commit 6544040fbff46ffb1078fde295fe5b5efd3a80a6
Author: Leszek Koltunski <leszek@koltunski.pl>
Date:   Tue Jul 3 13:47:02 2018 +0100

    Fix the fact that back-facing surfaces were invisible.

diff --git a/src/main/res/raw/main_fragment_shader.glsl b/src/main/res/raw/main_fragment_shader.glsl
index 60b9953..7715a29 100644
--- a/src/main/res/raw/main_fragment_shader.glsl
+++ b/src/main/res/raw/main_fragment_shader.glsl
@@ -126,10 +126,13 @@ void main()
     }
 #endif
 
-  vec4 converted = vec4(color.rgb * (1.0 + 7.0*v_Normal.z) * 0.125, color.a);
+  float z = v_Normal.z;
+  if( z<0.0 ) z = -z;
+
+  vec4 converted = vec4(color.rgb * (1.0 + 7.0*z) * 0.125, color.a);
 
 #ifdef OIT
-  if( converted.a > 0.95 )
+  if( converted.a > 0.97 )
     {
     fragColor= converted;
     }
diff --git a/src/main/res/raw/oit_build_fragment_shader.glsl b/src/main/res/raw/oit_build_fragment_shader.glsl
index 2cbcbe2..3ad6b4d 100644
--- a/src/main/res/raw/oit_build_fragment_shader.glsl
+++ b/src/main/res/raw/oit_build_fragment_shader.glsl
@@ -98,7 +98,7 @@ void main()
   vec4  color= texture(u_Texture     , v_TexCoordinate);
   float depth= texture(u_DepthTexture, v_TexCoordinate).r;
 
-  if( color.a > 0.95 )
+  if( color.a > 0.97 )
     {
     gl_FragDepth = depth;
     fragColor    = color;