Merge lp:~stellarium/stellarium/corona into lp:stellarium

[Alexander Wolf]

I tried restore a lost feature - showing the Sun's corona during total solar eclipse.

[lp:~stellarium/stellarium/corona]

7823. By Alexander Wolf on 2015-08-15

obvious fix for scaling texture of the corona

7824. By Alexander Wolf on 2015-08-15

Fixed Sun's magnitude during solar eclipse

[Alexander Wolf (alexwolf)]

Fabien, is it possible reuse the calculations from shaders (I mean final_illumination)?

[gzotti (georg-zotti)]

Very welcome! Some improvements noted below.
During totality sky is dark, to see text you should also fix StelCore::isBrightDaylight().

review: Needs Fixing

[lp:~stellarium/stellarium/corona]

7825. By Alexander Wolf on 2015-09-03

few improvements for Sun's corona drawing and calculate brightness of the Sun during solar eclipse

7826. By Alexander Wolf on 2015-09-04

sunc with trunk

7827. By gzotti on 2015-09-04

better balancing for Corona brightness
Added Planet infostring on eclipse percentage

7828. By gzotti on 2015-09-04

Added new Corona texture (2008 eclipse, own work)

Unmerged revisions

=== modified file 'src/core/StelCore.cpp'
--- src/core/StelCore.cpp	2015-08-28 17:09:08 +0000
+++ src/core/StelCore.cpp	2015-09-03 13:04:16 +0000
@@ -1914,8 +1914,14 @@
 // return if sky plus atmosphere is bright enough from sunlight so that e.g. screen labels should be rendered dark.
 bool StelCore::isBrightDaylight() const
 {
-	const Vec3d& sunPos = GETSTELMODULE(SolarSystem)->getSun()->getAltAzPosGeometric(this);
-	return sunPos[2] > -0.12; // Nautical twilight (0.12 > sin (6 deg),
+	bool r = false;
+	SolarSystem* ssys = GETSTELMODULE(SolarSystem);
+	const Vec3d& sunPos = ssys->getSun()->getAltAzPosGeometric(this);
+	if (sunPos[2] > -0.12) // Nautical twilight (0.12 > sin (6 deg))
+		r = true;
+	if (ssys->getEclipseFactor(this)<=0.01) // Total solar eclipse
+		r = false;
+	return r;
 }
 
 double StelCore::getCurrentEpoch() const

=== modified file 'src/core/StelSkyDrawer.cpp'
--- src/core/StelSkyDrawer.cpp	2015-08-16 14:07:29 +0000
+++ src/core/StelSkyDrawer.cpp	2015-09-03 13:04:16 +0000
@@ -466,6 +466,25 @@
 	return true;
 }
 
+<<<<<<< TREE
+=======
+// Draw's the Sun's corona during a solar eclipse on Earth.
+void StelSkyDrawer::drawSunCorona(StelPainter* painter, const Vec3f& v, float radius, const Vec3f& color, const float alpha)
+{
+	texSunCorona->bind();
+	glEnable(GL_BLEND);
+	glBlendFunc(GL_ONE, GL_ONE);
+	painter->enableTexture2d(true);
+
+	Vec3f win;
+	painter->getProjector()->project(v, win);
+	painter->setColor(color[0], color[1], color[2], alpha);
+	painter->drawSprite2dMode(win[0], win[1], radius);
+
+	postDrawPointSource(painter);
+}
+
+>>>>>>> MERGE-SOURCE
 
 // Terminate drawing of a 3D model, draw the halo
 void StelSkyDrawer::postDrawSky3dModel(StelPainter* painter, const Vec3f& v, float illuminatedArea, float mag, const Vec3f& color)

=== modified file 'src/core/StelSkyDrawer.hpp'
--- src/core/StelSkyDrawer.hpp	2015-08-16 14:07:29 +0000
+++ src/core/StelSkyDrawer.hpp	2015-09-03 13:04:16 +0000
@@ -80,6 +80,11 @@
 
 	bool drawPointSource(StelPainter* sPainter, const Vec3f& v, const RCMag &rcMag, const Vec3f& bcolor, bool checkInScreen=false);
 
+<<<<<<< TREE
+=======
+	void drawSunCorona(StelPainter* painter, const Vec3f& v, float radius, const Vec3f& color, const float alpha);
+
+>>>>>>> MERGE-SOURCE
 	//! Terminate drawing of a 3D model, draw the halo
 	//! @param p the StelPainter instance to use for this drawing operation
 	//! @param v the 3d position of the source in J2000 reference frame

