The easiest way perhaps is to animate the model in your modeler software then export the animation. Anyway i don't know if this will be fast because you will need to animate lot of entities.
The most efficient way should be to have 1 mesh containing all the grass, then animating only the needed vertex or moving the textures...
The problem is that you should clusterize that mesh to render only the viewing zone...
The most efficient way should be to have 1 mesh containing all the grass, then animating only the needed vertex or moving the textures...
The problem is that you should clusterize that mesh to render only the viewing zone...