ModelTranslator: 减面前 _clean_mesh 焊接重合点+去退化面

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Tools/ModelTranslator/bl_decimate.py

@@ -112,6 +112,30 @@ def _decimate(obj, ratio):
     _apply_modifier(obj, mod)
 
 
+def _clean_mesh(obj, warnings):
+    """减面前清理：按局部包围盒对角线相对焊接重合点 + 去退化面，给 collapse 更干净的流形，
+    减少被迫加的 seam。各步失败降级不中断。"""
+    import bpy
+    import mathutils
+    bb = [mathutils.Vector(c) for c in obj.bound_box]
+    diag = (bb[0] - bb[6]).length
+    bpy.context.view_layer.objects.active = obj
+    bpy.ops.object.mode_set(mode='EDIT')
+    bpy.ops.mesh.select_all(action='SELECT')
+    if diag > 0.0:
+        try:
+            bpy.ops.mesh.remove_doubles(threshold=diag * REL_WELD)
+        except RuntimeError as e:
+            warnings.append("remove_doubles 失败（%s），跳过焊接" % e)
+    else:
+        warnings.append("包围盒对角线为 0，跳过焊接")
+    try:
+        bpy.ops.mesh.dissolve_degenerate()
+    except RuntimeError as e:
+        warnings.append("dissolve_degenerate 失败（%s），跳过去退化" % e)
+    bpy.ops.object.mode_set(mode='OBJECT')
+
+
 SEAM_ANGLE_DEG = 66.0   # 锐边阈值：两面夹角超此值标 seam
 PACK_MARGIN = 0.002     # 岛间距 ≈ 2048 图 4px
 UVPM_EXT = "bl_ext.user_default.uvpackmaster4"   # UVPackmaster 4 扩展模块名
@@ -119,6 +143,7 @@ UVPM_PIXEL_MARGIN = 4   # UVPM 岛间距（像素），与 PACK_MARGIN * UVPM_TE
 UVPM_TEX_SIZE = 2048
 SEAM_ANGLE_SWEEP = (55.0, 45.0, 35.0)   # 首选 SEAM_ANGLE_DEG 不过门时依次下探的 seam 角度
 STRETCH_ITERS = 30                       # minimize_stretch 松弛迭代次数
+REL_WELD = 1e-4   # 焊接距离占局部包围盒对角线比例（避免 cm/m 单位差异导致绝对阈值失准）
 
 
 def _clear_uv_layers(mesh):
@@ -364,6 +389,7 @@ def main():
         return
     obj = join_meshes(meshes)
 
+    _clean_mesh(obj, warnings)
     _triangulate(obj)
     orig = len(obj.data.polygons)
     cur = orig