minetest/src/light.cpp
Paramat 1f142ec06f
Improve light curve parameter limits and documentation (#9054)
Revert gamma upper limit to 3.0 because that was raised based on
a misunderstanding and had no benefit. A sane upper limit is
needed as players on a competitive server tend to use the maximum.
Set gamma lower limit to 0.33 for consistency with 3.0.
Set sane limits on alpha, beta, boost and enforce these in code
to limit values entered in minetest.conf and to avoid easy cheating
by editing settingtypes.txt.
Improve documentation and 'readable' setting names.
Clarify that gamma does not significantly affect natural night light.
light.cpp: Various codestyle and comment improvements.
2019-10-24 01:08:49 +01:00

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/*
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 <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 dont want problems in any case.
light_LUT[i] = rangelim((s32)(255.0f * brightness), 0, 255);
// Ensure light brightens with each level
if (i > 1 && light_LUT[i] <= light_LUT[i - 1])
light_LUT[i] = light_LUT[i - 1] + 1;
}
}
#endif