Type: SystemTimeSpan The elapsed time since the last update.
startIndex
Type: SystemInt32 The index of the first particle to initialize.
count
Type: SystemInt32 The number of particles to initialize.
Remarks
Notes to Inheritors:
When this method is called, ParticleSystem is already
initialized and the particle effector is Enabled. startIndex
plus count will never exceed the maximal number of particles (= the
length of the particle parameter arrays). This method does not have to make any index
checks. (When startIndex plus count would exceed the
length of the particle parameter arrays, UpdateParticles(TimeSpan, Int32, Int32) calls
OnUpdateParticles(TimeSpan, Int32, Int32) twice.)