Select next and previous edge in a loop for selected edge

Question

Need a help to select next and previous edge in a loop for selected edge. This do not work for me properly:

import bpy
import bmesh
me = bpy.context.object.data
bm = bmesh.from_edit_mesh(me)
Get the selected edge
selected_edges = [e for e in bm.edges if e.select]
Get the first selected edge (assuming only one is selected)
selected_edge = selected_edges[0]
bpy.ops.mesh.loop_multi_select(ring=False)
Find the edge loop
edge_loop = [e for e in bm.edges if e.select]
bpy.ops.mesh.select_all(action='DESELECT')
Select the next and previous edges in the loop
index = edge_loop.index(selected_edge)
prev_edge = edge_loop[(index - 1) % len(edge_loop)]
next_edge = edge_loop[(index + 1) % len(edge_loop)]
selected_edge.select = True
prev_edge.select = True
next_edge.select = True
bmesh.update_edit_mesh(me)

This also do not work properly:

import bpy
import bmesh
me = bpy.context.object.data
bm = bmesh.from_edit_mesh(me)
edges = [e for e in bm.edges if e.select]
for e in edges:
    for loop in e.link_loops:
        loop.link_loop_prev.link_loop_radial_prev.link_loop_prev.edge.select = True
bmesh.update_edit_mesh(me)

X Y · Accepted Answer · 2023-10-31T13:04:52.490

According BMesh get edge loop:

One direction

import bpy
import bmesh
Edit mode require....
me = bpy.context.object.data
bm = bmesh.from_edit_mesh(me)
Get the selected edge
selected_edges = [e for e in bm.edges if e.select]
Get the first selected edge (assuming only one is selected)
selected_edge = selected_edges[0]
for loop in selected_edge.link_loops:
    if len(loop.vert.link_edges) == 4:
        break
while len(loop.vert.link_edges) == 4:
    # jump between BMLoops to the next BMLoop we need
    loop = loop.link_loop_prev.link_loop_radial_prev.link_loop_prev
loop.edge.select_set(True)
# following edge in the edge loop
e_next = loop.edge


bmesh.update_edit_mesh(me)

Both direction

import bpy
import bmesh
Edit mode require....
me = bpy.context.object.data
bm = bmesh.from_edit_mesh(me)
Get the selected edge
selected_edges = [e for e in bm.edges if e.select]
Get the first selected edge (assuming only one is selected)
selected_edge = selected_edges[0]
_temp = None
for loop in selected_edge.link_loops:
    if len(loop.vert.link_edges) == 4:
        _temp = loop
        break
while len(loop.vert.link_edges) == 4:
    # jump between BMLoops to the next BMLoop we need
    loop = loop.link_loop_prev.link_loop_radial_prev.link_loop_prev
loop.edge.select_set(True)
# following edge in the edge loop
e_next = loop.edge


if _temp is not None:
    for loop in selected_edge.link_loops:
        if loop != _temp and len(loop.vert.link_edges) == 4:
            break
while len(loop.vert.link_edges) == 4:
    # jump between BMLoops to the next BMLoop we need
    loop = loop.link_loop_prev.link_loop_radial_prev.link_loop_prev

    loop.edge.select_set(True)
    # following edge in the edge loop
    e_next = loop.edge


bmesh.update_edit_mesh(me)

Updated: Both cases, 3 edges only

import bpy
import bmesh
Edit mode require....
me = bpy.context.object.data
bm = bmesh.from_edit_mesh(me)
Get the selected edge
selected_edges = [e for e in bm.edges if e.select]
Get the first selected edge (assuming only one is selected)
selected_edge = selected_edges[0]
_temp = 0
if len(selected_edge.link_loops) == 1:
    # case border
    for loop in selected_edge.link_loops:
        e0 = loop.link_loop_prev.edge
        e1 = loop.link_loop_next.edge
_set = {selected_edge, e0, e1}

for v in selected_edge.verts:
    for edge in v.link_edges:
        if edge not in _set:
            edge.select_set(True)
            break

else:
    # case inside
    for loop in selected_edge.link_loops:
        if len(loop.vert.link_edges) == 4:
            loop.link_loop_prev.link_loop_radial_prev.link_loop_prev.edge.select_set(True)
            _temp += 1
        if _temp == 2: break
bmesh.update_edit_mesh(me)

Get 2 connected edges based on the maximum angle

import bpy, bmesh
from mathutils import Vector
Return the 2 edges with the maximum intersection angle
def get_2_side_edges(edge):
    v0, v1 = edge.verts
    vec = v1.co - v0.co
    if vec.length == 0:
        return None, None
best_angle = 0.0
best_edge0 = None

for e in v0.link_edges:
    if e == edge: continue
    verts = e.verts
    an = (verts[0].co - verts[1].co).angle(vec, None)

    if an != None and an &gt; best_angle:
        best_angle = an
        best_edge0 = e

best_angle = 0.0
best_edge1 = None

for e in v1.link_edges:
    if e == edge: continue
    verts = e.verts
    an = (verts[0].co - verts[1].co).angle(vec, None)

    if an != None and an &gt; best_angle:
        best_angle = an
        best_edge1 = e

return best_edge0, best_edge1



me = bpy.context.object.data
bm = bmesh.from_edit_mesh(me)
need 1 edge that selected
e = [e for e in bm.edges if e.select][0]
e0, e1 = get_2_side_edges(e)
if e0 != None: e0.select_set(True)
if e1 != None: e1.select_set(True)
bmesh.update_edit_mesh(me)
bm.free()

