Fix T78406: create uv randomize islands operator

Implement a new operator to randomize the scale, rotation and offset
of selected UV islands.

release/scripts/modules/bpy_extras/bmesh_utils.py

@@ -0,0 +1,58 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+__all__ = (
+    "bmesh_linked_uv_islands",
+)
+
+import bmesh
+
+def match_uv(face, vert, uv, uv_layer):
+    for loop in face.loops:
+        if loop.vert == vert:
+            return uv == loop[uv_layer].uv
+    return False
+
+
+def bmesh_linked_uv_islands(bm, uv_layer):
+    """
+    Returns lists of face indices connected by UV islands.
+
+    For `bpy.types.Mesh`, use `mesh_linked_uv_islands` instead.
+
+    :arg bm: the bmesh used to group with.
+    :type bmesh: :class: `BMesh`
+    :arg uv_layer: the UV layer to source UVs from.
+    :type bmesh: :class: `BMLayerItem`
+    :return: list of lists containing polygon indices
+    :rtype: list
+    """
+
+    result = []
+    bm.faces.ensure_lookup_table()
+
+    used = {}
+    for seed_face in bm.faces:
+        seed_index = seed_face.index
+        if used.get(seed_index):
+            continue # Face has already been processed.
+        used[seed_index] = True
+        island = [seed_index]
+        stack = [seed_face] # Faces still to consider on this island.
+        while stack:
+            current_face = stack.pop()
+            for loop in current_face.loops:
+                v = loop.vert
+                uv = loop[uv_layer].uv
+                for f in v.link_faces:
+                    if used.get(f.index):
+                        continue
+                    if not match_uv(f, v, uv, uv_layer):
+                        continue
+
+                    # `f` is part of island, add to island and stack
+                    used[f.index] = True
+                    island.append(f.index)
+                    stack.append(f)
+        result.append(island)
+
+    return result