ModelTranslator: 减面 ratio/容差纯逻辑（TDD）

Tools/ModelTranslator/bl_decimate.py

@@ -0,0 +1,24 @@
+"""Blender 内运行：FBX 减面到指定三角面数 + Smart UV 重展。
+调用：blender -b --factory-startup --python bl_decimate.py -- <src.fbx> <out.fbx> <target_tris>
+"""
+import os
+import sys
+
+sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
+
+TOLERANCE = 0.03    # 面数相对误差容忍
+MAX_RETRY = 2       # ratio 修正轮数上限
+
+
+def decimate_ratio(target, cur):
+    """Decimate collapse ratio；cur <= target 或非法时返回 1.0（不减面）。"""
+    if cur <= 0 or cur <= target:
+        return 1.0
+    return target / float(cur)
+
+
+def within_tolerance(target, actual, tol=TOLERANCE):
+    """减面结果是否落在目标 ±tol 内。"""
+    if target <= 0:
+        return False
+    return abs(actual - target) <= target * tol

Tools/ModelTranslator/tests/test_bl_decimate.py

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+import os
+import sys
+import unittest
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+import bl_decimate as bd
+
+
+class TestDecimateRatio(unittest.TestCase):
+    def test_normal_reduction(self):
+        self.assertAlmostEqual(bd.decimate_ratio(5000, 1500000), 5000 / 1500000.0)
+
+    def test_current_below_target_returns_one(self):
+        self.assertEqual(bd.decimate_ratio(5000, 3000), 1.0)
+
+    def test_current_equal_target_returns_one(self):
+        self.assertEqual(bd.decimate_ratio(5000, 5000), 1.0)
+
+    def test_zero_current_returns_one(self):
+        self.assertEqual(bd.decimate_ratio(5000, 0), 1.0)
+
+
+class TestWithinTolerance(unittest.TestCase):
+    def test_exact_hit(self):
+        self.assertTrue(bd.within_tolerance(5000, 5000))
+
+    def test_within_3_percent(self):
+        self.assertTrue(bd.within_tolerance(5000, 5150))   # +3%
+        self.assertTrue(bd.within_tolerance(5000, 4850))   # -3%
+
+    def test_outside_3_percent(self):
+        self.assertFalse(bd.within_tolerance(5000, 5200))
+        self.assertFalse(bd.within_tolerance(5000, 4700))
+
+    def test_zero_target_is_false(self):
+        self.assertFalse(bd.within_tolerance(0, 0))
+
+
+if __name__ == "__main__":
+    unittest.main()