ModelTranslator: UV 岛数/翻转/利用率纯逻辑（TDD）

Tools/ModelTranslator/bl_decimate.py

@@ -24,6 +24,38 @@ def within_tolerance(target, actual, tol=TOLERANCE):
     return abs(actual - target) <= target * tol
 
 
+UV_BAD_TOL = 0.02   # 质量门：UV 翻转/重叠面占比超此值则回退 smart_project
+
+
+def count_islands(n_faces, adjacent_pairs):
+    """union-find 数 UV 岛：n_faces 个面，adjacent_pairs 为 UV 连续的面索引对。"""
+    parent = list(range(n_faces))
+
+    def find(i):
+        while parent[i] != i:
+            parent[i] = parent[parent[i]]
+            i = parent[i]
+        return i
+
+    for a, b in adjacent_pairs:
+        ra, rb = find(a), find(b)
+        if ra != rb:
+            parent[ra] = rb
+    return len({find(i) for i in range(n_faces)})
+
+
+def flipped_fraction(signed_areas):
+    """UV 面签名面积为负（翻转）的占比。"""
+    if not signed_areas:
+        return 0.0
+    return sum(1 for a in signed_areas if a < 0) / float(len(signed_areas))
+
+
+def fill_ratio(abs_areas):
+    """UV 空间利用率：面积和（重叠会虚高，截断到 1.0）。"""
+    return min(1.0, sum(abs_areas))
+
+
 # ---------------- 以下仅在 Blender 内执行 ----------------