Hi,
I was wondering if there is some kind of a best practice in using KCM to prevent particles from being visible to the alpha channel. For example if I want particles to become visible only if they have reached a certain speed. Any suggestions are very much apprecitaed, since I just have some kind of a blackout.
There are two approaches to this - you can set the Density channel to 0.0 when the Velocity Magnitude is below a certain Threshold, or, since you are asking for the Best Practice, you can set the Selection channel to 0.0 instead and drop a Krakatoa Delete modifier on the stack, so the affected particles will not even loading into memory. In the latter case, you will render less particles and thus reduce the total render time!
Your flow would be something like
The reason this works is because the Boolean Less operator produces an Integer value of 0 when the comparison is FALSE, which, when converted ToFloat, feeds a 0.0 into the Selection channel. When the comparison is TRUE, it outputs 1.0. So when the Velocity Magnitude is Less than the Threshold (in my case 150.0 units per second), the output is 1.0 and the particle gets marked as selected in its Selection channel, telling the Krakatoa Delete to delete it.
It probably makes sense to do it less literally and fade up the density based on velocity and then delete any particle who’s density is below a certain threshold. This way you don’t get pops from particles appearing. Depends on your exact needs.
True. It depends on how the question is asked.
Next week I will use this in the Webinar as a starting point for various demonstrations 
