ModelTranslator: 展开路径接入 UVPM4 排布——保底+增强，失败回退内置 pack

Tools/ModelTranslator/bl_decimate.py

@@ -103,6 +103,9 @@ def _decimate(obj, ratio):
 
 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
+UVPM_PIXEL_MARGIN = 4   # UVPM 岛间距（像素），与 PACK_MARGIN * UVPM_TEX_SIZE 同口径
+UVPM_TEX_SIZE = 2048
 
 
 def _clear_uv_layers(mesh):
@@ -204,21 +207,81 @@ def _overlap_fraction(obj):
     return round(sum(1 for p in polys if p.select) / float(len(polys)), 4)
 
 
+_uvpm_failed = False    # 进程内失败一次即不再重试（避免重复警告与启动开销）
+
+
+def _uvpm_enable():
+    """启用 UVPM4 扩展（幂等）。headless 下先补丁 GPU shader 创建——
+    UVPM4 导入期为视口覆盖层建 shader，后台模式无 GPU 绘图会 SystemError；
+    覆盖层仅交互用，pack 不受影响。引擎路径经注册表自动发现。"""
+    import bpy
+    import addon_utils
+    if bpy.app.background:
+        import gpu
+        orig = gpu.shader.from_builtin
+        if not getattr(orig, "_mt_safe", False):
+            def _safe(*a, **k):
+                try:
+                    return orig(*a, **k)
+                except SystemError:
+                    return None
+            _safe._mt_safe = True
+            gpu.shader.from_builtin = _safe
+    # default_set=True 才建 preferences.addons 条目（UVPM4 register 依赖）；
+    # factory-startup 关闭偏好自动保存，不会写盘
+    if addon_utils.enable(UVPM_EXT, default_set=True) is None:
+        raise RuntimeError("扩展 %s 启用失败（未安装或版本不兼容）" % UVPM_EXT)
+
+
+def _uvpm_repack(obj, warnings):
+    """UVPM4 重排当前 UV 布局，成功返回 True；任何失败记警告返回 False，
+    保底布局（pack_islands/smart_project）原样保留。"""
+    global _uvpm_failed
+    if _uvpm_failed:
+        return False
+    import bpy
+    try:
+        _uvpm_enable()
+        p = bpy.context.scene.uvpm4_props.default_main_props
+        p.pixel_margin_enable = True
+        p.pixel_margin = UVPM_PIXEL_MARGIN
+        p.pixel_margin_tex_size = UVPM_TEX_SIZE
+        bpy.context.scene.tool_settings.use_uv_select_sync = True
+        bpy.context.view_layer.objects.active = obj
+        bpy.ops.object.mode_set(mode='EDIT')
+        bpy.ops.mesh.select_all(action='SELECT')
+        try:
+            ret = bpy.ops.uvpackmaster4.pack(mode_id='pack.single_tile',
+                                             pack_op_type='0')
+        finally:
+            bpy.ops.object.mode_set(mode='OBJECT')
+        if 'FINISHED' not in ret:
+            raise RuntimeError("pack 返回 %s" % sorted(ret))
+        return True
+    except Exception as e:
+        _uvpm_failed = True
+        warnings.append("UVPackmaster 排布不可用（%s），沿用内置 pack 布局" % e)
+        return False
+
+
 def _do_unwrap(obj, mode, warnings):
-    """按模式展开；seam 质量不达标自动回退 smart。返回 uv 指标 dict（含 mode）。"""
+    """按模式展开（排布默认 UVPM4 增强，失败保底内置 pack）；
+    seam 质量不达标自动回退 smart。返回 uv 指标 dict（含 mode）。"""
     if mode == "seam":
         _unwrap_seam(obj, warnings)
+        uvpm = _uvpm_repack(obj, warnings)
         m = _collect_uv_metrics(obj)
         if uv_gate_ok(m["flipped"], m["overlap"]):
-            m["mode"] = "seam"
+            m["mode"] = uvpm_mode_label("seam", uvpm)
             return m
         warnings.append("seam 展开质量不达标（翻转 %.1f%% 重叠 %s），回退 smart_project"
                         % (m["flipped"] * 100,
                            "%.1f%%" % (m["overlap"] * 100) if m["overlap"] is not None else "未知"))
         mode = "smart_fallback"
     _unwrap_smart(obj)
+    uvpm = _uvpm_repack(obj, warnings)
     m = _collect_uv_metrics(obj)
-    m["mode"] = mode if mode == "smart_fallback" else "smart"
+    m["mode"] = uvpm_mode_label(mode if mode == "smart_fallback" else "smart", uvpm)
     return m