It seems that a Sprite is pretty much a MovieClip without a timeline (although there are other static/dynamic property issues too, they don’t come into play in this particular piece of code), so a Sprite makes more sense to use than a MC, and will indeed speed things up, but by a very small amount – but hey, it all counts!

I hadn’t noticed the null reference was introduced when I recently updated the code to remove the particles as soon as they’re entirely transparent or above the stage – I was just trying to eke out every bit of performance I knew how by removing particles from the stage as soon as I possibly could.

The unintended side effect of this was that flash then tries to remove the particles twice:
- Once when they’re transparent or above the stage (called from within the SmokeParticle Class), and
- Again when the particle limit gets rid of the oldest particle (i.e. array element 0) to add a new particle (called from the main flash file)

Hence the null pointer reference for any particle that has already been “removed” when the transparent/above remover kicked in from the updateParticle function.

If you comment out the parent.removeChild(this); line in the ParticleDestructor function, normal service is resumed, but performance suffers because we’re not eliminating the particle as soon as we possibly can.

I’ll have a look at the code again this evening and either wrap the removeChild calls in some conditions, or add a SmokeParticle property to keep track of whether the particle’s already been removed so hopefully we can keep our speed gain from nuking the particle early, but lose the null-pointer shenanigans

Update: Done!