=== modified file 'src/core/modules/Planet.cpp'
--- src/core/modules/Planet.cpp	2015-08-23 19:16:48 +0000
+++ src/core/modules/Planet.cpp	2015-09-03 13:04:16 +0000
@@ -870,9 +870,19 @@
 {
 	if (parent == 0)
 	{
-		// sun, compute the apparent magnitude for the absolute mag (4.83) and observer's distance
+		// Sun, compute the apparent magnitude for the absolute mag (V: 4.83) and observer's distance
+		// Hint: Absolute Magnitude of the Sun in Several Bands: http://mips.as.arizona.edu/~cnaw/sun.html
 		const double distParsec = std::sqrt(core->getObserverHeliocentricEclipticPos().lengthSquared())*AU/PARSEC;
-		return 4.83 + 5.*(std::log10(distParsec)-1.);
+
+		// check how much of it is visible
+		const SolarSystem* ssm = GETSTELMODULE(SolarSystem);
+		double shadowFactor = ssm->getEclipseFactor(core);
+		// See: Hughes, D. W., Brightness during a solar eclipse // Journal of the British Astronomical Association, vol.110, no.4, p.203-205
+		// URL: http://adsabs.harvard.edu/abs/2000JBAA..110..203H
+		if(shadowFactor < 0.0128)
+			shadowFactor = 0.0128;
+
+		return 4.83 + 5.*(std::log10(distParsec)-1.) - 2.5*(std::log10(shadowFactor));
 	}
 
 	// Compute the angular phase
@@ -1515,6 +1525,13 @@
 		StelPainter sPainter(core->getProjection(StelCore::FrameJ2000));
 		Vec3d tmp = getJ2000EquatorialPos(core);
 		core->getSkyDrawer()->postDrawSky3dModel(&sPainter, Vec3f(tmp[0], tmp[1], tmp[2]), surfArcMin2, getVMagnitudeWithExtinction(core), color);
+<<<<<<< TREE
+=======
+
+		float eclipseFactor = ssm->getEclipseFactor(core);
+		if (core->getCurrentLocation().planetName == "Earth" && eclipseFactor<0.001f)
+			core->getSkyDrawer()->drawSunCorona(&sPainter, Vec3f(tmp[0], tmp[1], tmp[2]), 2.f*screenSz, color, 1.0 - eclipseFactor * 1000);
+>>>>>>> MERGE-SOURCE
 	}
 }
 

=== modified file 'src/core/modules/SolarSystem.cpp'
--- src/core/modules/SolarSystem.cpp	2015-08-18 18:33:37 +0000
+++ src/core/modules/SolarSystem.cpp	2015-09-03 13:04:16 +0000
@@ -1738,3 +1738,77 @@
 {
 	return getEarth()->getApparentMagnitudeAlgorithmString();
 }
+
+double SolarSystem::getEclipseFactor(const StelCore* core) const
+{
+	Vec3d Lp = sun->getEclipticPos();
+	Vec3d P3 = core->getObserverHeliocentricEclipticPos();
+	const double RS = sun->getRadius();
+
+	double final_illumination = 1.0;
+
+	foreach (const PlanetP& planet, systemPlanets)
+	{
+		if(planet == sun || planet == core->getCurrentPlanet())
+			continue;
+
+		Mat4d trans;
+		planet->computeModelMatrix(trans);
+
+		const Vec3d C = trans * Vec3d(0, 0, 0);
+		const double radius = planet->getRadius();
+
+		Vec3d v1 = Lp - P3;
+		Vec3d v2 = C - P3;
+
+		const double L = v1.length();
+		const double l = v2.length();
+
+		v1 = v1 / L;
+		v2 = v2 / l;
+
+		const double R = RS / L;
+		const double r = radius / l;
+		const double d = ( v1 - v2 ).length();
+
+		if(planet->englishName == "Moon")
+			v1 = planet->getHeliocentricEclipticPos();
+
+		double illumination;
+
+		// distance too far
+		if(d >= R + r)
+		{
+			illumination = 1.0;
+		}
+		// umbra
+		else if(r >= R + d)
+		{
+			illumination = 0.0;
+		}
+		// penumbra completely inside
+		else if(d + r <= R)
+		{
+			illumination = 1.0 - r * r / (R * R);
+		}
+		// penumbra partially inside
+		else
+		{
+			const double x = (R * R + d * d - r * r) / (2.0 * d);
+
+			const double alpha = std::acos(x / R);
+			const double beta = std::acos((d - x) / r);
+
+			const double AR = R * R * (alpha - 0.5 * std::sin(2.0 * alpha));
+			const double Ar = r * r * (beta - 0.5 * std::sin(2.0 * beta));
+			const double AS = R * R * 2.0 * std::asin(1.0);
+
+			illumination = 1.0 - (AR + Ar) / AS;
+		}
+
+		if(illumination < final_illumination)
+			final_illumination = illumination;
+	}
+
+	return final_illumination;
+}

=== modified file 'src/core/modules/SolarSystem.hpp'
--- src/core/modules/SolarSystem.hpp	2015-08-03 13:17:06 +0000
+++ src/core/modules/SolarSystem.hpp	2015-09-03 13:04:16 +0000
@@ -331,6 +331,9 @@
 	//! Reload the planets
 	void reloadPlanets();
 
+	//! Determines relative amount of sun visible from the observer's position.
+	double getEclipseFactor(const StelCore *core) const;
+
 	///////////////////////////////////////////////////////////////////////////////////////
 	// DEPRECATED
 	///////////////////////////////////////////////////////////////////////////////////////