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Updated star rendering phases/parameters

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As part of this, adjust the normalisation so the active cutoff value
corresponds to 0.0 normalised intensity.
This commit is contained in:
James Turner
2019-02-25 16:12:30 +00:00
parent 10a701308d
commit 7e969f4e28
1 changed files with 46 additions and 20 deletions
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66
simgear/scene/sky/stars.cxx
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@@ -124,49 +124,77 @@ SGStars::build( int num, const SGVec3d star_data[], double star_dist ) {
// 0 degrees = high noon
// 90 degrees = sun rise/set
// 180 degrees = darkest midnight
bool SGStars::repaint( double sun_angle, int num, const SGVec3d star_data[] ) {
// cout << "repainting stars" << endl;
// double min = 100;
// double max = -100;
bool SGStars::repaint( double sun_angle, int num, const SGVec3d star_data[] )
{
double mag, nmag, alpha, factor, cutoff;
/*
maximal magnitudes under dark sky on Earth, from Eq.(90) and (91) of astro-ph/1405.4209
For (18 < musky < 20)
mmax = 0.27 musky + 0.8 - 2.5 * log(F)
For (19.5 µsky 22)
mmax = 0.383 musky - 1.44 - 2.5 * log(F)
Let's take F = 1.4 for healthy young pilot
mudarksky ~ 22 mag/arcsec^2 => mmax=6.2
muastrotwilight ~ 20 mag/arsec^2 => mmax=5.4
mu99deg ~ 17.5 mag/arcsec^2 => mmax=4.7
mu97.5deg ~ 16 mag/arcsec^2 => ? let's keep it rough
*/
double mag_nakedeye = 6.2;
double mag_twilight_astro = 5.4;
double mag_twilight_nautic = 4.7;
// sirius, brightest star (not brightest object)
double mag_min = -1.46;
int phase;
// determine which star structure to draw
if ( sun_angle > (SGD_PI_2 + 10.0 * SGD_DEGREES_TO_RADIANS ) ) {
// deep night
if ( sun_angle > (SGD_PI_2 + 18.0 * SGD_DEGREES_TO_RADIANS ) ) {
// deep night, atmosphere is not lighten by the sun
factor = 1.0;
cutoff = 4.5;
cutoff = mag_nakedeye;
phase = 0;
} else if ( sun_angle > (SGD_PI_2 + 8.8 * SGD_DEGREES_TO_RADIANS ) ) {
} else if ( sun_angle > (SGD_PI_2 + 12.0 * SGD_DEGREES_TO_RADIANS ) ) {
// less than 18deg and more than 12deg is astronomical twilight
factor = 1.0;
cutoff = 3.8;
cutoff = mag_twilight_astro;
phase = 1;
} else if ( sun_angle > (SGD_PI_2 + 9.0 * SGD_DEGREES_TO_RADIANS ) ) {
// less 12deg and more than 6deg is is nautical twilight
factor = 1.0;
cutoff = mag_twilight_nautic;
phase = 2;
} else if ( sun_angle > (SGD_PI_2 + 7.5 * SGD_DEGREES_TO_RADIANS ) ) {
factor = 0.95;
cutoff = 3.1;
phase = 2;
phase = 3;
} else if ( sun_angle > (SGD_PI_2 + 7.0 * SGD_DEGREES_TO_RADIANS ) ) {
factor = 0.9;
cutoff = 2.4;
phase = 3;
phase = 4;
} else if ( sun_angle > (SGD_PI_2 + 6.5 * SGD_DEGREES_TO_RADIANS ) ) {
factor = 0.85;
cutoff = 1.8;
phase = 4;
phase = 5;
} else if ( sun_angle > (SGD_PI_2 + 6.0 * SGD_DEGREES_TO_RADIANS ) ) {
factor = 0.8;
cutoff = 1.2;
phase = 5;
phase = 6;
} else if ( sun_angle > (SGD_PI_2 + 5.5 * SGD_DEGREES_TO_RADIANS ) ) {
factor = 0.75;
cutoff = 0.6;
phase = 6;
phase = 7;
} else {
// early dusk or late dawn
factor = 0.7;
cutoff = 0.0;
phase = 7;
phase = 8;
}
if (_cutoffProperty) {
@@ -183,17 +211,15 @@ bool SGStars::repaint( double sun_angle, int num, const SGVec3d star_data[] ) {
// if ( star_data[i][2] < min ) { min = star_data[i][2]; }
// if ( star_data[i][2] > max ) { max = star_data[i][2]; }
// magnitude ranges from -1 (bright) to 4 (dim). The
// magnitude ranges from -1 (bright) to 6 (dim). The
// range of star and planet magnitudes can actually go
// outside of this, but for our purpose, if it is brighter
// that -1, we'll color it full white/alpha anyway and 4
// is a convenient cutoff point which keeps the number of
// stars drawn at about 500.
// that magmin, we'll color it full white/alpha anyway
// color (magnitude)
mag = star_data[i][2];
if ( mag < cutoff ) {
nmag = ( 4.5 - mag ) / 5.5; // translate to 0 ... 1.0 scale
nmag = ( cutoff - mag ) / (cutoff - mag_min); // translate to 0 ... 1.0 scale
alpha = nmag * 0.85 + 0.15; // translate to a 0.15 ... 1.0 scale
alpha *= factor; // dim when the sun is brighter
} else {