Very cool! It looks very realistic near the trees. It seems like shadows/lighting look more natural with this method. So, the only thing you upload from host to device(gpu) are point positions and those 4 attributes? That’s very neat!
Recently, I’ve had to wrestle with lots of hairy issues where the OpenGL polydata mapper would refuse to work in webassembly because it had some non-portable code. Since all of your work is in early development stages, do you plan for your code to run in webassembly as well? Are you making an active effort to ensure your OpenGL contributions to VTK are compatible with GLES 3.0 spec? I’m asking this because we are now taking webassembly, as a supported platform, more seriously than before 
Geometry shaders are not supported in webgl2. So, it’d be nice to avoid them.