->getFloat("lighting_boost"), 0.0f, 0.4f);
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params.center = rangelim(g_settings->getFloat("lighting_boost_center"), 0.0f, 1.0f);
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params.sigma = rangelim(g_settings->getFloat("lighting_boost_spread"), 0.0f, 0.4f);
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// Lighting curve gamma correction
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params.gamma = rangelim(gamma, 0.33f, 3.0f);
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// Boundary values should be fixed
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light_LUT[0] = 0;
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light_LUT[LIGHT_SUN] = 255;
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for (size_t i = 1; i < LIGHT_SUN; i++) {
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float brightness = decode_light_f((float)i / LIGHT_SUN);
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// Strictly speaking, rangelim is not necessary here—if the implementation
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// is conforming. But we don’t want problems in any case.
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light_LUT[i] = rangelim((s32)(255.0f * brightness), 0, 255);
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// Ensure light brightens with each level
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if (i > 0 && light_LUT[i] <= light_LUT[i - 1]) {
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light_LUT[i] = std::min((u8)254, light_LUT[i - 1]) + 1;
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}
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}
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}
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#endif
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