序：为什么小游戏值得单独写一套书

# file: sim/ch00_constraint_budget.py
# tier: S
# verify: /opt/homebrew/bin/python3 sim/ch00_constraint_budget.py --config config/ --out out/
"""平台约束预算：把「首包多大、冷启动多快、单局多长」翻译成可分配的资源名额。

读 config/ch00_budget.json（全整数，单位 KB / 秒 / 毫秒），算出：
  - 首包扣掉代码体积后，还能放多少张贴图、多少段音频；
  - 分包里能放多少关配置；
  - 冷启动预算内最多加载多少资源；
  - 单局目标时长下，玩家要经历多少次核心循环、多少次正反馈。
产出 JSON + CSV + SVG，正文引用的都是这里的真实输出（同机相对量级）。
"""

from __future__ import annotations

import argparse
import json
import os
import xml.etree.ElementTree as ET

import pandas as pd


def load(path: str) -> dict:
    with open(path, encoding="utf-8") as f:
        return json.load(f)


def compute(cfg: dict) -> dict:
    pkg, load, sess = cfg["package"], cfg["load"], cfg["session"]
    code = pkg["codeBudgetKB"]

    first_left = pkg["firstPackageBudgetKB"] - code
    atlas_in_first = first_left // pkg["atlasAssetKB"]
    audio_in_first = first_left // pkg["audioAssetKB"]
    # 首包只放「立刻要看到」的资源，贴图按一半名额预留给后续按需加载
    atlas_immediate = atlas_in_first // 2

    sub_left = pkg["subpackageBudgetKB"] - code
    levels_in_sub = sub_left // pkg["levelConfigKB"]

    cold_start_assets = load["coldStartBudgetMs"] // load["perAssetLoadMs"]
    loops_per_session = sess["sessionTargetSec"] // sess["coreLoopSec"]
    feedback_per_session = sess["sessionTargetSec"] // sess["feedbackEverySec"]

    return {
        "firstLeftKB": first_left,
        "atlasInFirst": atlas_in_first,
        "audioInFirst": audio_in_first,
        "atlasImmediate": atlas_immediate,
        "levelsInSub": levels_in_sub,
        "coldStartAssets": cold_start_assets,
        "loopsPerSession": loops_per_session,
        "feedbackPerSession": feedback_per_session,
    }


def write_svg(path: str, labels: list[str], values: list[int], title: str) -> int:
    W, H, PAD = 640, 360, 48
    v_max = max(values) or 1
    bar_w = (W - 2 * PAD) / len(values) * 0.6
    gap = (W - 2 * PAD) / len(values)
    p = [
        f'<svg xmlns="http://www.w3.org/2000/svg" width="{W}" height="{H}" viewBox="0 0 {W} {H}">',
        f'<rect width="{W}" height="{H}" fill="#ffffff"/>',
        f'<text x="{PAD}" y="{PAD - 20}" font-size="14" fill="#111827">{title}</text>',
    ]
    for i, (lab, val) in enumerate(zip(labels, values)):
        x = PAD + gap * i + (gap - bar_w) / 2
        h = (H - 2 * PAD) * (val / v_max)
        y = H - PAD - h
        p.append(f'<rect x="{x:.1f}" y="{y:.1f}" width="{bar_w:.1f}" height="{h:.1f}" fill="#2563eb"/>')
        p.append(f'<text x="{x + bar_w / 2:.1f}" y="{y - 6:.1f}" font-size="11" text-anchor="middle" fill="#111827">{val}</text>')
        p.append(f'<text x="{x + bar_w / 2:.1f}" y="{H - PAD + 16:.1f}" font-size="10" text-anchor="middle" fill="#6b7280">{lab}</text>')
    p.append(f'<line x1="{PAD}" y1="{H - PAD}" x2="{W - PAD}" y2="{H - PAD}" stroke="#9ca3af"/>')
    p.append("</svg>")
    svg = "\n".join(p)
    with open(path, "w", encoding="utf-8") as f:
        f.write(svg)
    ET.fromstring(svg)
    return len(svg.encode())


def main() -> int:
    ap = argparse.ArgumentParser()
    ap.add_argument("--config", default="config/")
    ap.add_argument("--out", default="out/")
    args = ap.parse_args()

    os.makedirs(args.out, exist_ok=True)
    cfg = load(os.path.join(args.config, "ch00_budget.json"))
    r = compute(cfg)

    rows = [
        ("首包可放贴图", r["atlasInFirst"]),
        ("首包可放音频", r["audioInFirst"]),
        ("分包可放关卡", r["levelsInSub"]),
        ("冷启动可加载资源", r["coldStartAssets"]),
        ("单局核心循环", r["loopsPerSession"]),
        ("单局正反馈", r["feedbackPerSession"]),
    ]
    df = pd.DataFrame(rows, columns=["item", "count"])
    df.to_csv(os.path.join(args.out, "ch00_budget.csv"), index=False)

    svg_bytes = write_svg(
        os.path.join(args.out, "ch00_budget.svg"),
        [x[0] for x in rows],
        [x[1] for x in rows],
        "《合成小岛》平台约束下的资源名额",
    )

    report = {
        "source": "sim/ch00_constraint_budget.py",
        "config": os.path.join(args.config, "ch00_budget.json"),
        **r,
        "csv": os.path.join(args.out, "ch00_budget.csv"),
        "svg": os.path.join(args.out, "ch00_budget.svg"),
        "svgBytes": svg_bytes,
    }
    with open(os.path.join(args.out, "ch00_budget.json"), "w", encoding="utf-8") as f:
        json.dump(report, f, ensure_ascii=False, indent=2)
    print(json.dumps(report, ensure_ascii=False))
    return 0


if __name__ == "__main__":
    raise SystemExit(main())

{"source": "sim/ch00_constraint_budget.py", "config": "config/ch00_budget.json", "firstLeftKB": 3584, "atlasInFirst": 37, "audioInFirst": 74, "atlasImmediate": 18, "levelsInSub": 3328, "coldStartAssets": 250, "loopsPerSession": 6, "feedbackPerSession": 12, "csv": "out/ch00_budget.csv", "svg": "out/ch00_budget.svg", "svgBytes": 1865}