VFX instances fail to batch when Set Lifetime is disabled

6.5.X

As Designed

Thank you for reporting a bug to Unity. After reviewing the behavior, we've confirmed it aligns with the current design and intended use of the feature. We understand this may differ from your expectations or workflow. VFX instancing does not always batch drawcalls, it depends on a number of conditions. In this particular case, the drawcalls are not batched when Set Lifetime is disabled because they become immortal particles. Particle systems with immortal particles have a fixed number of particles which allows us to draw the exact number of particles instead of the total capacity. Each instance could have a different particle count, so, if we rendered them batched, we would have to determine which instance they belong to in the vertex shader, which has a cost (especially for mesh outputs). Other features, like draw indirect, also trigger separate drawcalls. However, having more drawcalls does not always mean worse performance. Those drawcalls are queued one after another and don't require setting up the shader properties again, so they are faster than other drawcalls. You can find more information here: https://discussions.unity.com/t/vfx-graph-instancing-not-working/1592121/4 We will close this case as 'As Designed.' If you have feedback on how the feature could better meet your needs, please let us know - we value your input and consider it in future improvements.