"""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