ConvexHull query in Collision Query Demo results in AccessViolationException

[Cray-1]

Hi, I tried to add a collision query with a convex hull. Seemed to work at first, but in some cases I get an AccessViolationException. I can reproduce this modifying the CollisionQueryDemo as follows:

1. Instead of the 5x5 box queries adding one (lines 224-238):

QuickList<Query> queries = new(1, BufferPool);
queries.Allocate(BufferPool) = new Query { Box = new Box(40, 15, 20), Pose = new RigidPose(new Vector3(0, 0.1f, 41), new Quaternion(-0.5f, -0.5f, -0.5f, 0.5f)) };

2. Increasing the size of queryWasTouched by one (line 241):
   BufferPool.Take(queries.Count + 1, out queryWasTouched);
3. Adding a ConvexHull query (line 249):

QuickList<Vector3> points = new QuickList<Vector3>(8, BufferPool);
points.AllocateUnsafely() = new Vector3(0, 0, 0);
points.AllocateUnsafely() = new Vector3(0, 0, 2);
points.AllocateUnsafely() = new Vector3(2, 0, 0);
points.AllocateUnsafely() = new Vector3(2, 0, 2);
points.AllocateUnsafely() = new Vector3(0, 2, 0);
points.AllocateUnsafely() = new Vector3(0, 2, 2);
points.AllocateUnsafely() = new Vector3(2, 2, 0);
points.AllocateUnsafely() = new Vector3(2, 2, 2);
AddQueryToBatch(new ConvexHull(points, BufferPool, out _), new Vector3(), queries.Count, ref collisionBatcher);

Am I creating the convex hull wrong or what else could be the problem?

[RossNordby]

I'm amazed this has never been hit before- shapes that get cached by the caller for tasks that generate child tasks got inappropriately returned to the pool early, potentially resulting in memory stomping if a later task used that same memory region.

Should be fixed in 1c4d1c5. Thanks for the report (again)!

[Cray-1]

Thanks for the quick reply (again) ;)
It indeed fixed the error of the reported example, but in a different case I get an AccessViolationException again. I don’t know if it is something similar or not and unfortunately the only way I could reproduce it in the Demo is by loading a static object from a file.
Therefore I added this simple function:

private Mesh ReadStl(string filepath, BufferPool bufferPool)
{
    BinaryReader reader = new(new FileStream(filepath, FileMode.Open, FileAccess.Read));
    reader.ReadBytes(80);
    int numTringles = reader.ReadInt32();
    bufferPool.Take<Triangle>(numTringles, out Buffer<Triangle> triangles);
    for (int triangleIndex = 0; triangleIndex < numTringles; triangleIndex++)
    {
        reader.ReadBytes(12);
        float x = reader.ReadSingle();
        float y = reader.ReadSingle();
        float z = reader.ReadSingle();
        Vector3 v1 = new(x, y, z);
        x = reader.ReadSingle();
        y = reader.ReadSingle();
        z = reader.ReadSingle();
        Vector3 v2 = new(x, y, z);
        x = reader.ReadSingle();
        y = reader.ReadSingle();
        z = reader.ReadSingle();
        Vector3 v3 = new(x, y, z);
        reader.ReadBytes(2);
        triangles[triangleIndex] = new Triangle(v1, v2, v3);
    }
    reader.Close();
    return new Mesh(triangles, new Vector3(1, 1, 1), bufferPool);
}

And loaded this mesh from the file as a static:
MeshException.zip

Mesh mesh = ReadStl("MeshException.stl", BufferPool);
Simulation.Statics.Add(new StaticDescription(new Vector3(), Simulation.Shapes.Add(mesh)));

Then this single box query results in the Exception during collisionBatcher.Flush()

queries.Allocate(BufferPool) = new Query { Box = new Box(105.905f, 193.368f, 126.943f), Pose = new RigidPose(new Vector3(300.3699f, 328.44067f, 430.81116f), new Quaternion(-0.1994829f, 0.1133757f, -0.35289928f, 0.9070913f)) };

It would be nice if you could look into this too.

[RossNordby]

Compound collision tests assume that there will be less than 262144 tests spawned by a single instance. The query overlaps more than that many triangles in the 350k triangle mesh, so that limit gets blown and bad stuff happens.

The bit packing is a little strained, so I'll probably first check if I can get away with widening the representation. Failing that, I can at least make the overflow not crash (though in that case, some child tests would be ignored).

[RossNordby]

New limit in aa6b0d8 is 2^20, and exceeding it is no longer fatal. Extra child pairs are ignored.

Could go higher than this, though there are some tradeoffs and even a million child pairs in a single top level pair is not exactly ideal for performance.

Thanks again!