feat: Add mirror mesh tool

.vscode/settings.json

@@ -1,3 +1 @@
-{
-  "python.analysis.typeCheckingMode": "basic"
-}
+{}

pyproject.toml

@@ -5,10 +5,11 @@ description = "Add your description here"
 readme = "README.md"
 authors = [{ name = "Yuki Kitagawa", email = "yuki.kitagawa@pm.me" }]
 requires-python = ">=3.11,<3.12"
-dependencies = [
-    "fake-bpy-module-latest>=20250505",
-]
+dependencies = ["fake-bpy-module-latest>=20250505"]
 
 [build-system]
 requires = ["hatchling"]
 build-backend = "hatchling.build"
+
+[tool.pyright]
+reportInvalidTypeForm = false

src/solstice/__init__.py

@@ -11,7 +11,7 @@ bl_info = {
 # Test if the libraries are already loaded
 # This is useful for reloading the addon during development
 
-if "solstice.align_island" in sys.modules:
+if any(map(lambda x: x.startswith("solstice."), sys.modules.keys())):
     # Purge any existing modules with 'solstice.' prefix
     for module_name in list(sys.modules.keys()):
         if module_name.startswith("solstice."):
@@ -20,6 +20,7 @@ if "solstice.align_island" in sys.modules:
 
 # from .align_island import AlignIsland
 from .export_constraint import ExportConstraint
+from .mirror_mesh import MirrorMeshOperator
 import bpy
 
 
@@ -35,18 +36,29 @@ def bone_menu_func(self, context):
     self.layout.operator(ExportConstraint.bl_idname)
 
 
+def mirror_menu_func(self, context):
+    self.layout.separator()
+    self.layout.label(text="Solstice Toolbox", icon="PLUGIN")
+    self.layout.operator(MirrorMeshOperator.bl_idname)
+
+
 def register():
     # bpy.utils.register_class(AlignIsland)
+    bpy.utils.register_class(MirrorMeshOperator)
     bpy.utils.register_class(ExportConstraint)
     bpy.types.IMAGE_MT_uvs.append(uv_menu_func)
     bpy.types.VIEW3D_MT_object.append(bone_menu_func)
+    bpy.types.VIEW3D_MT_edit_mesh.append(mirror_menu_func)
 
 
 def unregister():
     bpy.types.IMAGE_MT_uvs.remove(uv_menu_func)
     bpy.types.VIEW3D_MT_object.remove(bone_menu_func)
+    bpy.types.VIEW3D_MT_edit_mesh.remove(mirror_menu_func)
+
     # bpy.utils.unregister_class(AlignIsland)
     bpy.utils.unregister_class(ExportConstraint)
+    bpy.utils.unregister_class(MirrorMeshOperator)
 
 
 if __name__ == "__main__":

