Rig weld: decide weld pairs once at rest pose (per avatar, on outfit/shape/LOD change); per-frame pass only averages the pairs

sky_line commented

2026-10-10 12:06:02 +00:00

Owner

Idea (owner, 2026-10-10)

Decide rigged-mesh weld pairs once, at the avatar's rest pose, and apply them cheaply every frame. Today the weld rediscovers the same pairs every frame.

Today

clean_rig_weld.comp / llcleanrigweldvk.cpp runs after pre-skin every frame:

Hash ~43k boundary vertices by skinned position (boundary vertices live 42951).
Search neighbouring cells for vertices of other meshes of the same avatar within RenderVKRigWeldDistance (0.2 mm).
Average the matches.

Steps 1-2 are most of c_rigweld (~0.5-0.7 ms in a ~62-avatar crowd).

Do

Pair discovery, once per avatar: skin each rigged mesh with the bind/rest pose including the avatar's shape (fitted mesh / collision volumes / joint offsets), on the GPU. Find cross-mesh boundary pairs within the weld distance. Apply the #626 rule: only pair vertices whose skin weights are similar (same dominant joints, weights within a tolerance), so cavities and onion-skin layers aren't welded. Store a compact per-avatar pair list (vertex index pairs + mesh ids).
Per frame: a tiny gather pass after pre-skin averages each pair's position (and normal) from the skinned output. No hashing, no search. Expected ~0.05-0.1 ms for the same vertex count.
Recompute asynchronously only on: attach/detach, wearable/outfit change, appearance/shape change, rigged LOD switch (#561/#612), rig weld setting changes. Until the new list is ready, keep the old one or skip welding; never stall.
Keep meshes separate. Merging gives no per-mesh saving: draws are GPU MDI with per-face materials, pre-skin and refit are per-vertex, RT is already grouped. It would also break per-attachment hide/LOD/alpha/detach.

Behaviour change

Pairs are fixed by how meshes meet at rest instead of per pose. Real seams (neck/head, wrists/hands, clothing edges) meet at rest and stay joined. Accidental pose-dependent welds go away.

Measure

c_rigweld before/after in the same crowd; pair count and recompute count/time in the VKRigWeld log line. Visual: neck/wrist seams under animation, cavities (mouths, pockets), layered clothing.

Absorbs #626 (weight-based weld). Related: #574, #632.

## Idea (owner, 2026-10-10) Decide rigged-mesh weld pairs **once**, at the avatar's rest pose, and apply them cheaply every frame. Today the weld rediscovers the same pairs every frame. ## Today `clean_rig_weld.comp` / `llcleanrigweldvk.cpp` runs after pre-skin every frame: 1. Hash ~43k boundary vertices by skinned position (`boundary vertices live 42951`). 2. Search neighbouring cells for vertices of *other* meshes of the same avatar within `RenderVKRigWeldDistance` (0.2 mm). 3. Average the matches. Steps 1-2 are most of `c_rigweld` (~0.5-0.7 ms in a ~62-avatar crowd). ## Do 1. **Pair discovery, once per avatar:** skin each rigged mesh with the bind/rest pose *including the avatar's shape* (fitted mesh / collision volumes / joint offsets), on the GPU. Find cross-mesh boundary pairs within the weld distance. Apply the #626 rule: only pair vertices whose skin weights are similar (same dominant joints, weights within a tolerance), so cavities and onion-skin layers aren't welded. Store a compact per-avatar pair list (vertex index pairs + mesh ids). 2. **Per frame:** a tiny gather pass after pre-skin averages each pair's position (and normal) from the skinned output. No hashing, no search. Expected ~0.05-0.1 ms for the same vertex count. 3. **Recompute** asynchronously only on: attach/detach, wearable/outfit change, appearance/shape change, rigged LOD switch (#561/#612), rig weld setting changes. Until the new list is ready, keep the old one or skip welding; never stall. 4. **Keep meshes separate.** Merging gives no per-mesh saving: draws are GPU MDI with per-face materials, pre-skin and refit are per-vertex, RT is already grouped. It would also break per-attachment hide/LOD/alpha/detach. ## Behaviour change Pairs are fixed by how meshes meet at rest instead of per pose. Real seams (neck/head, wrists/hands, clothing edges) meet at rest and stay joined. Accidental pose-dependent welds go away. ## Measure `c_rigweld` before/after in the same crowd; pair count and recompute count/time in the VKRigWeld log line. Visual: neck/wrist seams under animation, cavities (mouths, pockets), layered clothing. Absorbs #626 (weight-based weld). Related: #574, #632.

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2026-10-10 12:06:02 +00:00

sky_line added this to the Slipstream project

2026-10-10 12:06:02 +00:00

sky_line referenced this issue

2026-10-10 12:06:02 +00:00

Make held animation frames free: skip pre-skin / weld / BLAS refit for avatars whose pose was not re-evaluated (pelvis-local pre-skin) #632

sky_line referenced this issue