How to emit particles only in one direction


#1

Hi there,

for a special case I need an emitter of particles to emit in only one direction and not always face the particles to the viewer. I don’t get it how to do that - is it possible in general? Someone knows how to do that?

Thank you :slight_smile:


#2

From what I have seen, I believe you can set the spin to follow the emitter.


#3

You can’t, and the spin won’t change this. It will only rotate it around the axis going your face.
(even id the spin is set to follow or not the emitter)


#4

Okay, that’s what I figured out also. Do you know this will come up sometime? Would be a nice feature to simulate a projector - but maybe it’s the nature of a particle to always face the viewer…

Thank you anyway @Vegaslon and @Alezia.Kurdis


#5

Yes, it is in the nature of particles to always face the viewer. Particles, as a concept in 3D, are really a hack to do quick rendering of small objects that would generally look the same from any direction anyway, hence the always-face-the-viewer is an inherent part of this: They can just be scaled in 2d space and drawn without a lot of extra rotation or complex lighting calculations, so lend themselves to much larger quantities than you could get away with for 3D objects in a scene. They are also not intended to look any good above the size of, well, particles! :wink: Plus, they are generally rendered psudo-randomly client-side and so, close-up, will look subtly different on each client (for clouds of particles - their intended use, the cloud as a whole will look pretty much the same (assuming you are using enough particles for them to positionally average properly through the volume they are intended to fill), but the individual particles making it up can vary in position quite a bit.)

I believe (IRRC) the name of what you actually want is a ‘billboard’ (2D object rendered into 3D space with its own defined position and rotation within that 3D space). This sort of object is more of a half-way between particles and a full 3D object, being simpler and quicker to calculate, having only 2 dimensions, but with the extra load of skewing-for-perspective and lighting within the 3D world. I don’t know if HiFi has this type of object as an explicit thing, though, or if defining a normal 3D object with only 4 points defining a single plane in its structure would work (from general 3D experience, I would put money on it working from one side, but being invisible from the other).


#6

Just chiming in, all of the responses here have been correct. Our current particles are always billboarded towards the camera. You can use spin to rotate them in screen space, but you can’t make them not face the camera, as they are designed to simulate “spherical particles.”

However! We know that there are other cases where you don’t want your particles to be billboarded like that, and maybe even want non-planar particles. These are all planned improvements that are on the horizon.


#7

Great to hear, thank you for telling uns @SamGondelman :slight_smile: