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Improve light curve parameter limits and documentation (#9054)

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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.
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Paramat 2019-10-24 01:08:49 +01:00 • committed by GitHub
parent cd35949cd0
commit 1f142ec06f
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2 changed files with 41 additions and 28 deletions
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36
src/light.cpp
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@ -29,44 +29,48 @@ 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; // polynomial coefficients
float boost, center, sigma; // normal boost parameters
float gamma;
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 equal to 1.0f half the time
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 insane
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 derivatives
const float alpha = g_settings->getFloat("lighting_alpha");
const float beta = g_settings->getFloat("lighting_beta");
// Lighting curve coefficients
// 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;
// Mid boost
params.boost = g_settings->getFloat("lighting_boost");
params.center = g_settings->getFloat("lighting_boost_center");
params.sigma = g_settings->getFloat("lighting_boost_spread");
// Gamma correction
params.gamma = rangelim(gamma, 0.5f, 10.0f);
// 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;