Tick Time - Game Thread
Tick Time represents the amount of time spent updating particle systems in the scene. Tick Time can be viewed with the stat particles command which lists out all relative information required to assess particle evaluation costs.
There are many methods which can be used to reduce Tick costs.
Tick Time is directly influenced by the number of active EmitterActors in your scene. The more active emitters in the scene, the higher Tick Time will be. Emitters should only be set to autoActivate if they are required to loop when the level starts.
If large amounts of sprites/explosions/burst effects are visible on level load in the editor, these effects are automatically evaluated at run time and can cause visible hitching when a level is loaded.
A Particle Parameter can be used in an effect to allow for position offsets once the effect is placed in the world. By using a particle parameter, it is possible to reduce emitter counts, which reduces tick cost overall. Particle Parameters can be setup by selecting particleParameter from the distribution list in the module for the individual setting.
It is possible to stream out and disable EmitterActors when they are not in view, or if they are associated with an area of a level which is no longer in memory. Streaming EmitterActors with level geometry is a good practice to reduce tick overhead. In some cases where atmospheric effects are heavy, Blueprint actions can be used to toggle atmosphere off and on during combat sequences to lower tick time and overdraw.
Particle Systems loaded into memory, but out of view (say on the floor above you) can also be toggled with Blueprint actions and streaming volumes to reduce evaluation costs.
In some cases, a mesh effect can be a good replacement for a particle system. A placed Static Mesh does not have an evaluation cost on the Game Thread. In many cases it is more beneficial to place a Static Mesh as a replacement for a particle system. This includes vista effects, fog effects etc.
Particle counts play directly into evaluation cost. The more particles in a scene, and the longer they live, the more evaluation is required. Limiting lifespan to the duration required for the effect is good practice all around.
Enabling LODs in particle systems allows for lower particle emissions when a system is not within optimal viewing range. It may help to think of your effect in terms of a hero state, and an acceptable level of lower quality for longer viewing distances. Tightening LODs to required distances can go a long way to lowering evaluation costs in a scene without dramatically losing visual quality.
Check your effects for expensive evaluation costs which can be lowered such as collisions, non-fixed bounds, and spawn per unit counts which are too high. Setting bounds to a fixed state can increase performance significantly and should be used whenever possible.