Better balance for stellar visibility in twilight and moonlight

src/core/modules/Atmosphere.hpp

@@ -109,13 +109,33 @@ class Atmosphere
 	//! Get the light pollution luminance in cd/m^2
 	float getLightPollutionLuminance() const { return lightPollutionLuminance; }
 
+	//! Get the multiplier applied to averageLuminance when computing the
+	//! star-visibility adaptation luminance reported to StelSkyDrawer.
+	//! Each atmosphere model produces averageLuminance in a different scale,
+	//! so this multiplier must be tuned per model.  The default (1000) is
+	//! calibrated for the Preetham/Schaefer model to reach full stellar
+	//! visibility at approximately -18 deg sun altitude (astronomical twilight).
+	//! ShowMySky uses the same value (see AtmosphereShowMySky.hpp).
+	virtual float getStarAdaptationMultiplier() const { return 1000.f; }
+
+	//! Store the natural sky adaptation luminance for atmosphere rendering.
+	//! This is the un-inflated value used by the atmosphere shader so that
+	//! the sky tone-maps correctly even when the star-visibility adaptation
+	//! luminance reported via StelSkyDrawer::reportLuminanceInFov() differs.
+	void setSkyAdaptationLuminance(float lum) { skyAdaptationLuminance = lum; }
+	//! Get the natural sky adaptation luminance stored for atmosphere rendering.
+	float getSkyAdaptationLuminance() const { return skyAdaptationLuminance; }
+
 protected:
 	//! The average luminance of the atmosphere in cd/m2
 	float averageLuminance = 0;
 	bool overrideAverageLuminance = false; // if true, don't compute but keep value set via setAverageLuminance(float)
 	float eclipseFactor = 1;
 	LinearFader fader;
 	float lightPollutionLuminance = 0;
+	//! Natural sky adaptation luminance for atmosphere shader tone-mapping,
+	//! decoupled from the star-visibility adaptation luminance.
+	float skyAdaptationLuminance = 50.f;
 };
 
 #endif // ATMOSPHERE_HPP

src/core/modules/AtmospherePreetham.cpp

@@ -398,6 +398,12 @@ void AtmospherePreetham::draw(StelCore* core)
 
 	StelToneReproducer* eye = core->getToneReproducer();
 
+	// Temporarily set the natural sky adaptation luminance for the
+	// tone-mapping shader uniforms, in case the star-visibility
+	// adaptation luminance differs (see LandscapeMgr.cpp).
+	float savedLwa = eye->getWorldAdaptationLuminance();
+	eye->setWorldAdaptationLuminance(skyAdaptationLuminance);
+
 	StelPainter sPainter(core->getProjection2d());
 	sPainter.setBlending(true, GL_ONE, GL_ONE);
 
@@ -406,6 +412,9 @@ void AtmospherePreetham::draw(StelCore* core)
 	bool useTmGamma, sRGB;
 	eye->getShadersParams(a, b, c, d, useTmGamma, sRGB);
 
+	// Restore the star-visibility Lwa
+	eye->setWorldAdaptationLuminance(savedLwa);
+
 	GL(atmoShaderProgram->setUniformValue(shaderAttribLocations.alphaWaOverAlphaDa, a));
 	GL(atmoShaderProgram->setUniformValue(shaderAttribLocations.oneOverGamma, b));
 	GL(atmoShaderProgram->setUniformValue(shaderAttribLocations.term2TimesOneOverMaxdLpOneOverGamma, c));

src/core/modules/AtmosphereShowMySky.cpp

@@ -809,12 +809,23 @@ void AtmosphereShowMySky::draw(StelCore* core)
 	if (!atm_intensity)
 		return;
 
