Attaching extra information to a Scene Node

[itsagam]

What would be the best way to attach information to a scene node so I can extract it when I'm picking the scene node doing raycasting. I have an Enemy class that contains a reference to an AnimatedMeshSceneNode. So what would be the nicest way to get the reference to the Enemy class so that I can, say, deduct its health when I'm shooting at it.

[Granyte]

i just went through the same issue a couple of days ago and the only way of doing it was to write an interphase between a physic engine and irrlicht that would point to my data

an other way to do it when using only irrlicht would have been to derive custom classes from the diferent scene node class you need and have them point toward your custom data

[Brainsaw]

I use custom scene nodes for this issue. I got tons of those (with plugins for IrrEdit), and the integration is great (though it does increase the size of my scene files).

[greenya]

I would use some map, like:

Code: Select all

map<int, nodeAttachment>

And when you need to get node's custom data, you simply pick item from this map using node's id. Ofcause all nodes should have distinct id.

[CuteAlien]

Depending on the rest of the code you can maybe also use a map with <ISceneNode*, nodeAttachment>, which can be useful as the id is also needed for collision-groups (something I've run into in the past). Or you might abuse the "name" parameter - you can put a lot in a string.

[itsagam]

Thanks for the heads up! Sticking to custom scene nodes, I fear I might get into issues like managing IDs or housekeeping the map separately.

[itsagam]

@Brainsaw Can you post some code of a custom node scene node that addresses this? I'm doing it this way

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class EntitySceneNode : public ISceneNode
{
protected:
        aabbox3d<f32> Box;
        S3DVertex Vertices[4];
        SMaterial Material;
        
        void* userData;
public:
        EntitySceneNode(void* userData, ISceneNode* parent, ISceneManager* mgr, s32 id) : scene::ISceneNode(parent, mgr, id)
        {
                setUserData(userData);
        }
 
        virtual void render()
        {
        }
 
        virtual const core::aabbox3d<f32>& getBoundingBox() const
        {
                return Box;
        }
 
        virtual void setUserData(void* userData)
        {
                this->userData = userData;
        }
 
        virtual void* getUserData()
        {
                return userData;
        }
};

Code: Select all

        EntitySceneNode *entity = new EntitySceneNode(this, mapMesh, smgr, -1);
        mesh = smgr->addAnimatedMeshSceneNode(smgr->getMesh("./data/models/enemies/fatdude/fatdude.x"), 
                                mapMesh, 1, vector3df(0, 0, 0), vector3df(0, 0, 0), vector3df(0.3, 0.3, 0.3));
 

But it seems more like a hack than anything

[Brainsaw]

You could just take a look at my "ManagedShadowSceneNode" (http://bulletbyte.de/products.php?sub=i ... dowmanager). It is very simple, just adds a single integer as custom data (a level to define when a shadow should be added to an AnimatedMeshSceneNode which is this node's parent), it provides a shadow manager (singleton) that does the creation and removing. There also is a scenenodefactory and a plugin for IrrEdit so that I don't need to code this by hand. The package does also contain a small demo to show how it works. I hope you can get the necessary information from there, but feel free to ask if there are more questions.

[sudi]

Did anyone of you think about using a scenenode animator to hold userdata?

[CuteAlien]

Hm, advantage would be that it would allow adding a real custom object, but disadvantage is that it's update will be called each frame.

But shows more or less what a real custom-data would probably have to look like. Serializable custom objects.

[Brainsaw]

Did anyone of you think about using a scenenode animator to hold userdata?

I tried that, but I never go custom animators working in IrrEdit (which is a showstopper for me )

[sudi]

Did anyone of you think about using a scenenode animator to hold userdata?

I tried that, but I never go custom animators working in IrrEdit (which is a showstopper for me )

hmm ok i don't think i ever had that problem...besides there is still EditIrr somewhere^^

[Mel]

No, It has been a long time since i used Irredit for the last time... though i have my own custom editor, anyway...

The MOST risky way to have custom data attached to your scene nodes, though the simplest, is to hack directly the engine and add a public void* pointer to the ISceneNode class, recompile the engine, and acces that pointer like any other method or attribute of the ISceneNode class. That way, any the scene nodes could have any data attached to them and can be accessed inmediately, no need for searches nor anything. The bad thing is that it may break compatibility with other versions of the engine, but, customizing the engine maybe a need sometimes. But it is up to you.

Why Irrlicht doesn't have a void pointer in the scene nodes by default? it is useful to integrate Irrlicht with almost anything out there.

[serengeor]

Why Irrlicht doesn't have a void pointer in the scene nodes by default? it is useful to integrate Irrlicht with almost anything out there.

It might also work, by making ISceneNode inherit another class that would allow you to set some custom data. That would still need a recompile, but you then wouldn't have to rely on void pointers, I think. Don't really know how practical that would be, but it's an option.
Actually if you're not using irrlichts collision system to get nodes it is quite useless to have some other data attached to it from my point of view. Most of the times you would still write some sort of Object system that would allow you storing that information. I once used void pointers in bullet physics engine, but it is really dangerous as you mentioned. After that I changed it to work with bullets derived motion state class (a class that receives transformations of rigid body, used to update visual nodes) and that seemed to do the job quite better.

[CuteAlien]

Void pointers alone still are not sufficient as soon as you also want to support serialization of user data. In that case you need some custom userdata class and a way for users to add factories for those. That would be the clean solution. Which gets us back to the serialization system which is imho at the bottom of many problems right now.
Then again - adding a custom-data without serialization possibilities also has it's uses, leaving aside that it might be confusing as soon as we add a cleaner solution in the future. Personally I miss it a lot more in some gui-elements, where then again a void* pointer might not be optimimal but maybe rather some long int or similar (but not sure...). Actually at different times we already got 2 user-data values smuggeled in the engine (one in the IGUITable, the other somewhere in shaders) which as nothing ever was decided on how to implement that got implemented different (which might be ok or not).

Maybe we could name it something like runtime-user-data to make certain people realize it can't be used for serialization. And later on a clean solution. As it indeed makes coding just simpler in many cases I would be fine with that, but I won't add it without consent of other engine-coders as I know that especially Niko was a lot against adding user-data in the past.

Or maybe someone starts thinking up a clean solution for our serialization system which (beside other features) allows adding serializable custom structures in an easy way. Or any other idea... (just noting that in the past I also simply wanted to add a void* until I got some explanation why this is not optimial).