Hi devs, I’m working on video tutorials for bmesh’s utilities and operators and got stuck on bmesh.utils.vert_collapse_faces. I’m facing few misunderstandings probably.

**Issue 1**

How is bmesh.utils.vert_collapse_faces different from bmesh.utils.vert_collapse_edge?

If I overlook the fact that vert_collapse_faces has two more parameters for now, what you see below is exactly the same result as with using vert_collapse_edge.

**Issue 2**

Documentation says “fac (float) – The factor to use when merging customdata [0 - 1]”

To test this parameter I assume that customdata is eg. vertex weights. Using the same example as above, I assigned weight=1 to all vertices except vert[0], which has weight=0.

My understanding is that if fac is:

0 then weight of vert[30] remains 1, original vert[0] has zero influence on vert[30]

1 then weight of vert[30] changes to 0 as original vert[0] has 100% influence on vert[30]

But I still get the same(original) value 1, whatever fac I set. Is it buggy or I’m getting it wrong?

**Issue 3**

Parameter join_faces isn’t documented.[Edit] - patch is here https://developer.blender.org/D9596

vert_collapse_faces works for me only if join_faces is set to **False**, using **True** I get

`ValueError: vert_collapse_faces(vert, edge): no new edge created, internal error`

Can you help me understand what it is suppose to do.

I checked github, blenderartists forums, bug tracker, addons bundled with Blender, but I couldn’t find a single example of how to use vert_collapse_faces properly.

Devs, pretty please, give me a hand.