From 543f1b790289b0173fdcbecec5c810e7a3e0d471 Mon Sep 17 00:00:00 2001
From: Torsten Dreyer <Torsten@t3r.de>
Date: Wed, 8 Oct 2014 12:45:01 +0200
Subject: [PATCH] Set sun color below horizon

Thorsten Renk:
The following patch sets the sun color to alpha=0 when
the sun is below the local horizon, removing the oddity
that the sun is seen 'through' the terrain when the terrain
at large distance is rendered by the skydome.
---
 simgear/scene/sky/oursun.cxx | 12 +++++++++++-
 simgear/scene/sky/oursun.hxx |  1 +
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/simgear/scene/sky/oursun.cxx b/simgear/scene/sky/oursun.cxx
index a267034f..f4b049ee 100644
--- a/simgear/scene/sky/oursun.cxx
+++ b/simgear/scene/sky/oursun.cxx
@@ -52,7 +52,7 @@ using namespace simgear;
 // Constructor
 SGSun::SGSun( void ) :
     visibility(-9999.0), prev_sun_angle(-9999.0), path_distance(60000.0),
-    sun_exp2_punch_through(7.0e-06)
+    sun_exp2_punch_through(7.0e-06), horizon_angle(0.0)
 {
 
 }
@@ -341,6 +341,13 @@ bool SGSun::repaint( double sun_angle, double new_visibility ) {
         gamma_correct_rgb( scene_color._v );
         gamma_correct_rgb( sun_color._v );
 
+	if (sun_angle >91.0 * 3.1415/180.0 + horizon_angle)
+		{
+		sun_color[3] = 0;
+		o_halo_color[3]=0;
+		i_halo_color[3]=0;
+		}
+
         (*sun_cl)[0] = sun_color;
         sun_cl->dirty();
         (*scene_cl)[0] = scene_color;
@@ -404,6 +411,9 @@ bool SGSun::reposition( double rightAscension, double declination,
 
          if ( alt_half < 0.0 ) alt_half = 0.0;
 
+	 //angle at which the sun is visible below the horizon
+	 horizon_angle = acos(r_earth/position_radius);
+
          // Push the data to the property tree, so it can be used in the enviromental code
          if ( env_node ){
             env_node->setDoubleValue( "atmosphere/altitude-troposphere-top", r_tropo - r_earth );
diff --git a/simgear/scene/sky/oursun.hxx b/simgear/scene/sky/oursun.hxx
index 3414c862..bd1f3db1 100644
--- a/simgear/scene/sky/oursun.hxx
+++ b/simgear/scene/sky/oursun.hxx
@@ -51,6 +51,7 @@ class SGSun : public SGReferenced {
     // distance of light traveling through the atmosphere
     double path_distance;
     double sun_exp2_punch_through;
+    double horizon_angle;
 
     SGPropertyNode_ptr env_node;