finally a nicer sprite lightmap creation is ready, replacing the random one, as Jcl suggested by creating temporary models to get exact image alpha, taking into account x2 x3 sprite property too. there are a couple of tricky settings e.g. accuracy of multiple hits (limits length of c_trace-chain of a terrain pixel), alpha treshold value, shadow darkness, 2 types of shadows generated atuomatically: a darker for non-alpha hits, and a lighter for terrain and for too many alpha hits (it can be modified by alpha accuracy).
another feature completed for the new release.