src/solstice/mirror_mesh.py

@@ -0,0 +1,348 @@
+"""
+Ensures a mesh is mirrored while preserving bone weight data.
+"""
+
+import bpy
+import typing
+import re
+import bmesh
+from dataclasses import dataclass
+from bpy.types import Mesh, Object as BObject
+from bmesh.types import BMesh, BMVert
+from typing import Optional
+from mathutils import Vector
+
+if typing.TYPE_CHECKING:
+    from bpy._typing.rna_enums import OperatorReturnItems
+
+
+BONE_NAME_REGEX = re.compile(
+    r"^(?P<base_name>[a-zA-Z0-9\.\-\_]+?)((?P<side_sep>[\.\-\_])(?P<side>l|r|left|right))?((?P<number_sep>[\.\-\_])(?P<number>\d+))?$",
+    flags=re.IGNORECASE,
+)
+
+
+def is_valid_side(side: str) -> bool:
+    return side.lower() in {"l", "r", "left", "right"}
+
+
+def side_is_left(side: str) -> bool:
+    return side.lower() in {"l", "left"}
+
+
+def flip_side(side: str) -> str:
+    # detect the case of the side
+    if side.isupper():
+        case = "upper"
+    elif side[0].isupper():
+        case = "capital"
+    else:
+        case = "lower"
+
+    def to_case(s: str) -> str:
+        if case == "upper":
+            return s.upper()
+        elif case == "capital":
+            return s.capitalize()
+        else:
+            return s.lower()
+
+    match side.lower():
+        case "l":
+            return to_case("r")
+        case "left":
+            return to_case("right")
+        case "r":
+            return to_case("l")
+        case "right":
+            return to_case("left")
+        case _:
+            raise ValueError(f"Invalid side: {side}")
+
+
+def get_side(vg_name) -> str | None:
+    match = BONE_NAME_REGEX.match(vg_name)
+    if not match:
+        raise ValueError(f"Invalid vertex group name: {repr(vg_name)}")
+    return match.group("side")
+
+
+def recreate_vg_name(vg_name: str, side: str) -> str:
+    match = BONE_NAME_REGEX.match(vg_name)
+    if not match:
+        raise ValueError(f"Invalid vertex group name: {repr(vg_name)}")
+    if match.group("side") is None:
+        raise ValueError(f"Vertex group name does not have a side: {repr(vg_name)}")
+    res = match.group("base_name")
+    if match.group("side_sep") is not None:
+        res += match.group("side_sep")
+    res += side
+    if match.group("number_sep") is not None:
+        res += match.group("number_sep")
+    if match.group("number") is not None:
+        res += match.group("number")
+    return res
+
+
+def vg_side_flipped(vg_name) -> str:
+    match = BONE_NAME_REGEX.match(vg_name)
+    if not match:
+        raise ValueError(f"Invalid vertex group name: {repr(vg_name)}")
+    side = match.group("side")
+    if side is None:
+        raise ValueError(f"Vertex group name does not have a side: {repr(vg_name)}")
+    new_side = flip_side(side)
+    return recreate_vg_name(vg_name, new_side)
+
+
+@dataclass
+class MirrorResult:
+    """
+    Represents the result of a mirror operation.
+    """
+
+    mirror_plane_vtx: set[int]
+    lr_mapping: dict[int, int]
+
+
+class BoneName:
+    """
+    Represents a bone name in `<base_name>(.<l/r>)(.<number>)` format, where:
+    - `.` is the separator, either `.` or `_` or `-`.
+    - `<base_name>` is the base name of the bone.
+    - `<l/r>` is the side of the bone, case insensitive: one of `l`, `r`, `left`, `right`.
+    """
+
+    base_name: str
+    side: Optional[str] = None
+    side_sep: Optional[str] = "."
+    number: Optional[int] = None
+    number_sep: Optional[str] = "."
+
+    def __init__(self, name: str):
+        match = BONE_NAME_REGEX.match(name)
+        if not match:
+            raise ValueError(f"Invalid bone name: {repr(name)}")
+
+        self.base_name = match.group("base_name")
+        self.side = match.group("side")
+        self.side_sep = match.group("side_sep")
+        self.number = int(match.group("number")) if match.group("number") else None
+        self.number_sep = match.group("number_sep")
+
+
+class MirrorMeshOperator(bpy.types.Operator):
+    """Mirror a mesh while preserving bone weight data"""
+
+    bl_idname = "solstice.mirror_mesh"
+    bl_label = "Mirror Mesh"
+    bl_options = {"REGISTER", "UNDO"}
+
+    def execute(self, context) -> set["OperatorReturnItems"]:
+        # Get the active object
+        obj = context.active_object
+        if obj is None or obj.type != "MESH":
+            self.report({"ERROR"}, "No active mesh object found")
+            return {"CANCELLED"}
+
+        # Ensure the object is in edit mode
+        if obj.mode != "EDIT":
+            self.report({"ERROR"}, "Object must be in edit mode")
+            return {"CANCELLED"}
+
+        # Get the mesh data
+        mesh = obj.data
+        if mesh is None or not isinstance(mesh, bpy.types.Mesh):
+            self.report({"ERROR"}, "No mesh data found")
+            return {"CANCELLED"}
+
+        # We don't care about UVs for now; we'll revisit this later
+        # TODO: Add UV mirroring support
+        bm = bmesh.from_edit_mesh(mesh)
+        if bm is None:
+            self.report({"ERROR"}, "No bmesh data found")
+            return {"CANCELLED"}
+
+        res = self._do_mirror(mesh, bm)
+        bm.free()
+
+        # Get out of edit mode
+        bpy.ops.object.mode_set(mode="OBJECT")
+
+        self._mirror_weights(res, obj)
+
+        # Get back into edit mode
+        bpy.ops.object.mode_set(mode="EDIT")
+
+        return {"FINISHED"}
+
+    def _do_mirror(self, mesh: Mesh, bm: BMesh):
+        # We only mirror from left to right, right now.
+
+        mirror_plane_vtx: set[BMVert] = set()
+        left_vtx: set[BMVert] = set()
+        right_vtx: set[BMVert] = set()
+
+        for vtx in bm.verts:
+            x = vtx.co.x
+            if abs(x) < 0.000001:
+                mirror_plane_vtx.add(vtx)
+            elif x < 0:
+                right_vtx.add(vtx)
+            else:
+                left_vtx.add(vtx)
+
+        # Delete all vertices in the right side
+        for vtx in right_vtx:
+            bm.verts.remove(vtx)
+
+        # Create a new vertex for each vertex in the left side
+        left_right_map: dict[BMVert, BMVert] = {}
+        for vtx in left_vtx:
+            new_vtx = bm.verts.new((-vtx.co.x, vtx.co.y, vtx.co.z))
+            new_vtx.normal = Vector((-vtx.normal.x, vtx.normal.y, vtx.normal.z))
+            left_right_map[vtx] = new_vtx
+
