Is there any API for query area in the world with a shape ?

sjinny · Post by **sjinny** » Sat Jun 02, 2007 7:32 am

Is there any API for query area in the world with a shape ?
for example, i use bullet in the server and use bullet's collision detection the find which objects would be seen by a client and i use an sphere to stand for a client's view.
how can i achieve this ?
thanks~

madMAx4 · Post by **madMAx4** » Sat Jun 02, 2007 9:10 am

therefor some engines have a volume sensor.
but there arent any sensors implemented in bullet yet as far as i know.

but you can send a few ray test around your sphere. this should work as long as your objects are not too small

sjinny · Post by **sjinny** » Sat Jun 02, 2007 1:27 pm

well....there would be too many rays in that way....

madMAx4 · Post by **madMAx4** » Sat Jun 02, 2007 1:42 pm

well i never tried this

you can take a look in OPAL's source code, there is a volume sensor implemented

link: http://ox.slug.louisville.edu/~o0lozi01 ... /Main_Page

Erwin Coumans · Post by **Erwin Coumans** » Sat Jun 02, 2007 2:25 pm

There are several ways to do this within Bullet. The Blender game engine allows to do such 'collision sensors'.

Two ways:
- Add a rigidbody/collision object with collision shape and disable the collision response:

Code: Select all

rbody->setCollisionFlags(rbody->getCollisionFlags() | btCollisionObject::CF_NO_CONTACT_RESPONSE);

Then check for contact points with this rigidbody (see CollisionInterfaceDemo how to find contacts) or add a collision callback for this object.

- Do a convex cast, this lets you find the first time of impact when moving an object along a path. This is similar to a raycast, but instead of a ray you can use a convex object (like sphere, box, cylinder etc). There is not a good interface in the btCollisionWorld at the moment, but it would be a small change to turn the raycast into an 'object cast'.

A good demo how to do this is lacking indeed, it would be useful to add this.
Thanks,
Erwin

Dragonlord · Post by **Dragonlord** » Sat Jun 02, 2007 2:32 pm

I didn't know this works in Bullet ( maybe the version I have is too old :O ). So far I did my own collision detection to do AI testing. So this convex casting gives you all the informations I need for my AI routines?
- Time To Impact
- Impact Normal
- Collision Response Callback ( to check if something can collide with each other )
- Hit Face ( so what triangle I hit in a mesh if a mesh is hit )

Erwin Coumans · Post by **Erwin Coumans** » Sat Jun 02, 2007 10:35 pm

I didn't know this works in Bullet ( maybe the version I have is too old :O ). So far I did my own collision detection to do AI testing. So this convex casting gives you all the informations I need for my AI routines?

Yes, this is all available in Bullet, but there is no easy interface for that. So for next version, I'll try to add a user-friendly interface for AI queries, with the following properties:

- Time To Impact

Yes

- Impact Normal

Yes

- Collision Response Callback ( to check if something can collide with each other )

Yes

- Hit Face ( so what triangle I hit in a mesh if a mesh is hit )

Yes

Hope this helps,
Erwin

Dragonlord · Post by **Dragonlord** » Sun Jun 03, 2007 1:29 am

Sounds good as my current AI testing code is more quick hack then optimized and doing this through Bullet should be speedier and making some lengthy code unneeded.