Bug in ComputeAllWorldSpaceBoundingBoxes

Development Asset Creation
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1

This function in BoundingVolumeUtilities.h has a bug:

template<typename ParticleView, typename T, int d>
typename TEnableIf<TModels_V<CParticleView, ParticleView>>::Type ComputeAllWorldSpaceBoundingBoxes(const ParticleView& Particles, const TArray<bool>& RequiresBounds, const bool bUseVelocity, const T Dt, TArray<TAABB<T, d>>& WorldSpaceBoxes)
{
	WorldSpaceBoxes.AddUninitialized(Particles.Num());
	ParticlesParallelFor(Particles, [&RequiresBounds, &WorldSpaceBoxes, bUseVelocity, Dt](const auto& Particle, int32 Index)
	{
		if (RequiresBounds[Index])
		{
			WorldSpaceBoxes[Index] = ComputeWorldSpaceBoundingBox(Particle);
			if (bUseVelocity)
			{
				if (const auto PBDRigid = Particle.AsDynamic())
				{
					WorldSpaceBoxes.Last().ThickenSymmetrically(ComputeBoundsThickness(*PBDRigid, Dt, 0, 1));
				}
			}
		}
	});
}

That final WorldSpaceBoxes.Last() should really be WorldSpaceBoxes[Index]. Notice you’re pre-allocating the array for the ParallelFor. I suspect this is a leftover from when this code wasn’t parallel, and it was adding the boxes sequentially into the array.

Ernesto.

2

Hello Ernesto,

Thank you for your report. Are you able to provide a description of the bug and what issues are caused by the current `ComputeAllWorldSpaceBoundingBoxes` implementation? This will assist us in identifying if it is necessary to put together a bug report for this. Thank you!

Take care,

John

3

I’m picking up this case where John left off, sorry for the delay. Confirming the bug with the Chaos team.

4

Yep, confirmed and your suggestion is correct. Merged in with CL 46769819 on //UE5/Main. Thanks for reporting this!

5

Hi John.

Unfortunately I don’t have a repro case at hand. I was tracking down the usage of ParticlesParallelFor() and spotted this bug.

The net effect of the bug is that anything that calls this function with bUseVelocity = true will not apply the ThickenSimmetrically() to the bounds of the particle, with the exception of the very last particle.

Ernesto.