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regular error in particle placement when emitter is parented to an animated null
Closed, ResolvedPublic

Description

System Information
Mac OS 10.9.2
Nvidia GTX580
Nvidia GTX560Ti

Blender Version
cdc5d65 2.70

Worked: (optional)

Short description of error
When a particle emitter is parented to a null for animation, you get a regular displacement of a single particle. This has been tested on the latest build (downloaded yesterday) and the latest release candidate (2.7a), both have the same problem.

Exact steps for others to reproduce the error

  1. Add an empty object to the default scene, not in the same location as the default cube.
  2. Parent default cube to the empty.
  3. Set rotation keyframes on the empty.
  4. Add mesh to be used as particle object
  5. add particle system to default cube
  6. Assign a single vertex to a new vertex group on the default cube.
  7. remove all field weights, including gravity, so the particles don't move once created.
  8. set density to vertex group just created.
  9. Set render to 'Object' and select the particle object.
  10. Set all 'Velocity' values to 0
  11. Set Emission number: 5000

Emit From: Verts
Random: off
Use Modifier Stack: on

  1. Set cache step: 1
  2. Bake the cache.
  3. A particle system is created as shown in the screen shot attached.

I assigned the same particle system to a cube that I duplicated from the original, unparenting from the empties and setting location keyframes on the object itself to get a similar motion to the original cube (bottom cube in screenshot). As you can see, the problem is only when the emitter is attached to an animated parent.

My system info:

Event Timeline

stephen thomas (stephenthomas0) raised the priority of this task from to Needs Triage by Developer.
Lukas Toenne (lukastoenne) triaged this task as Confirmed, Medium priority.May 2 2014, 9:11 AM

Looks like some kind of interpolation error (notice how it sort of deviates from the motion curve depending on the sub-frame). We've had similar issues relating to animated emitter parents, but this seems to be different (T39923: particle emitter not emitting in the same frequency when being parented to an empty, or object with rigid body dynamics. )

Fantastic. Thank you guys :)