add initial support to display variable brightness for variable stars

Author: henrysky

src/core/modules/Star.hpp

@@ -446,6 +446,36 @@ struct Star
       pmdec = sky_orbit_vel.dot(q2) * 1000.;
       StelUtils::rectToSphe(&ra, &dec, v);
    }
+
+   inline void getVarStarOffset(double epoch, double &offset) const // get brightness offset for variable stars (not actual brightness)
+   {
+      StarId star_id;  // star ID
+      if (getGaia() == 0)
+      {
+         star_id = getHip();
+      }
+      else
+      {
+         star_id = getGaia();
+      }
+      double period = StarMgr::getGcvsPeriod(star_id) / 365.25;
+      if (period <=0.)  // not a variable star
+         return;
+      double dyrs = (epoch - STAR_CATALOG_JDEPOCH) / 365.25;
+      double min1mag = StarMgr::getGcvsMinMagnitude(star_id) * 1000.;
+      double maxmag = StarMgr::getGcvsMaxMagnitude(star_id) * 1000.;
+      double epoch_offset = (StarMgr::getGcvsEpoch(star_id) - STAR_CATALOG_JDEPOCH) / 365.25;
+      double phase = fmod(dyrs - epoch_offset, period) / period;
+   
+      if (period && min1mag && maxmag && min1mag > maxmag)
+      {
+         double amplitude = (min1mag - maxmag) / 2.;
+         if (phase < 0.0)
+            phase += 1.0;
+         // sine wave
+         offset = amplitude * sin(2. * M_PI * phase);
+      }
+   }   
 };
 
 struct Star1 : public Star<Star1>

src/core/modules/StarWrapper.cpp

@@ -303,7 +303,9 @@ QString StarWrapper1::getInfoString(const StelCore *core, const InfoStringGroup&
 	{
 		magOffset = 5.f * log10(s->getPlx()/Plx);
 	} 
-	oss << getMagnitudeInfoString(core, flags, 2, magOffset);
+	double variable_magoffset = 0.0;
+	s->getVarStarOffset(core->getJDE(), variable_magoffset);
+	oss << getMagnitudeInfoString(core, flags, 2, magOffset + variable_magoffset / 1000.);
 
 	// should use Plx from getPlx because Plx can change with time, but not absolute magnitude
 	if ((flags&AbsoluteMagnitude) && s->getPlx())
@@ -658,7 +660,9 @@ QString StarWrapper2::getInfoString(const StelCore *core, const InfoStringGroup&
 			oss << QString("%1: <b>%2</b>").arg(q_("Type"), objectTypeI18nStr) << "<br />";
 	}
 
-	oss << getMagnitudeInfoString(core, flags, 2);
+	double variable_magoffset = 0.0;
+	s->getVarStarOffset(core->getJDE(), variable_magoffset);
+	oss << getMagnitudeInfoString(core, flags, 2, variable_magoffset / 1000.);
 
 	double RA, DEC, pmra, pmdec, Plx, RadialVel;
 	double PlxErr = s->getPlxErr();
@@ -884,7 +888,9 @@ QString StarWrapper3::getInfoString(const StelCore *core, const InfoStringGroup&
 			oss << QString("%1: <b>%2</b>").arg(q_("Type"), objectTypeI18nStr) << "<br />";
 	}
 
-	oss << getMagnitudeInfoString(core, flags, 2);
+	double variable_magoffset = 0.0;
+	s->getVarStarOffset(core->getJDE(), variable_magoffset);
+	oss << getMagnitudeInfoString(core, flags, 2, variable_magoffset / 1000.);
 
 	if (flags&Extra)
 	{

src/core/modules/ZoneArray.cpp

@@ -487,6 +487,11 @@ void SpecialZoneArray<Star>::draw(StelPainter* sPainter, int index, bool isInsid
 			Vec3d u = (r * (1. + pmr0 * dyrs) + pmvec0 * dyrs) * f;
 			v.set(u[0], u[1], u[2]);
 		}
+		// take variable star brightness delta into account
+		double variable_magoffset = 0.0;
+		s->getVarStarOffset(core->getJDE(), variable_magoffset);
+		starMag += variable_magoffset;
+
 		// recompute magIndex with the new magnitude
 		magIndex = static_cast<int>((starMag - (mag_min - 7000.)) * 0.02);  // 1 / (50 milli-mag)