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I am using Blender 2.71 and Python 3.4.0 and I would like to add a row of vertices in such a way that I can call them using bmesh.verts[] in the same order that I placed them (or in reverse).

I have placed them using the for loop:

for x in range (0,5):
    bmesh.verts.new((x,0,0))

This results in five vertices in a row starting from the origin. However, the call order for bm.verts[] is totally muddled. For example, if I then run the following:

bmesh.verts.remove(bm.verts[0])

the one that disappears is the second from the right. I would expect it to be either the left or right-most vertex. Can anyone explain to me which method Blender uses to store these vertices?

The object contains no other vertices.

I have noticed that when adding four or less the order is sequential from right to left, but something changes at five. Is this something to do with polygons?

Thanks

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Short answer is no, however...

BMesh only ensure vertices are added in-order when they are added to a newly created (or converted) mesh (which is OK for importers and geometry generators). Once vertices are removed you cant rely on this.

Best use a list of your own to keep a reference to vertices added if you need this.

Sorting

if your really need to ensure some order, you can sort verts using the same method used with Python lists eg:

bm.verts.sort(key=lambda v: v.co.x)

However it would be inefficient to sort vertices every time you add once.

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  • $\begingroup$ Thanks. What would you suggest to be the best way to reference the vertices? $\endgroup$
    – William
    Commented Aug 2, 2014 at 9:12
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    $\begingroup$ Ah, a "list" I suppose! $\endgroup$
    – William
    Commented Aug 2, 2014 at 9:21
  • $\begingroup$ Is there a way to create the vertex without using bmesh.verts.new(position)? I first tried to set the index immediately after creating a new vertex, and also tried implementing a list, however in both cases the new vertex is lost in amongst the muddled ordering before the reference can be applied, and I have to iterate through all the created vertices to find the new one (index=-1). There is a lot of excess computation as I am creating a terrain with many, many vertices. The only other thing I can think of is to use some function of the initial position as the index. Thanks for your help! $\endgroup$
    – William
    Commented Aug 2, 2014 at 11:02
  • $\begingroup$ Added note that you can sort bmesh vertices. but really you should add new vertices to a list if you care about order. $\endgroup$
    – ideasman42
    Commented Aug 2, 2014 at 11:37
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    $\begingroup$ I guess I will set the index/list reference by (co.y*rowsize + co.x) since it will be a rectangular grid. The reason I need to do this is to be able to use it like an topview image or heightmap for my terrain. I have some image processing experience and would like to apply the same morphology techniques to this project. $\endgroup$
    – William
    Commented Aug 2, 2014 at 12:06

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