+        # Recreate any edges and faces that were connected to the original vertex
+        recreated_edges = set()
+        recreated_faces = set()
+        for vtx in left_vtx:
+            for edge in vtx.link_edges:
+                if edge in recreated_edges:
+                    continue
+                other = edge.other_vert(vtx)
+                try:
+                    if other in left_right_map:
+                        # Create a new edge between the new vertex and the other vertex
+                        bm.edges.new((left_right_map[vtx], left_right_map[other]), edge)
+                    elif other in mirror_plane_vtx:
+                        # Create a new edge between the new vertex and the other vertex
+                        bm.edges.new((left_right_map[vtx], other), edge)
+                    else:
+                        # This edge is not mirrored, so we can just delete it
+                        pass
+                except ValueError:
+                    # This edge already exists, so we can skip it
+                    pass
+
+            for face in vtx.link_faces:
+                if face in recreated_faces:
+                    continue
+                recreated_faces.add(face)
+                new_verts = []
+                for vert in face.verts:
+                    if vert in left_right_map:
+                        new_verts.append(left_right_map[vert])
+                    elif vert in mirror_plane_vtx:
+                        new_verts.append(vert)
+                    else:
+                        # This vertex is not mirrored, so we can just delete it
+                        pass
+                # Create a new face with the new vertices
+                try:
+                    new_face = bm.faces.new(new_verts, face)
+                    new_face.normal_flip()  # because the vertex order is reversed
+                except ValueError:
+                    # This face already exists, so we can skip it
+                    pass
+
+        # Update vertex indexes
+        bm.verts.index_update()
+
+        # Update the mesh
+        bmesh.update_edit_mesh(mesh, loop_triangles=True, destructive=True)
+
+        # Return the mapping of left to right vertices
+        res = MirrorResult(
+            mirror_plane_vtx={vtx.index for vtx in mirror_plane_vtx},
+            lr_mapping={
+                vtx.index: new_vtx.index for vtx, new_vtx in left_right_map.items()
+            },
+        )
+        return res
+
+    def _mirror_weights(self, res: MirrorResult, obj: BObject):
+        vgs = obj.vertex_groups
+        for vg in vgs.values():
+            if vg is None:
+                continue
+
+            def get_weight(vg, weights, vtx: int):
+                try:
+                    w = vg.weight(vtx)
+                    weights[vtx] = w
+                except Exception:
+                    pass
+
+            # Dump weights for later ops
+            weights = {}
+            for vtx in res.lr_mapping.keys():
+                get_weight(vg, weights, vtx)
+            for vtx in res.mirror_plane_vtx:
+                get_weight(vg, weights, vtx)
+
+            side = get_side(vg.name)
+
+            if side is None:
+                # Mirror weights across the mirror plane
+                for vtx, new_vtx in res.lr_mapping.items():
+                    if vtx in weights:
+                        weight = weights[vtx]
+                        vg.add([new_vtx], weight, "REPLACE")
+                    else:
+                        vg.remove([new_vtx])
+                # Vertices on the mirror plane should keep their weights
+
+            elif side_is_left(side):
+                # Handle the left and right sides together
+                right_vg_name = vg_side_flipped(vg.name)
+                right_side = vgs.get(right_vg_name)
+                if right_side is None:
+                    # Create a new vertex group for the right side
+                    right_side = vgs.new(name=right_vg_name)
+
+                # Collect the weights on the left side of the mesh for the flip side
+                right_weights: dict[int, float] = {}
+                for vtx in res.lr_mapping.keys():
+                    get_weight(right_side, right_weights, vtx)
+                for vtx in res.mirror_plane_vtx:
+                    get_weight(right_side, right_weights, vtx)
+
+                # Apply the weights to the left group
+                # Essentially:
+                # - weight originally on the left side is unchanged
+                # - weight collected from (the left side of) the right group is added to the mirrored vertex
+                # - weights on the mirror plane are unchanged (they are not iterated anyway)
+                # - other weights are removed
+                for left, right in res.lr_mapping.items():
+                    if left in weights:
+                        pass  # unchanged
+                    else:
+                        # Remove the weight from the left side
+                        vg.remove([left])
+                    if left in right_weights:
+                        # Add the weight to the right side
+                        right_side.add([right], right_weights[left], "REPLACE")
+                    else:
+                        # Remove the weight from the right side
+                        right_side.remove([right])
+
+                # Apply to the right group
+                # The right group is recreated completely from the left group,
+                # except for the weights on the mirror plane, which are not
+                # iterated anyway
+                for left, right in res.lr_mapping.items():
+                    if left in weights:
+                        # Add the weight to the right side
+                        right_side.add([right], weights[left], "REPLACE")
+                    else:
+                        # Remove the weight from the right side
+                        right_side.remove([right])
+                    if left in right_weights:
+                        right_side.add([left], right_weights[left], "REPLACE")
+                    else:
+                        # Remove the weight from the right side
+                        right_side.remove([left])
+
+            else:
+                pass