New label brightness formula

Author: Askaniy

src/celastro/astro.h

@@ -30,7 +30,7 @@ constexpr inline float LN_MAG = 1.0857362f; // 5/ln(100)
 
 // Lowest screen brightness of a point to render
 constexpr inline float LOWEST_IRRADIATION = 1.0f / 255.0f;
-//                                       = 1.0f / (255.0f * 12.92f); after implementing gamma correction
+//                                        = 1.0f / (255.0f * 12.92f); after implementing gamma correction
 
 namespace detail
 {

src/celengine/dsorenderer.cpp

@@ -190,8 +190,7 @@ void DSORenderer::process(DeepSkyObject* const &dso,
         float irradiationEff = astro::magToIrradiance(appMagEff) * exposure;
         if (irradiationEff > labelLowestIrradiation)
         {
-            // TODO: the label transparency is not tested, most likely need fixes
-            float distr = std::min(1.0f, step * (irradiationEff - labelLowestIrradiation) / labelLowestIrradiation);
+            float distr = irradiationEff / labelLowestIrradiation;
             labelColor.alpha(distr * labelColor.alpha());
 
             renderer->addBackgroundAnnotation(rep,

src/celengine/pointstarrenderer.cpp

@@ -101,21 +101,20 @@ void PointStarRenderer::process(const Star& star, float distance, float irradian
             if (irradiation > astro::LOWEST_IRRADIATION)
             {
                 starVertexBuffer->addStar(relPos, starColor, irradiation);
-            }
 
-            // Place labels for stars brighter than the specified label threshold brightness
-            if (((labelMode & Renderer::StarLabels) != 0) && irradiation > labelLowestIrradiation)
-            {
-                Vector3f starDir = relPos.normalized();
-                if (starDir.dot(viewNormal) > cosFOV)
+                // Place labels for stars brighter than the specified label threshold brightness
+                if (((labelMode & Renderer::StarLabels) != 0) && irradiation > labelLowestIrradiation)
                 {
-                    // TODO: the label transparency is not tested, most likely need fixes
-                    float distr = min(1.0f, 3.5f * (irradiation - labelLowestIrradiation)/labelLowestIrradiation);
-                    Color color = Color(Renderer::StarLabelColor, distr * Renderer::StarLabelColor.alpha());
-                    renderer->addBackgroundAnnotation(nullptr,
-                                                      starDB->getStarName(star, true),
-                                                      color,
-                                                      relPos);
+                    Vector3f starDir = relPos.normalized();
+                    if (starDir.dot(viewNormal) > cosFOV)
+                    {
+                        float distr = labelLowestIrradiation / irradiation;
+                        Color color = Color(Renderer::StarLabelColor, distr * Renderer::StarLabelColor.alpha());
+                        renderer->addBackgroundAnnotation(nullptr,
+                                                        starDB->getStarName(star, true),
+                                                        color,
+                                                        relPos);
+                    }
                 }
             }
         }

src/celengine/render.cpp

@@ -96,8 +96,6 @@ using namespace celestia::engine;
 using namespace celestia::render;
 using celestia::util::GetLogger;
 
-static const int REF_DISTANCE_TO_SCREEN  = 400; //[mm]
-
 // Contribution from planetshine beyond this distance (in units of object radius)
 // is considered insignificant.
 static const float PLANETSHINE_DISTANCE_LIMIT_FACTOR = 100.0f;
@@ -3739,10 +3737,7 @@ void Renderer::renderPointStars(const StarDatabase& starDB,
     starRenderer.labelMode         = labelMode;
     starRenderer.SolarSystemMaxDistance = SolarSystemMaxDistance;
 
-    // Original function
-    // float effDistanceToScreen = mmToInches((float) REF_DISTANCE_TO_SCREEN) * pixelSize * getScreenDpi(); // = 1.0 at startup
-    // starRenderer.labelThresholdMag = 1.2f * max(1.0f, (faintestMag - 4.0f) * (1.0f - 0.5f * std::log10(effDistanceToScreen)));
-    starRenderer.labelLowestIrradiation = 1.0f; // refinement is needed
+    starRenderer.labelLowestIrradiation = 1.0f;
 
     starRenderer.colorTemp = &starColors;
 
@@ -3815,11 +3810,8 @@ void Renderer::renderDeepSkyObjects(const Universe& universe,
 
     dsoRenderer.frustum = projectionMode->getInfiniteFrustum(MinNearPlaneDistance, observer.getZoom());
     // Use pixelSize * screenDpi instead of FoV, to eliminate windowHeight dependence.
-    
-    // Original function
-    // float effDistanceToScreen = mmToInches((float) REF_DISTANCE_TO_SCREEN) * pixelSize * getScreenDpi(); // = 1.0 at startup
-    // dsoRenderer.labelThresholdMag = 2.0f * max(1.0f, (faintestMag - 4.0f) * (1.0f - 0.5f * log10(effDistanceToScreen)));
-    dsoRenderer.labelLowestIrradiation = 1.0f; // refinement is needed
+
+    dsoRenderer.labelLowestIrradiation = 1.0f;
 
     using namespace celestia;
     galaxyRep      = MarkerRepresentation(MarkerRepresentation::Triangle, 8.0f, GalaxyLabelColor);