ModelTranslator: FBX 减面工具 model_decimate（Decimate collapse + Smart UV 重展）

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Tools/ModelTranslator/bl_decimate.py

@@ -22,3 +22,99 @@ def within_tolerance(target, actual, tol=TOLERANCE):
     if target <= 0:
         return False
     return abs(actual - target) <= target * tol
+
+
+# ---------------- 以下仅在 Blender 内执行 ----------------
+
+
+def join_meshes(objs):
+    """多 mesh join 成单对象，返回结果对象（bl_bake 复用）。"""
+    import bpy
+    bpy.ops.object.select_all(action='DESELECT')
+    for o in objs:
+        o.select_set(True)
+    bpy.context.view_layer.objects.active = objs[0]
+    if len(objs) > 1:
+        bpy.ops.object.join()
+    return bpy.context.view_layer.objects.active
+
+
+def _apply_modifier(obj, mod):
+    import bpy
+    bpy.context.view_layer.objects.active = obj
+    bpy.ops.object.modifier_apply(modifier=mod.name)
+
+
+def _triangulate(obj):
+    mod = obj.modifiers.new("mt_tri", 'TRIANGULATE')
+    _apply_modifier(obj, mod)
+
+
+def _decimate(obj, ratio):
+    mod = obj.modifiers.new("mt_dec", 'DECIMATE')
+    mod.decimate_type = 'COLLAPSE'
+    mod.ratio = ratio
+    mod.use_collapse_triangulate = True
+    _apply_modifier(obj, mod)
+
+
+def _smart_unwrap(obj):
+    """删旧 UV 层后 Smart UV Project 重展。island_margin 0.002 ≈ 2048 图 4px。"""
+    import bpy
+    import math
+    mesh = obj.data
+    while mesh.uv_layers:
+        mesh.uv_layers.remove(mesh.uv_layers[0])
+    bpy.context.view_layer.objects.active = obj
+    bpy.ops.object.mode_set(mode='EDIT')
+    bpy.ops.mesh.select_all(action='SELECT')
+    bpy.ops.uv.smart_project(angle_limit=math.radians(66.0), island_margin=0.002)
+    bpy.ops.object.mode_set(mode='OBJECT')
+
+
+def main():
+    import bpy
+    import json
+    argv = sys.argv[sys.argv.index("--") + 1:]
+    src, out_fbx, target = argv[0], argv[1], int(argv[2])
+    warnings = []
+
+    bpy.ops.wm.read_factory_settings(use_empty=True)
+    bpy.ops.import_scene.fbx(filepath=src)
+
+    meshes = [o for o in bpy.data.objects if o.type == 'MESH']
+    skipped = [o.name for o in bpy.data.objects if o.type != 'MESH']
+    if skipped:
+        warnings.append("忽略非 mesh 对象：%s（本工具只处理静态网格）" % ", ".join(skipped))
+    if not meshes:
+        print("MT_SUMMARY " + json.dumps({"error": "FBX 中没有 mesh"}, ensure_ascii=False))
+        return
+    obj = join_meshes(meshes)
+
+    _triangulate(obj)
+    orig = len(obj.data.polygons)
+    cur = orig
+    if cur <= target:
+        warnings.append("当前 %d 面 <= 目标 %d，跳过减面" % (cur, target))
+    else:
+        # collapse 结果是近似值；未达容差时按新面数修正 ratio 再来，最多 MAX_RETRY 轮
+        for _ in range(1 + MAX_RETRY):
+            _decimate(obj, decimate_ratio(target, cur))
+            _triangulate(obj)  # collapse triangulate 后仍可能残留非三角面
+            cur = len(obj.data.polygons)
+            if within_tolerance(target, cur) or cur <= target:
+                break
+
+    _smart_unwrap(obj)
+    out_dir = os.path.dirname(os.path.abspath(out_fbx))
+    os.makedirs(out_dir, exist_ok=True)
+    bpy.ops.export_scene.fbx(filepath=out_fbx, path_mode='STRIP', embed_textures=False)
+
+    print("MT_SUMMARY " + json.dumps(
+        {"src": os.path.basename(src), "fbx": os.path.basename(out_fbx),
+         "tris_before": orig, "tris_after": cur, "target": target,
+         "warnings": warnings}, ensure_ascii=False))
+
+
+if __name__ == "__main__" and "--" in sys.argv:
+    main()

Tools/ModelTranslator/model_decimate.py

@@ -0,0 +1,30 @@
+"""FBX 减面 CLI：减到指定三角面数并 Smart UV 重展，输出 <名>_low.fbx。
+用法：python model_decimate.py src/well1500.fbx --tris 5000 [-o dir] [--blender exe]"""
+import argparse
+import os
+
+from mt_run import find_blender, run_blender_script
+
+
+def main():
+    ap = argparse.ArgumentParser(description=__doc__)
+    ap.add_argument("input", help="FBX 文件")
+    ap.add_argument("--tris", type=int, required=True, help="目标三角面数")
+    ap.add_argument("-o", "--out", default=None, help="输出目录（默认源文件同目录）")
+    ap.add_argument("--blender", default=None)
+    args = ap.parse_args()
+
+    blender = find_blender(args.blender)
+    name = os.path.splitext(os.path.basename(args.input))[0]
+    outdir = args.out or os.path.dirname(os.path.abspath(args.input))
+    out_fbx = os.path.join(outdir, name + "_low.fbx")
+    s = run_blender_script(blender, "bl_decimate.py",
+                           [args.input, out_fbx, str(args.tris)])
+    print("== %s: %d -> %d 面（目标 %d）-> %s" %
+          (s["src"], s["tris_before"], s["tris_after"], s["target"], out_fbx))
+    for w in s["warnings"]:
+        print("  [警告] %s" % w)
+
+
+if __name__ == "__main__":
+    main()