Priority version

import bpy, bmesh
from mathutils import Vector
Return the 2 edges with the maximum intersection angle
def get_2_side_edges(edge, priority=None):
    v0, v1 = edge.verts
    vec = v1.co - v0.co
    if vec.length == 0:
        return None, None
def get_best_angle_edge(edges):
    best_angle = 0.0
    best_edge0 = None

    for e in edges:
        if e == edge: continue
        verts = e.verts
        an = (verts[0].co - verts[1].co).angle(vec, None)

        if an != None and an &gt; best_angle:
            best_angle = an
            best_edge0 = e
        return best_edge0


if priority == &quot;unshared_face&quot;:
    # check if unshared_face exists
    edge_link_faces = edge.link_faces
    exclude_edges = set()
    for f in edge_link_faces:
        exclude_edges.update(f.edges)

    edges0 = [e for e in v0.link_edges if e != edge and e not in exclude_edges]
    edges1 = [e for e in v1.link_edges if e != edge and e not in exclude_edges]
    print(len(edges0), len(edges1))
    if not edges0: edges0 = v0.link_edges
    if not edges1: edges1 = v1.link_edges
else:
    edges0 = v0.link_edges
    edges1 = v1.link_edges

return get_best_angle_edge(edges0), get_best_angle_edge(edges1)




me = bpy.context.object.data
bm = bmesh.from_edit_mesh(me)
need 1 edge that selected
e = [e for e in bm.edges if e.select][0]
e0, e1 = get_2_side_edges(e, priority="unshared_face")
if e0 != None: e0.select_set(True)
if e1 != None: e1.select_set(True)
bmesh.update_edit_mesh(me)
bm.free()

I need total 3 edges selected: original one, next and previous in a loop — APEC, Oct 29 '23 at 18:30
Yes it work but only for inside selected edge. For Case like on my second screen (some border edge selected) it do not add selection — APEC, Oct 29 '23 at 18:42
Yes, the border edge case does not work, the new one should work on both case. — X Y, Oct 29 '23 at 19:14
New Case if selected edge is near n-gon, so from one side good quads and from other side n-gone. After selecting edge between this sides and using last code nothing happen — APEC, Oct 30 '23 at 08:06
For the case without edge loops,, you can calculate both sides based on the intersection angle, I provided a new one. — X Y, Oct 30 '23 at 22:43
new case found: if select edge perpendicular to hard angle side https://i.imgur.com/aK2xll5.png In my situation I have no such surface, but still interesting note — APEC, Oct 31 '23 at 11:04
This is normal behavior because the 3 edges intersect at the same 90 degree angle. The idea is to check if edges have shared faces. See the new one. — X Y, Oct 31 '23 at 13:08
If there are no faces, you can compare the edge directions and see which one is not similar, but you need to do this yourself. — X Y, Oct 31 '23 at 13:18

score 0 · Answer 2 · answered Oct 29 '23 at 18:03

Temporary solution using dictionary to combine edges and their verts and find other edges contained vertex from selected edge... But I think its a very resource and time consuming operation.

import bpy
import bmesh
obj = bpy.context.active_object
bm = bmesh.from_edit_mesh(obj.data)
selected_edges = [e for e in bm.edges if e.select]
for e in selected_edges:
    edge_verts = {}
    bpy.ops.mesh.select_all(action='DESELECT')
    e.select = True
    bpy.ops.mesh.loop_multi_select(ring=False)
    selected_loop = [e for e in bm.edges if e.select]
for edge in selected_loop:
    verts = [v for v in edge.verts if v.select]
    edge_verts[edge] = verts

p = [v for v in e.verts]
other = [edge_index for edge_index, vert_index in edge_verts.items() if vert_index[0] in p or vert_index[1] in p]

bpy.ops.mesh.select_all(action='DESELECT')
for e in other:
    e.select = True

Select next and previous edge in a loop for selected edge

Get the selected edge

Get the first selected edge (assuming only one is selected)

Find the edge loop

Select the next and previous edges in the loop

2 Answers2

Edit mode require....

Get the selected edge

Get the first selected edge (assuming only one is selected)

Edit mode require....

Get the selected edge

Get the first selected edge (assuming only one is selected)

Edit mode require....

Get the selected edge

Get the first selected edge (assuming only one is selected)

Get 2 connected edges based on the maximum angle

Return the 2 edges with the maximum intersection angle

need 1 edge that selected

Priority version

Return the 2 edges with the maximum intersection angle

need 1 edge that selected