AutoBone bone contribution fix & cleanup #552

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MrUnknownDE · 2026-04-05T19:42:40+02:00

MrUnknownDE commented

2026-04-05 19:42:40 +02:00

Originally created by @ButterscotchV on 11/23/2024

The bone contribution part of the AutoBone algorithm (getDotProductDiff()) seems to have been broken for a long time... Whoops! For this PR, I fixed contribution and ended up changing it to a metric that makes more sense. This is a fairly major change in the algorithm.

To explain bone contribution works, how this occured, and how this PR changes it:

Originally was to compare the difference in the direction the bone faces in regards to the direction of sliding between frames 1 and 2, this was to try to predict which bones could be causing sliding between two frames and by how much. This was flawed because it was just considering the direction the bone was facing and not really how it affected the tail position.
The bug was introduced in #787 by using the bone's global rotation separately from the transform offset, so it was not relative to any reasonable positioning and seems to have caused really poor results (I didn't think it would be any different as we only use the difference in the dot product, but I was wrong).
The way this PR implements this is:
- slideL/slideR = The difference in the global position of the ankle trackers between frames 1 and 2.
- boneOffL/boneOffR = The difference in the local tail positon of the bone (with rotation applied, this isolates the bone's effect on the skeleton) between frames 1 and 2.
- Compute the dot product between slide and boneOff as unit vectors, then apply that as a multiplier for the adjustment value. By computing the dot product between these values, we should get a vague estimate of exactly how much each bone is affecting the overall sliding and whether it needs to be shorter or longer. This sets a very clear target for the algorithm and guides it in its descent to the optimal proportions.
- Calculations are optimized by a minimum offset, values will not be computed if the offset is insignificantly small.

So far from my limited testing, this seems to make the algorithm perform significantly better. I also plan on working on a bit more cleanup of legacy code, but this is already pretty decent. Legacy code clean-up will be performed in a future PR in order to speed up code reviews.

*Originally created by @ButterscotchV on 11/23/2024* The bone contribution part of the AutoBone algorithm (`getDotProductDiff()`) seems to have been broken for a long time... Whoops! For this PR, I fixed contribution and ended up changing it to a metric that makes more sense. This is a fairly major change in the algorithm. To explain bone contribution works, how this occured, and how this PR changes it: 1. Originally was to compare the difference in the direction the bone faces in regards to the direction of sliding between frames 1 and 2, this was to try to predict which bones could be causing sliding between two frames and by how much. This was flawed because it was just considering the direction the bone was facing and not really how it affected the tail position. 2. The bug was introduced in #787 by using the bone's global rotation separately from the transform offset, so it was not relative to any reasonable positioning and seems to have caused really poor results (I didn't think it would be any different as we only use the difference in the dot product, but I was wrong). 3. The way this PR implements this is: - `slideL`/`slideR` = The difference in the global position of the ankle trackers between frames 1 and 2. - `boneOffL`/`boneOffR` = The difference in the local tail positon of the bone (with rotation applied, this isolates the bone's effect on the skeleton) between frames 1 and 2. - Compute the dot product between `slide` and `boneOff` as unit vectors, then apply that as a multiplier for the adjustment value. By computing the dot product between these values, we should get a vague estimate of exactly how much each bone is affecting the overall sliding and whether it needs to be shorter or longer. This sets a very clear target for the algorithm and guides it in its descent to the optimal proportions. - Calculations are optimized by a minimum offset, values will not be computed if the offset is insignificantly small. So far from my limited testing, this seems to make the algorithm perform *significantly* better. I also plan on working on a bit more cleanup of legacy code, but this is already pretty decent. Legacy code clean-up will be performed in a future PR in order to speed up code reviews.

MrUnknownDE closed this issue

2026-04-05 19:42:40 +02:00

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Reference: github/SlimeVR-Server#552