A_SpawnParticles: allow negative fadestep

[D2JK]

I wanted to create particles that fade in over time (increasing alpha), but specifying a negative value as the fadestep parameter has no effect currently. Could this be changed?

I would then expect the particle to abruptly disappear at the end of its lifetime, which would be fine with me.

[Nash]

Wouldn't it be better to add a separate fade-in parameter (I know, more params, yikes), rather than piggyback on what is meant for fading out? What if you want to create a particle that has both fade-ins and fade-outs.