Here are some articles about how to do billboarding in the vertex shader and in the geometry shader in GLSL.
- Simple Billboarding Vertex Shader:
http://www.geeks3d.com/20140807/billboarding-vertex-shader-glsl/
- Particle Billboarding with the Geometry Shader:
http://www.geeks3d.com/20140815/particle-billboarding-with-the-geometry-shader-glsl/
GLSL Hacker demos that illustrate these articles can be found in the code sample pack (http://www.geeks3d.com/glslhacker/cs/)
- host_api/GLSL_Billboarding/
- host_api/GLSL_Billboarding_Geometry_Shader/
(http://www.ozone3d.net/public/jegx/201408/glslhacker_billboarding_geometry_shader_particles_02.jpg)