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How Hdt Physics Extensions Works For Users (Please Correct Me If I'm Wrong) Now With Pictures


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This is not a guide or tutorial. Just information. I'm not an expert. I didnt make the plugin/mod. I just learnt this from reading about it on several different threads and from experience with using and tweaking it.


What is HDT physics Extensions?

HDT Physics Extensions is a plugin/mod for Skyrim that uses the havok engine and Skyrim script extender. To apply customizable physics to meshes including clothes, armors, hair, bodies etc. The customizations are based on a .xml file called HDTPhysicsExtensionsDefaultBBP.xml.


What are .xml files for HDT Physics Extensions?

.xml files are what HDT Physics Extensions use to determine how and what physics to apply to relevant meshes. The files themselves contain bone nodes and constraint information.

  • More about Bone nodes


Bone nodes are set places on a skeleton i.e left breast, left hand, right hand, right breast etc. The .xml file gives the Bone nodes weight, a shape(their hitbox) and tells them what to collide with. 

  • More on constraints


Constraints are how the nodes react to physics i.e how they bounce, jiggle etc.


How HDT Physics Extensions applies physics

Hdt Physics Extensions applies physics to meshes based on skeletal movement thats why more abrupt movement i.e jumping, crouching causes more bounce and jiggle etc. then what slight movements do. The skeletal movements are based on what animation is being played. If one of the meshes on a body i.e a body mesh, hands mesh or feet mesh is attached to a .xml. HDT Physics Extensions will also handle collisions of bone nodes. Based on the configurable shape of a bone node in the .xml. 


Why so many requirements?

HDT Physics Extensions requires SKSE, TBBP weighted meshes and a skeleton with the right bone nodes. It requires SKSE because it needs the extra scripts to apply physics( citation needed lol). It requires TBBP weighted meshes because they can have the physics applied to them because they are designed to move, bounce and jiggle etc. It requires a skeleton with the right nodes because if the skeleton didnt have the right nodes hdt physics extensions would be looking for nodes on the skeleton that didnt exist.


Whats the point of attaching .xml files to meshes/ whats the point of the havok object?

To enable collsions. Both do the same thing they add an item/mesh to the whole body i.e hair mesh, head mesh, body mesh, feet mesh, hands mesh and any item equipped. that tells hdt physics extension to apply physics to that body. If the .xml attached to either a mesh or the havok object has bone node collisions in it it will apply collisions to that complete body even though its just one item/mesh of the whole body.


Reason for making this thread

I noticed that quite a few people didnt understand how HDT physics works so I thought I would make a thread to both help myself get a better understanding of it through the knowledge of other people and more importantly to share my own knowledge about it. I've purposely tried to keep it as simple as possible so anyone can understand.


Well thats about it. If you survived that I hope you now have a better understanding of how HDT Physics Extension works and Thank you for taking the time to read this thread. I will update this when corrections are needed. Feel free to ask any questions you have and I'll try my best to answer them in an easy to understand way. Just remember though I'm not a modder, scripter, programmer etc. I'm just a somewhat normal dude who wants to share what he knows to help people understand better. 


Special thanks

Groovtama for his amazing skeleton

Stevierage for my favourite .xml

Blabba, clp2011 for their sage like tutorials

random others on the hdt physics extensions forum for the extra information


Thank you have a nice day!!!!

Having a nice day is not required. If having a shit day please see a doctor, seek nearest set of boobs/pecs (based on your own sexual preferences) or bottle of your favourite alcohol. Thank you

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If having a shit day please see a doctor, seek nearest set of boobs/pecs (based on your own sexual preferences) or bottle of your favourite alcohol. Thank you





Great Info. I had a basic understanding of HDT and this pretty much filled in the remaining holes. thanks alot.

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