Getting the correct brush size for trigger.

[reepblue]

Hey all,

 

I've created a trigger class that on touch stores the entity in a list, and checks a listed entity left the bounds in UpdatePhysics. The code I have works fine, but I'm running into an issue that it seems that the extra padding for brushes are causing incorrect values. The entity has to leave the volume, plus a few centimeters for the onendTouch function to be called.

 

Here is the UpdatePhysics code.

 

void SimpleTrigger::UpdatePhysics()

{

if (!m_bEnabled)

return;

 

if (!m_bHadCollision)

return;

 

if (m_hTouchingEntities.size() <= 0)

return;

 

list<Entity*>::iterator iter = m_hTouchingEntities.begin();

for (iter; iter != m_hTouchingEntities.end(); iter++)

{

// zentity is the entity where looking for.

Entity* zentity = *iter;

if (zentity)

{

if (entity->GetDistance(zentity) > entity->GetAABB(Entity::GlobalAABB).size)

{

onendTouch(zentity);

break;

}

}

}

 

While this works really well, again, I think the extra AABB padding is getting in the way. I also feel that the for loop is a bit over the top/expensive way of doing this. Any help to make this work better would be appreciated!

 

Thanks.

[nick.ace]

Isn't the AABB box supposed to not be used for collisions? There's nothing really you can do about that. Personally, I would just use collisions for triggers. Otherwise, use some quick rectangular prism intersection test.

 

In terms of the loop efficiency, it's hard to determine whether that would be a good setup or not depending on the application. But there are probably better techniques to use. You could use a KD-tree so that you don't need to test every entity. IDK how costly it is to set up each frame compared to your list approach though. I wouldn't use the "list" data structure. Use "vector" instead if you are going to use a list like you are using. With "list" you are going to be building a chain of pointers, so you will have fragmented memory and get more cache misses, so your loop will be less efficient.

 

Also, I would avoid using GetDistance() and just square the second term. Implement your own distance function without the use of square-root.

[reepblue]

I do use the collision hook for adding objects to the touch list. It's removing the object from the volume is my issue. I tried the Enter/Exit trigger script on the old wiki, but it only detects if all objects are out.

 

I'm also using list because vector doesn't seem to have a way or removing an object from it.

[nick.ace]

Ah ok, I didn't know there were no hooks or anything for leaving an entity. Why not program a box intersection test yourself though? Then you'd have as much control as you would need. You would need to scan through all entities at startup and then calculate the highest +x, -x, +y -y, +z, and -z values for the vertices of a mesh.

 

You can remove elements from a vector. You should just swap the element you want to remove with the last element and use pop_back(). Don't use the erase() method though. A vector is just an array behind the scenes whereas a list is not.