+void Lighting::set_fog_color(const Color &c)
+{
+ fog_color = c;
+}
+
+void Lighting::set_fog_density(float d)
+{
+ if(d<0)
+ throw invalid_argument("Lighting::set_fog_density");
+
+ fog_density = d;
+}
+
+void Lighting::set_fog_half_distance(float d)
+{
+ set_fog_density(-log(pow(0.5, 1.0/d)));
+}
+