Why won't some triangles convert to quads?

Right now I selected to adjacent triangles and hit alt + J. Nothing. I try doing it throught the spacebar and… nothing. Then I delete the edge that is part of both triangles, select the 4 vertex and make the face. That works.

The thing is that it failed once, then I wanted to make another 2 tri into a quad, and it worked. Then tried again and failed. Any conditions the 2 triangles have to meet in order for a successful convert to quad?

I have noticed this behavior as well. One thing that I have found that sometimes helps is to “xsort” the mesh (found under mesh tools). This also sometimes helps on occasions when pressing F has trouble creating quads.

Hope this helps
GreyBeard

first, are you sure it is two triangles?

second, they have to be more-or-less planar and have the nomals pointing about the same way

turn off double sided in the edit buttons, if one of the triangles is black that is your problem

if your triangles form a crecent shape, it is also a possiblity they will not be converted to a quiad (it isn’t a good idea to expect it to happen in the first place)

Honestly I think it’s something with the code. Some sort of bug that goes undetected.

Exactly now I tried to convert a 2 tri to a quad. Yep I’m sure they are two triangles. The normals are almost parallel.

I don’t know what a crecent shape it :frowning:

I noticed that sometimes when you can’t make a quad, and you make a quad from 4 vertex into a face directly, many times the ‘face’ is something really twisted. I remember having this problem with quads since my first times with blender long long time ago… %|

EDIT: Okay I just discovered something. The shape of the surrounding faces to the triangles you want to convert to a quad also play a role in this, so if the surrounding face is a quad, and has a V shape, I mean non-planar, it would give weird results.

Me gonna try deleting ugly V shaped face now. Me try making 2 nice triangles before restoring ugly V face.

EDIT2: Deleting ugly V shaped face before making nice triangles a quad worked ^.^ Me happy. :smiley:

Yeah I know it’s stupid talking like that. Bite me. :wink: And thanks

Honestly I think it’s something with the code. Some sort of bug that goes undetected.

Just old code. There’s help on the way though:

From:
http://www.blender.org/modules.php?op=modload&name=phpBB2&file=viewtopic&t=3806

Second major improvement involves the calculation of correct splitted
triangles, when a quad is not flat. It now creates triangles based on the
vertex normals, which have actual information on surrounding geometry, thus
resulting in much smoother results.
Without this you get errors in ray-shadow, with light shining almost
parallel to a face. But again, displacement mapping improves with it too.

%<

Crescent shape looks kind of like this: <