opengles transparency;
sample code: com.example.tutorial_opengles_transparency;
iOS, Android, Unity3D Education blog,
sample code: com.example.tutorial_opengles_transparency;
http://www.droidnova.com/android-3d-game-tutorial-part-iii,348.html
reference: http://insanitydesign.com/wp/projects/nehe-android-ports/