Rigid body dynamics: Initially deactivated objects are not activated on collision, but on bounding box intersection
Open, ConfirmedPublic


System Information
MacOS 10.12.3

Blender Version
Broken: 2.78 2017-02-23

Short description of error
When setting the rigid body dynamics of an object so that "Enable Deactivation" and "Start Deactivated" are both enabled, the expected result is that the object is "activated on collision with other objects" (quote from the manual). Instead, the object is already activated when its bounding box and another active and dynamic rigid body object's bounding box intersect, even if the two objects never collide.

Exact steps for others to reproduce the error
Open the attached .blend, then start the animation (Alt-A or click on play) and watch closely at what point the capital T is activated (it starts falling down).
Alternatively, there are two small spheres behind the text. The top sphere is deactivated, but the bottom one immediately activates it even though they don't collide.



I confirm the problem with master hash d66d579 on ubuntu 16.04 64 bits.

Luca Rood (LucaRood) triaged this task as "Confirmed" priority.Mar 10 2017, 8:26 AM

At first glance, this seems like a bug in Bullet. As far as I can tell from a quick look, this wrong activation isn't triggered by any of Blender's activation calls, so it is probably Bullet activating the object on its own will...

Anyway, I'll try to have a more thorough look at this when I have some time.
In the meantime, if anyone wants to, feel free to tackle this though...
Btw, @Alexander Gavrilov (angavrilov) and @Martin Felke (scorpion81), this might interest you.

This is not really a bug but more of a limitation.
I have a patch that does proper deactivation in the rigid body improvements branch, but it wasn't committed because it wasn't clear how deactivation should be handled in blender in general.
I might dust if off since this really can be preveived as a bug.