Attempt to filter away occulted stars.

- does not work properly: tessellated Moon sphere is often smaller than its computed radius!

Author: gzotti

src/core/modules/StarMgr.cpp

@@ -47,6 +47,7 @@
 #include "ConstellationMgr.hpp"
 #include "Planet.hpp"
 #include "StelUtils.hpp"
+#include "SolarSystem.hpp"
 
 #include <QTextStream>
 #include <QFile>
@@ -1271,6 +1272,20 @@ void StarMgr::draw(StelCore* core)
 
 	// Prepare a table for storing precomputed RCMag for all ZoneArrays
 	RCMag rcmag_table[RCMAG_TABLE_SIZE];
+
+	// Try to filter away stars hidden by the Moon!
+	bool filterMoon=false;
+	PlanetP moon = GETSTELMODULE(SolarSystem)->getMoon();
+	Vec3d moonPos=moon->getJ2000EquatorialPos(core);
+	const double moonRadius = moon->getEquatorialRadius() * moon->getSphereScale();
+	double angularSize = atan2(moonRadius, moonPos.length());
+	moonPos.normalize();
+	SphericalCap moonCap(moonPos, cos(angularSize));
+	for (auto  cap : viewportCaps)
+	{
+	    if (cap.intersects(moonCap))
+		filterMoon=true;
+	}
 
 	// Draw all the stars of all the selected zones
 	for (const auto* z : gridLevels)
@@ -1314,9 +1329,9 @@ void StarMgr::draw(StelCore* core)
 		int zone;
 
 		for (GeodesicSearchInsideIterator it1(*geodesic_search_result,z->level);(zone = it1.next()) >= 0;)
-			z->draw(&sPainter, zone, true, rcmag_table, limitMagIndex, core, maxMagStarName, names_brightness, flagDesignations, viewportCaps, withAberration, velf);
+			z->draw(&sPainter, zone, true, rcmag_table, limitMagIndex, core, maxMagStarName, names_brightness, flagDesignations, viewportCaps, withAberration, velf, filterMoon, moonCap);
 		for (GeodesicSearchBorderIterator it1(*geodesic_search_result,z->level);(zone = it1.next()) >= 0;)
-			z->draw(&sPainter, zone, false, rcmag_table, limitMagIndex, core, maxMagStarName,names_brightness, flagDesignations, viewportCaps, withAberration, velf);
+			z->draw(&sPainter, zone, false, rcmag_table, limitMagIndex, core, maxMagStarName,names_brightness, flagDesignations, viewportCaps, withAberration, velf, filterMoon, moonCap);
 	}
 	exit_loop:
 

src/core/modules/ZoneArray.cpp

@@ -412,7 +412,8 @@ template<class Star>
 void SpecialZoneArray<Star>::draw(StelPainter* sPainter, int index, bool isInsideViewport, const RCMag* rcmag_table,
 				  int limitMagIndex, StelCore* core, int maxMagStarName, float names_brightness, bool designationUsage,
 				  const QVector<SphericalCap> &boundingCaps,
-				  const bool withAberration, const Vec3f vel) const
+				  const bool withAberration, const Vec3f vel,
+				  const bool filterMoon, SphericalCap moonCap) const
 {
 	StelSkyDrawer* drawer = core->getSkyDrawer();
 	Vec3f vf;
@@ -478,6 +479,14 @@ void SpecialZoneArray<Star>::draw(StelPainter* sPainter, int index, bool isInsid
 				continue;
 		}
 
+		// If the star is covered by the Moon, don't draw (avoid displaying part of halo of occulted star!)
+		// TODO: This is a bad test. We should draw the moon into a stencil buffer and check that.
+		if (filterMoon)
+		{
+			if (moonCap.contains(vf))
+				continue;
+		}
+
 		int extinctedMagIndex = s->getMag();
 		float twinkleFactor=1.0f; // allow height-dependent twinkle.
 		if (withExtinction)

src/core/modules/ZoneArray.hpp

@@ -103,7 +103,8 @@ class ZoneArray
 					  const RCMag* rcmag_table, int limitMagIndex, StelCore* core,
 					  int maxMagStarName, float names_brightness, bool designationUsage,
 					  const QVector<SphericalCap>& boundingCaps,
-					  const bool withAberration, const Vec3f vel) const = 0;
+					  const bool withAberration, const Vec3f vel,
+					  const bool filterMoon, SphericalCap moonCap) const = 0;
 
 	//! Get whether or not the catalog was successfully loaded.
 	//! @return @c true if at least one zone was loaded, otherwise @c false
@@ -188,7 +189,8 @@ class SpecialZoneArray : public ZoneArray
 			  const RCMag *rcmag_table, int limitMagIndex, StelCore* core,
 			  int maxMagStarName, float names_brightness, bool designationUsage,
 			  const QVector<SphericalCap>& boundingCaps,
-			  const bool withAberration, const Vec3f vel) const Q_DECL_OVERRIDE;
+			  const bool withAberration, const Vec3f vel,
+			  const bool filterMoon, SphericalCap moonCap) const Q_DECL_OVERRIDE;
 
 	virtual void scaleAxis() Q_DECL_OVERRIDE;
 	virtual void searchAround(const StelCore* core, int index,const Vec3d &v,double cosLimFov,