Particle Collision failing in blender 2.80 #68128
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Reference: blender/blender#68128
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Blender Version
Broken: (example: 2.80rc1, 2.83
Worked: (optional) : 2.79b
Short description of error
My case is that when a collision object moves towards a bunch of particles which has zero velocity, in 2.79b the particles were ricocheted but in 2.80 they go straight.
Exact steps for others to reproduce the error
test_279.blend
Added subscriber: @sangwook71
Added subscriber: @JacquesLucke
I can confirm the issue, but it is unlikely that this is going to be fixed.. The current particle system is considered to be end-of-life.
Hmm... I think the problem doesn't belong to particle system, but belongs to collision system.
In 2.79 the collision works greatly!, but in advanced 2.8 version, it doesn't work correctly.
I think the new advanced version should include all of the prior version's functionalities except when there are some inevitable reasons that some functionalities should be excluded.
I discovered this error when I was following the Blender Guru tutorial (https:*www.blenderguru.com/), and the title is 'glass smashing (https:*www.youtube.com/watch?v=9L8qOq1Shiw&t=2096s)' which explains the glass shards tutorial using
collision system with particles.
Thank you !
Particle Collision Bugto Particle Collision failing in blender 2.80Added subscriber: @LucaRood-3
Added subscriber: @mano-wii
@LucaRood-3, shouldn't this problem have been solved by blender/blender-staging@0ef881cc57?
After investigating a little, I realized that the reason for the failure is the
Rigdy Body
.There is something wrong with updating the object's matrices in 2.80.
I suspect it is a lack of sync between the evaluated object and the original.
Added subscriber: @Sergey
After investigating, I realized that depsgraph calls 3 eval functions in a problematic order.
BKE_object_eval_local_transform
BKE_object_eval_uber_data
BKE_rigidbody_eval_simulation
BKE_rigidbody_eval_simulation
updatesob->obmat
according toRigid Body
simulation. Thisobmat
is that seen in the 3dview.BKE_object_eval_local_transform
takes values likeob->loc
,ob->rot
andob->scale
to updateob->obmat
, resetting it to the value beforeBKE_rigidbody_eval_simulation
.BKE_object_eval_uber_data
updates the collision modifier with the sameobmat
beforeBKE_rigidbody_eval_simulation
. (It is as if the object does not move).One solution would be to call
BKE_object_apply_mat4
and changeob->loc
,ob->rot
andob->scale
during theBKE_rigidbody_eval_simulation
. But I don't know if this is the most correct.BKE_object_eval_local_transform
should only be called at the end. No?@Sergey, would you have any light on this subject?
This is the same root issue as #58044. Will merge this report there.
Long story short: generally, rigid body needs to know object's geometry to have proper collision mesh, but geometry might need transform. In this case you're running into a feedback loop. There are ways to solve this, but all of them are rather big design changes.
See #58044 and the discussion in D6834 for more technical insights.
Closed as duplicate of #58044