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Improve heightfield collision performance #3276

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glebm opened this issue Feb 21, 2021 · 2 comments
Closed

Improve heightfield collision performance #3276

glebm opened this issue Feb 21, 2021 · 2 comments

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@glebm
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glebm commented Feb 21, 2021 •
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In openmw, btHeightfieldTerrainShape::processAllTriangles is 15% of the total frame time

perf report showing heighfield collision taking a significant amount of time in openmw

I've noticed the following TODO in the code that points to the possibility of optimizing this:

bullet3/src/BulletCollision/CollisionShapes/btHeightfieldTerrainShape.cpp

Line 336 in abea1a8

// TODO If m_vboundsGrid is available, use it to determine if we really need to process this area

Heightfield accelerator data structure (m_vboundsGrid) was introduced in #2062

There are a few other TODOs in the file that also indicate missing optimizations.

Update: No longer a bottleneck even without the accelerator thanks to #3287. Leaving open for now in case someone wants to do address the TODOs and claim the bounty.

/cc @Zylann @psi29a
@glebm
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glebm commented Feb 26, 2021

Posted a bounty https://www.bountysource.com/issues/96668355-heighfield-collision-performance

@glebm glebm changed the title Heighfield collision performance Improve heighfield collision performance Feb 26, 2021
@glebm glebm changed the title Improve heighfield collision performance Improve heightfield collision performance Feb 26, 2021
psi29a pushed a commit to OpenMW/openmw that referenced this issue Feb 26, 2021
@glebm
heighfield: buildAccellerator()
21a70b7 
This enables accelleration of heightfield collisions.

Unfortunately, `btHeightfieldTerrainShape::processAllTriangle` does not
yet use the accellerator data, so this change does not improve
performance yet but might do so in future bullet versions.

References:

* Accellerator introduced in:
  bulletphysics/bullet3#2062

* Feature request to use the accellerator in `processAllTriangle`:
  bulletphysics/bullet3#3276
@glebm glebm mentioned this issue Feb 28, 2021
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@glebm
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glebm commented Mar 1, 2021

After #2062, in areas where heightfield collision is still slow, perf report looks like this:

perf report showing most time spent in btGjkPairDetector::getClosestPointsNonVirtual

@bulletphysics bulletphysics locked and limited conversation to collaborators Apr 26, 2021

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@glebm @erwincoumans