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Particle system behavior changes when it is rotated or scaled in negative axis

Visual Effects - Legacy


How to reproduce:
1. Open the attached scene ("")
2. Open the repro scene ("SampleScene")
3. Inspect the particle effects

Expected results: Particle systems behave the same way, as the only difference between them is rotation or scaling
Actual results: Particles behavior changes (see the attached videos)

Reproducible with: 2018.3.0b3, 2018.3.3f1, 2019.1.0b1, 2019.2.0a3
Not reproducible with: 2017.4.19f1, 2018.3.0b2

1. The only difference between the smoke rings are the rotations of particle systems, and the only difference between flame particles is the Y-axis scale

  1. Resolution Note:

    The results here may have changed due to fixes we made for non-uniformly scaled systems in 2018.3. Those fixes were made for setups where non-uniform scale was valid to use (eg local or world aligned particles).

    What you have here are camera-aligned particles. It is never valid to use non-uniform scale on such systems, because we must arbitrarily choose whether to use the camera or the transform rotation, as the basis for how to apply the scale, and both look weird in various situations.

    We recommend changing the Scaling Mode to be Local or Shape, to ignore the non-uniform scale of the parent, or use the size modules to control the non-uniform sizes in a space local to each particle billboard.

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