Correct atmospheric scattering for trees, where we were applying ambient lighting twice, making them too dark, and not using an alpha test.

Also fix the tropical trees, where only half the texture was defined.

Effects/tree.eff

@@ -68,6 +68,10 @@
 				<source>src-alpha</source>
 				<destination>one-minus-src-alpha</destination>
 			</blend>
+			<alpha-test>
+				<comparison>gequal</comparison>
+				<reference type="float">0.1</reference>
+			</alpha-test>
 			<texture-unit>
 				<unit>0</unit>
 				<type>2d</type>
@@ -107,6 +111,10 @@
 				<wrap-s>clamp</wrap-s>
 				<wrap-t>clamp</wrap-t>
 			</texture-unit>
+			<alpha-test>
+				<comparison>gequal</comparison>
+				<reference type="float">0.1</reference>
+			</alpha-test>
       <program>
         <vertex-shader>Shaders/tree-haze.vert</vertex-shader>
         <fragment-shader>Shaders/tree-haze.frag</fragment-shader>

Shaders/tree-haze.vert

@@ -95,7 +95,7 @@ void main()
 
   vec4 diffuse_color = gl_FrontMaterial.diffuse * max(0.1, n);
   //diffuse_color.a = 1.0;
-  vec4 ambient_color = gl_FrontLightModelProduct.sceneColor + gl_LightSource[0].ambient * gl_FrontMaterial.ambient;
+  vec4 ambient_color = gl_FrontMaterial.ambient;
 
     // here start computations for the haze layer
     // we need several geometrical quantities