Posted by Demoscene Passivist on Apr 26, 2013; 6:36am
URL: https://forum.jogamp.org/3D-Brain-Representation-OpenGL-ES-and-Android-tp4029032p4029040.html

The technique you are searching for is called "raycasting".

The basic idea is to render a cube with a special vertex shader that interpolates ray-coordinates for a fragment shader which then casts one ray per pixel into the volume texture, thereby adding up the intensity values of the volume.

There are hundrets of implementations of this technique. I would look for a WebGL implementation because they are more or less automatically OpenGL ES (2) compatible. For example take a look here.

For the JOGL setup code you may have a look at my implementation (although I'm not sure if its ES compatible).

Another completely different approach is to simply use a stack of planes/rects where each is assigned a texture from the volume set and then use additive blending to create the illusion of a volume rendering. It has some flaws but is very easy to implement. For JOGL implementation also see my blog post here (guess it can be easily ported to ES).