collision detection


i have to animate falling bullets on a floor.
the bullets are actualy a jewelry object i did, so they
have other additions. my question is is it possible in blender
to calculate a perfect collision detection WITHOUT object intersections
and with proper object reflections?

i read someting about a script for the game engine to tunr things
there into ipos for blender but well i have NO clue how to use the
game engine at all!


From what I know about the game engine, its almost like the default settings simulate gravity. But, I am not to good in that area.

You could, however, use soft bodies. The floor or whatever would deflect and the bullets would have gravity. I cannot remember off the top of my head, but I think one of the sliders changes how rigid the object is. Just make it 100% rigid. It may take a while to compute, but then again maybe not because the bullets are not deforming like using a plane for cloth.


ok, i tried out using soft bodies for rigid stuff and, its not completely perfect but it may work depending.

maxing out espring and stiffquads you probably wont notive the “soft” effect. it seems to take longer to calculate though. i wouldn’t suggest for complex meshes.

you could make a bounding object with the soft settings applied (cube or rectangle) and make those the parents of the bullets/whatever. with some tweaking this may work.

haven’t tried making them collide with each other yet. I’ll get back to you on that.

heres a test anim, everything that moves is soft bodies, baked to make rendering faster. (with lots of stuff, this could get slow really fast so bake it so you don’t have to recalc all the time)

note, i can’t determine the source of the “flickering” on the extruded cube. it only shows when i compress the video to divx and doesn’t appear in the motion jpg avi or in the blend file.

with tweaking the results could look better than what i have.
you could build a simple counding object like the extruded cube and use that as the parent for your falling objects.

I’m game engine illiterate so i can’t help you on that side.



thats fun! now i found out how to do it on my own! the thing i cannot find out is how to prevent the cubes to intersect with each other.

i created another cube applied a deflector to it and parented it to a cube.
first the deflector cube did not fall down and second the falling cube inside somehow slips out of the deflector cube and was rotating like hell and than also third fall through the lower deflector plane. mhhh

any help???

this all works fine with subdiv. i extruded the deflector floor and applied an edge bevel and this slowed down the calculation a lot even while the ground object was not a subdiv object.


Hi Cekuhnen !

This is just an idea. I have not the time right now to makea trial :

What do you think about making two deflectors ?

  • The first deflector is the usual one. It is the floor mesh, used for gravity.

  • The second one could be a grid, extruded vertically in an array of square tubes. It is placed between the emitter plane that drops the dupliverted particles and the floor mesh.

When they fall down, the particles would follow the unvisible square tubes and do not collide each other ! Settings could be hard to avoid some jitter inside the tubes, because of the facing faces. The particles also may be automatically centered in the tubes by the reppellents forces…

I’ll try this as soon as I’ll have solved my problem with my winch animation !

Tell me if you try the trick… and if it works or not ! %|


Deflection code is very limited at the moment:

Deflectors won’t work properly when their vertices are moved by a ‘deform’ effect such as softbody, hooks, parented to armature.

The only way a deflector is ‘allowed’ to move is an object IPO. So i don’t see a way to get what you want with the current softbodies collision system.

Since realease is sheduled and a mayor rewiring is planned for the animation system after release, thoose issues will be in focus when animation system is back on its feet again.