+	// Temporarily set the natural (un-inflated) sky adaptation luminance
+	// for the tone-mapping shader uniforms. The global Lwa has been inflated
+	// (via a large star-adaptation multiplier) to suppress stars during
+	// twilight, but the sky must still tone-map with the real atmospheric
+	// luminance so it looks blue during the day.
+	float savedLwa = eye->getWorldAdaptationLuminance();
+	eye->setWorldAdaptationLuminance(skyAdaptationLuminance);
+
 	GL(luminanceToScreenProgram_->bind());
 
 	float a, b, c, d;
 	bool useTmGamma, sRGB;
 	eye->getShadersParams(a, b, c, d, useTmGamma, sRGB);
 
+	// Restore the inflated Lwa so star rendering continues to use it
+	eye->setWorldAdaptationLuminance(savedLwa);
+
 	GL(luminanceToScreenProgram_->setUniformValue(shaderAttribLocations.alphaWaOverAlphaDa, a));
 	GL(luminanceToScreenProgram_->setUniformValue(shaderAttribLocations.oneOverGamma, b));
 	GL(luminanceToScreenProgram_->setUniformValue(shaderAttribLocations.term2TimesOneOverMaxdLpOneOverGamma, c));

src/core/modules/AtmosphereShowMySky.hpp

@@ -57,6 +57,11 @@ class AtmosphereShowMySky : public Atmosphere, public QObject
 	bool isReadyToRender() const override;
 	LoadingStatus stepDataLoading() override;
 
+	//! ShowMySky produces averageLuminance in a much smaller scale than
+	//! Preetham/Schaefer, so a larger multiplier is needed to correctly
+	//! suppress stars during twilight until astronomical twilight (-18°).
+	float getStarAdaptationMultiplier() const override { return 1000.f; }
+
 private:
 #ifdef ENABLE_SHOWMYSKY
 	QLibrary showMySkyLib;

src/core/modules/LandscapeMgr.cpp

@@ -539,7 +539,19 @@ void LandscapeMgr::update(double deltaTime)
 		resetToFallbackAtmosphere();
 	}
 
-	core->getSkyDrawer()->reportLuminanceInFov(3.75f+atmosphere->getAverageLuminance()*3.5f, true);
+	// Store the natural sky adaptation luminance for atmosphere shader
+	// tone-mapping, using the original Preetham-era multiplier (3.5).
+	// This keeps the sky rendering identical to the original code.
+	atmosphere->setSkyAdaptationLuminance(3.75f + atmosphere->getAverageLuminance() * 3.5f);
+
+	// Report the star-visibility adaptation luminance using a per-model
+	// multiplier.  ShowMySky produces much smaller averageLuminance values
+	// than Preetham/Schaefer, so it needs a larger multiplier (~1000) to
+	// correctly suppress stars until astronomical twilight (-18 deg).
+	// Preetham uses ~12 (derived from the twilight brightness ratio between
+	// -8 deg and -18 deg applied to the original 3.5 multiplier).
+	const float starMult = atmosphere->getStarAdaptationMultiplier();
+	core->getSkyDrawer()->reportLuminanceInFov(3.6f + atmosphere->getAverageLuminance() * starMult, true);
 
 	// NOTE: Simple workaround for brightness of landscape when observing from the Sun.
 	if (currentPlanet->getID() == sun->getID())

src/core/modules/MilkyWay.cpp

@@ -327,7 +327,7 @@ void main(void)
 	const float nelm = StelCore::luminanceToNELM(drawer->getLightPollutionLuminance());
 	const float bortleIntensity = 1.f+(15.5f-2*nelm)*atmFadeIntensity; // smoothed Bortle index moderated by atmosphere fader.
 
-	const float lum = drawer->surfaceBrightnessToLuminance(12.f+0.15f*bortleIntensity); // was 11.5; Source? How to calibrate the new texture?
+	const float lum = drawer->surfaceBrightnessToLuminance(14.f+0.15f*bortleIntensity); // was 11.5; Source? How to calibrate the new texture?
 
 	// Get the luminance scaled between 0 and 1
 	float aLum =eye->adaptLuminanceScaled(lum*fader->getInterstate());