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tylerjenningsw
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The simulation runs from layer time 0, but it used the Birth Rate of the rendered frame for every step. A rate keyed from 3 down to 0 simulated no births at all once it reached 0, so the burst's particles vanished that frame although their Longevity had not run out. A ramped rate was simulated as if its current value had always applied. Each step now samples Birth Rate at its own layer time through EffectHost::param_at (with the effect's own index). Without such a host the current value applies throughout, as before. Particles already alive keep moving and ageing whatever the rate. The carry and particle ids continue across rate changes. Birth Rate is left out of the simulation cache key, so an animated rate no longer restarts the simulation every frame. In its place: - The CPU state keeps a hash of the rates it was stepped with (hist). A checkpoint is resumed only when that matches the current history, so moving an earlier key is never served from a stale checkpoint. - The GPU gets the birth schedule of the sampled rates (births_at). Its checkpoints record which births they hold, and are resumed only when the request's births before that step are the same. A constant Birth Rate gives exactly the particles it did. CC Particle Systems II and CC Mr. Mercury keep their constant-rate simulation.