Collision models

[Baal]

I need a bit of clarification on the subject of collision models, clip models, trace models and collision detection. I was browsing the source but that's time consuming and I am now heavily confused. So I'll just ask some (hopefully not to stupid) questions.

 

There are some models that need a collision model to be used as moveables. If a model contains such a collision model is this also used on static objects?

What kind of control has a mapper over this?

Do projectiles (arrows) collide with the render model or the collision model?

What about blocking of AI vision?

 

SDK related questions:

There is a so called trace model that's restricted to a few vertices. I guess this is the collision model used on non static objects for efficiency.

How are clip and trace model actually related?

[Springheel]

There are some models that need a collision model to be used as moveables. If a model contains such a collision model is this also used on static objects?

 

Yes. This is a bit unfortunate, as it means that you can't drop things into a static bucket, since the bucket model is also used as a movable and thus has a collision mesh which blocks the top. It also creates problems with chairs.

 

What kind of control has a mapper over this?

 

Not much.

 

Do projectiles (arrows) collide with the render model or the collision model?

 

If it has a collision model then arrows collide with that. If it doesn't, then it uses the render model.

 

What about blocking of AI vision?

 

Hmm, that's a good question. Though in most cases the collision model is about the same size as the visual model, so it shouldn't matter too much in practice.

[greebo]

SDK related questions:

There is a so called trace model that's restricted to a few vertices. I guess this is the collision model used on non static objects for efficiency.

Yes, it's the tracemodel is used by the closed source CollisionModelManager to detect collisions.

 

How are clip and trace model actually related?

I'm only 99% sure so take this with some scepticism.

 

You can regard the idClipModel as some sort of "middleman" between idEntity/idPhysics and the collisionmodel manager. In fact, the idClipModel/idClip classes are using idTraceModels as helper. The tracemodels are strictly mathematical class containing only the info needed to detect collisions (edges, vertices, polies, etc.), whereas the Clipmodel class is also containing gameplay info like body index, pointers to their owning entities, bounds and an entire tracemodel allocation cache.

 

idPhysics make use of idClipModel and idClip to query collisions (and other stuff btw), which in turn are passing their idTraceModels to the idCollisionManager.

 

Does this help?

[Springheel]

There are some models that need a collision model to be used as moveables. If a model contains such a collision model is this also used on static objects?

 

Yes. This is a bit unfortunate, as it means that you can't drop things into a static bucket, since the bucket model is also used as a movable and thus has a collision mesh which blocks the top. It also creates problems with chairs.

 

Incidently, this is why I prefer making the CM in a modelling program so that it can fit the shape of the visible mesh as closely as possible, rather than using DR to make one.

[Baal]

Does this help?

I was asking out of curiousity mainly but, yes, thank you.

 

you can't drop things into a static bucket, since the bucket model is also used as a movable and thus has a collision mesh which blocks the top

But you could disable the model with "noclipmodel" on a static bucket, right? And there's also the "clipmodel" key through wich you can assign a different cm. And, if I'm correct, that isn't as restricted for non movebales.

[Springheel]

But you could disable the model with "noclipmodel" on a static bucket, right

 

Oh really? I wasn't aware of that. What do you do, add "noclipmodel" "1" in the entity window?

[Baal]

add "noclipmodel" "1" in the entity window?

Yes, I think so. If you do that it will load the rendermodel as the clip model. For static objects that could be possible.

[greebo]

"noclipmodel" "1" will render the entity completely nonsolid, i.e. arrows or the player will run right through. When this is set to "1" the code will not load any clipmodel, unless you specify one using the "clipmodel" spawnarg.