Particle Systems intentional delay of 0.02?

[muhammadreza]

@richardkettlewell

The Scene view uses a custom solution to let you see in between the discrete update steps of the simulation. We may not do the first update until the time is 0.02, when setting the preview time in the scene view (i dont recall the exact number)

We do deterministic updates at these fixed intervals so the playback in repeatable, and we can guarantee the effect looks the same every time it is played.

You can disable it explicitly in script by doing:

float tinyStep = 0.000001f;
ps.Simulate(tinyStep, true, true, false);
ps.Play(); // Because Simulate leaves the system in a paused state

as per https://docs.unity3d.com/ScriptReference/ParticleSystem.Simulate.html

That final “false” says “ignore the fixed timestep stuff and just advance the simulation by the exact amount i requested”

you saved my day, thanks!

[Max_Bol]

@richardkettlewell

Assuming you are using Rate over Time emission? In which case, particles are spawned at the end of the emission interval.

Eg, rate over time of 10, will emit a particle at 0.1, 0.2 etc.

So there will never be an emission exactly at time 0 with this mode.

You can get an emission event exactly at time 0 with a burst.

Hope this helps explain the behaviour you are seeing!

I can confirm that this is not exactly true (for the Burst) or, at least, not within the scope of certain setups if the particle system Culling Mode is set to Pause & Catch up or Pause. If the particle system is set with either of those two Culling Mode, a burst particle that is not prewarm (which requires it to be looped) will results in a significant delay while within the camera field of view if it has not been seen yet by the camera.

I have build a system that generate a map for a side scrolling RPG and it includes rocks, grasses and trees that are particles meshes in the background and foreground. I have build my own culling system based on the NPCs and players’ position so that physics and path finding doesn’t take too much of a toll.

If I set the Culling Mode of those to anything else than Automatic or Always Simulating, there’s as much as 1 second of delay before a particle appears on the camera even while the editor runs at 200+ FPS and that’s regardless of if the particle was initially played or not as long as it was outside of any camera views while initially active.

For example, if I ran the editor in Play mode without the Scene view active, the delays was highly noticeable and if i looked at it while in the Scene view, there were no delays because the Scene view was forcing the rendering of the particles to be active and not paused.

The work around I have implemented (which luckily for me could be implemented in the way I managed the particles systems for each block in my scene) is to initially set my particles system to “AlwaysSimulate” once instantiated, then play(); it, then on the next frame switching it culling mode to “Pause” (in my case).

The reason why I wanted it to Pause is because those particles of mine are set with a life time of Infinity as, once spawned, I don’t need it to simulate anything anymore (and just stay still), but just stays as-is. (As it’s part of the foreground and background, there’s no need for physics or interaction.) Setting its Culling mode to Pause boost the performance by 15% in my scene.

If someone had a lots of particles in a scene and wanted to use the Pause & Catch up mode for some gain in performances, my work around is kinda necessary currently for it to work properly.