Mesh Boolean Difference failed

[WileyNg]

i have these two meshes and i tried to do a boolean difference operation from meshlib but it fails, giving me this error:

Bad contour on 4 mesh B faces, probably mesh A has self-intersections on contours lying on these faces.

MeshA is the shorter extrusion and MeshB is the taller extrusion.

Why did this happen?

this is how i am trying to call it.

    public static IntPtr BooleanDifference(IntPtr mrMeshA, IntPtr mrMeshB, out string error)
    {
        error = null;
        try
        {
            // Try with mergeAllNonIntersectingComponents = true
            var parameters = mrBooleanParametersNew();
            parameters.mergeAllNonIntersectingComponents = true;

            var result = mrBoolean(mrMeshA, mrMeshB, MRBooleanOperation.DifferenceAB, ref parameters);

            // CHECK ERROR STRING FIRST!
            if (result.errorString != IntPtr.Zero)
            {
                error = MRStringToString(result.errorString);
                mrStringFree(result.errorString);
            }

            if (result.mesh == IntPtr.Zero)
            {
                if (error == null) error = "Boolean operation returned null mesh";
                return IntPtr.Zero;
            }

            return result.mesh;
        }
        catch (Exception ex)
        {
            error = $"Exception: {ex.Message}";
            return IntPtr.Zero;
        }
    }      

MeshlibBooleanFailed.zip

[Grantim]

Hello!

There are several issues with this file:

1. Some triangles has inverted orientation which leads to non-manifoldness
2. There as extra faces present disconnected from main parts
3. Mesh A consists of several intersecting components - which leads to failed boolean

To perform A-B boolean you need fix mesh A (at in this case you need boolean unite components and might leave non-manifoldness as is beacuse they are not in meshB intersection zone but in general you should review meshA generation)

With fixed meshes boolean works as intended meshA - meshB.zip

---

The fix I did:

1. Separated loaded obj file to components

2. Removed 4 floating components

3. Inverted orientation of 3 non-manifold inverted components

4. Combined components from step 3 with their main components and called uniteCloseVertices

5. United two fixed MeshA components (from step 4) together (meshA.obj)

Then called boolean difference