Making sense of HDT-SMP: I just don't get it

[Doc_Ctdm]

Can someone please help me to understand HDT-SMP? More specifically:

- Does simply installing it increase processing demand significantly, or is something more required for the impact to occur?

- Is it always more demanding than the old HDT-PE, or is that only under certain conditions or circumstances?

- Is HDT-SMP backward compatible with PE XML files? Can old physics still be reused?

- What's the real difference between how the standard "HDT-SMP" CBBE body works vs. the 3BBB body version, from the standpoint of the physics system? How does SKSE "know" that the 3BBB body is different? Is it just the data in the XML, or are there additional definitions or triggers somewhere else too?

- Is there a similar distinction between HDT-SMP outfits that I don't realize? Do all "HDT-SMP" outfits have collision processing standard, or just some of them?  If an outfit or body isn't taking advantage of "Skinned Mesh Physics" then is it still called "HDT-SMP"?

 

[Mister X]

Heyho,

I'm definitely no pro in that topic, but I can try to explain what and how I understood so far (may be wrong though, too ?)

 

Does simply installing it increase processing demand significantly, or is something more required for the impact to occur?

Simply installing it, shouldn't be observable at processing demand, using it will be. As long as it's only used for jiggling of a few body regions or pieces it's ok, when there's collision or much stuff to calculate you may notice.

 

Is it always more demanding than the old HDT-PE, or is that only under certain conditions or circumstances?

Here I'm not sure. As for now I'd say SMP is a bit more demanding than PE, yet the source code of SMP got published so there will be development, PE is EOS as far as I know.

 

Is HDT-SMP backward compatible with PE XML files? Can old physics still be reused?

No, thery're not, it needs new ones. The advantage though is, that the ones of SMP are easier to interpret than the PE ones.

 

What's the real difference between how the standard "HDT-SMP" CBBE body works vs. the 3BBB body version, from the standpoint of the physics system? How does SKSE "know" that the 3BBB body is different? Is it just the data in the XML, or are there additional definitions or triggers somewhere else too?

Here I'm not sure again. AFAIK it's the way the area of physics calculation is applied to the body, together with a mixture of different physics calculation systems. 3BBB/3BA uses a mixture of SMP and CBPC for different body regions, where CBPC is way less demanding than any HDT calculation.

 

 Is there a similar distinction between HDT-SMP outfits that I don't realize? Do all "HDT-SMP" outfits have collision processing standard, or just some of them?  If an outfit or body isn't taking advantage of "Skinned Mesh Physics" then is it still called "HDT-SMP"?

If a body claims to have "HDT", be it PE or SMP, it should jiggle when you install SMP. The problem why some outfits won't lies deeper in the engine and the way SMP is applied to meshes. Basically spoken: any mesh has a name. SMP uses these names to know which calculation rules apply to which mesh. If an outfit mesh has the same name as the body mesh, both will jiggle the same way. If an outfit mesh uses another name than the body has, you will need a new ruleset for it to jiggle.

To explain how to change those names or define new rules will go too far now, for this you could ask here: