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perf(cff): Local Subr INDEX 子集化，思源 OTF woff2 641KB→10KB(-98%)
思源 OTF 的 FD12 Local Subr INDEX 含 26550 个子程序(716KB)被完整透传， 但子集 18 字形仅引用 13 个。新增 Type 2 栈模拟扫描 collectSubrRefs (精确跟踪 stem 计数以正确跳过 hintmask/cntrmask 掩码字节)递归收集引用， 按 Private 池构建 localRemap + writeIndex 重建紧凑 INDEX， rewriteCharstring 重写 callsubr 操作数到新编号。 收益(otf-思源黑体子集)： - woff2 641480→10664 bytes (-98.3%) - ttf 752040→19188 bytes (-97.4%) - min 5.69ms→1.50ms (brotli 输入缩小，-73.6%) - SSIM 保持 1.0000 global subr 不子集化(思源引用=0，仅 6KB)；privSegCache 去重保留。 Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚）
parent
f1c8315b0c
commit
70d3a2a3dc
@ -138,6 +138,219 @@ function encodeDictInt(v: number): number[] {
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return [29, (v >>> 24) & 0xff, (v >> 16) & 0xff, (v >> 8) & 0xff, v & 0xff];
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}
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/** Type 2 charstring 操作码（Adobe Type 2 Charstring Format）。 */
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const T2_CALLSUBR = 10;
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const T2_RETURN = 11;
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const T2_ENDCHAR = 14;
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const T2_HSTEM = 1;
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const T2_VSTEM = 3;
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const T2_HSTEMHM = 18;
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const T2_VSTEMHM = 23;
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const T2_HINTMASK = 19;
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const T2_CNTRMASK = 20;
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const T2_CALLGSUBR = 29;
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/** 计算 subr INDEX 的 bias（CFF 规范：调用编号 = 实际 subr 索引 + bias）。
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* nSubrs < 1240 → 107；< 33900 → 1131；否则 32768。 */
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function subrBias(nSubrs: number): number {
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if (nSubrs < 1240) return 107;
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if (nSubrs < 33900) return 1131;
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return 32768;
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}
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/**
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* 扫描单个 Type 2 charstring/subr 字节，收集其引用的 local subr 与 global subr 编号。
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* 采用栈模拟：operand 依次入栈，遇 callsubr(10)/callgsubr(29) 取栈顶为调用编号（减 bias 得实际索引）。
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*
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* hintmask(19)/cntrmask(20) 后跟 ceil(stemCount/8) 字节掩码，必须跳过——否则掩码字节会被
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* 误判为操作码致扫描错位、漏收引用（思源 charstring 大量使用 hint）。
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* stemCount 由 stem 类操作码（hstem/vstem/hstemhm/vstemhm）的栈深度累加（每 stem = 2 operand）。
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*
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* @param b CFF 字节
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* @param start charstring/subr 起始偏移
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* @param end charstring/subr 结束偏移（不含）
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* @param localBias 该 charstring 所属 FD 的 local subr bias
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* @param localCount local subr 总数（越界保护）
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* @param localRefs 输出：收集到的 local subr 实际索引
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* @param gsubrRefs 输出：收集到的 global subr 实际索引
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*/
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export function collectSubrRefs(
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b: Uint8Array,
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start: number,
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end: number,
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localBias: number,
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localCount: number,
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localRefs: Set<number>,
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gsubrRefs: Set<number>,
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): void {
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let p = start;
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const stack: number[] = [];
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let stemCount = 0;
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while (p < end) {
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const b0 = b[p++];
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if (b0 === 255) {
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/** fixed point（坐标），4 字节，不入栈编号判定 */
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stack.push(NaN);
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p += 4;
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} else if (b0 === 28) {
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stack.push(((b[p] << 24) | (b[p + 1] << 16)) >> 16);
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p += 2;
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} else if (b0 === 29) {
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stack.push(((b[p] << 24) | (b[p + 1] << 16) | (b[p + 2] << 8) | b[p + 3]) | 0);
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p += 4;
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} else if (b0 >= 32 && b0 <= 246) {
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stack.push(b0 - 139);
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} else if (b0 >= 247 && b0 <= 250) {
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stack.push((b0 - 247) * 256 + b[p] + 108);
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p += 1;
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} else if (b0 >= 251 && b0 <= 254) {
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stack.push(-(b0 - 251) * 256 - b[p] - 108);
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p += 1;
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} else {
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/** 操作码（b0 <= 27，含 12 双字节） */
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if (b0 === 12) {
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p += 1;
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stack.length = 0;
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} else if (b0 === T2_HSTEM || b0 === T2_VSTEM || b0 === T2_HSTEMHM || b0 === T2_VSTEMHM) {
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stemCount += stack.length >> 1;
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stack.length = 0;
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} else if (b0 === T2_HINTMASK || b0 === T2_CNTRMASK) {
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p += (stemCount + 7) >>> 3;
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stack.length = 0;
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} else if (b0 === T2_CALLSUBR) {
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const arg = stack[stack.length - 1];
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if (Number.isInteger(arg)) {
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const sn = arg + localBias;
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if (sn >= 0 && sn < localCount) localRefs.add(sn);
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}
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stack.length = 0;
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} else if (b0 === T2_CALLGSUBR) {
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const arg = stack[stack.length - 1];
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if (Number.isInteger(arg)) gsubrRefs.add(arg);
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stack.length = 0;
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} else if (b0 === T2_ENDCHAR) {
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break;
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} else {
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/** 其余操作码（运动/曲线等）消费栈 */
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stack.length = 0;
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}
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}
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}
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}
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/**
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* 重写 Type 2 charstring/subr：把 callsubr/callgsubr 的调用编号 operand 重映射到子集编号。
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* 其余字节原样保留（坐标、操作码、hintmask 掩码等）。
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*
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* 实现：逐字节复制到输出，operand 入栈时记录其在输出的起始位置；遇 callsubr/callgsubr 时
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* 截断输出回栈顶 operand 起始处，写入新编号编码（operand 编码长度可能变化，故必须重建流而非原地改）。
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*
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* @param b CFF 字节
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* @param start charstring 起始偏移
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* @param end charstring 结束偏移
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* @param localBias 原 local subr bias（解析 operand 用）
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* @param localRemap 旧 local subr 索引 → 新索引（-1 表示未保留，不该出现于引用 charstring）
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* @param newLocalCount 新 local subr 总数（算新 bias）
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* @returns 重写后的字节。global subr 不子集化（callgsubr operand 原样保留，bias 不变）。
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*/
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export function rewriteCharstring(
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b: Uint8Array,
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start: number,
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end: number,
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localBias: number,
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localRemap: Map<number, number>,
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newLocalCount: number,
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): Uint8Array {
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const newLocalBias = subrBias(newLocalCount);
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const out: number[] = [];
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/** 栈：记录每个 operand 在 out 中的起始位置（便于截断重写）。值为原始解析值。 */
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const stackStart: number[] = [];
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const stackVal: number[] = [];
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let stemCount = 0;
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let p = start;
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while (p < end) {
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const b0 = b[p++];
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if (b0 === 255) {
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stackStart.push(out.length);
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stackVal.push(NaN);
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out.push(255, b[p], b[p + 1], b[p + 2], b[p + 3]);
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p += 4;
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} else if (b0 === 28) {
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stackStart.push(out.length);
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stackVal.push(((b[p] << 24) | (b[p + 1] << 16)) >> 16);
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out.push(28, b[p], b[p + 1]);
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p += 2;
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} else if (b0 === 29) {
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stackStart.push(out.length);
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stackVal.push(((b[p] << 24) | (b[p + 1] << 16) | (b[p + 2] << 8) | b[p + 3]) | 0);
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out.push(29, b[p], b[p + 1], b[p + 2], b[p + 3]);
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p += 4;
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} else if (b0 >= 32 && b0 <= 246) {
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stackStart.push(out.length);
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stackVal.push(b0 - 139);
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out.push(b0);
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} else if (b0 >= 247 && b0 <= 250) {
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stackStart.push(out.length);
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stackVal.push((b0 - 247) * 256 + b[p] + 108);
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out.push(b0, b[p]);
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p += 1;
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} else if (b0 >= 251 && b0 <= 254) {
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stackStart.push(out.length);
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stackVal.push(-(b0 - 251) * 256 - b[p] - 108);
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out.push(b0, b[p]);
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p += 1;
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} else {
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/** 操作码 */
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if (b0 === 12) {
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out.push(12, b[p]);
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p += 1;
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stackStart.length = 0;
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stackVal.length = 0;
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} else if (b0 === T2_HSTEM || b0 === T2_VSTEM || b0 === T2_HSTEMHM || b0 === T2_VSTEMHM) {
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stemCount += stackVal.length >> 1;
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out.push(b0);
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stackStart.length = 0;
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stackVal.length = 0;
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} else if (b0 === T2_HINTMASK || b0 === T2_CNTRMASK) {
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out.push(b0);
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const maskBytes = (stemCount + 7) >>> 3;
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for (let i = 0; i < maskBytes; i++) out.push(b[p + i]);
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p += maskBytes;
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stackStart.length = 0;
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stackVal.length = 0;
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} else if (b0 === T2_CALLSUBR) {
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const arg = stackVal[stackVal.length - 1];
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const oldSn = Number.isInteger(arg) ? arg + localBias : -1;
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const newSn = localRemap.get(oldSn);
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if (newSn === undefined) {
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/** subr 未保留（理论上引用 charstring 必命中）——保留原 operand 保底 */
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out.push(T2_CALLSUBR);
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} else {
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/** 截断到栈顶 operand 起始，写入新编号编码 */
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out.length = stackStart[stackStart.length - 1];
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for (const eb of encodeDictInt(newSn - newLocalBias)) out.push(eb);
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out.push(T2_CALLSUBR);
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}
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stackStart.length = 0;
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stackVal.length = 0;
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} else if (b0 === T2_CALLGSUBR) {
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/** global subr 不子集化：operand（调用编号）原样保留，bias 不变 */
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out.push(T2_CALLGSUBR);
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stackStart.length = 0;
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stackVal.length = 0;
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} else if (b0 === T2_ENDCHAR) {
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out.push(b0);
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break;
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} else {
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out.push(b0);
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stackStart.length = 0;
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stackVal.length = 0;
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}
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}
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}
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return new Uint8Array(out);
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}
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/**
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* 序列化 CFF INDEX：count + offSize + (count+1)*offSize 偏移量 + 数据拼接。
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* 选最小能容纳最大偏移量的 offSize。偏移量 1-based（首个 offset=1）。
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@ -344,10 +557,11 @@ export function subsetCFF(cffBytes: Uint8Array, subsetGids: number[]): Uint8Arra
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/** .notdef（gid 0）必须保留，且 subsetGids[0] 应为 0 */
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const newSubsetGids = subsetGids[0] === 0 ? subsetGids : [0, ...subsetGids];
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/** 重建 CharStrings INDEX：按 newSubsetGids 顺序透传原 charstring 字节。
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* 按 gid 随机读 2 个 offset 取区间，跳过全量 offset 遍历。 */
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const newCharStringObjects: { bytes: Uint8Array; start: number; len: number }[] = [];
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for (const gid of newSubsetGids) {
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/** 先记录每个子集字形在原 CharStrings 的字节区间 [start, end)，供后续 subr 子集化重写。 */
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const newSubsetNumGlyphs = newSubsetGids.length;
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const charStringRanges: { start: number; end: number }[] = new Array(newSubsetNumGlyphs);
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for (let gi = 0; gi < newSubsetNumGlyphs; gi++) {
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const gid = newSubsetGids[gi];
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/** 读 offset[gid] 与 offset[gid+1]（offSize 字节大端） */
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let o0 = 0;
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let o1 = 0;
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@ -355,17 +569,13 @@ export function subsetCFF(cffBytes: Uint8Array, subsetGids: number[]): Uint8Arra
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const p1 = csOffArrStart + (gid + 1) * csOffSize;
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for (let j = 0; j < csOffSize; j++) o0 = (o0 << 8) | b[p0 + j];
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for (let j = 0; j < csOffSize; j++) o1 = (o1 << 8) | b[p1 + j];
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const s = csDataStart + o0 - 1;
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const e = csDataStart + o1 - 1;
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newCharStringObjects.push({ bytes: b, start: s, len: e - s });
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charStringRanges[gi] = { start: csDataStart + o0 - 1, end: csDataStart + o1 - 1 };
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}
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const newCharStrings = writeIndex(newCharStringObjects);
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/** 重建 charset：CID-keyed 字体的 charset 是 gid→CID 映射。格式 0/1/2，按 newSubsetGids 取 CID。
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* CID 0 固定留给 .notdef（gid 0），其余按原 charset 顺序。新 charset 用格式 0 最简单：
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* format(1) + (numGlyphs-1)×CID(u16)（charset 不含 gid 0，它隐式为 CID 0）。
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* 按需查 CID（lookupCharsetCID 遍历 range 查单个 gid），不全量展开 65535 项。 */
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const newSubsetNumGlyphs = newSubsetGids.length;
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const newCharsetBody: number[] = [];
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for (let i = 1; i < newSubsetNumGlyphs; i++) {
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/** newSubsetGids[i] 是原始 gid，取其原 CID */
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@ -403,10 +613,24 @@ export function subsetCFF(cffBytes: Uint8Array, subsetGids: number[]): Uint8Arra
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len: number;
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/** Local Subr INDEX 原始字节（无则 null）。思源等 CID 字体字形通过 callsubr 引用本地 subr */
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localSubr: Uint8Array | null;
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/** Local Subr INDEX 全量解析（off→字节区间），供引用收集与重建；null 表示无 local subr */
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localSubrIdx: CffIndex | null;
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/** 原 local subr bias（localSubrIdx.count 决定） */
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localBias: number;
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/** 子集 local subr 旧索引→新索引映射（引用收集后填充）；null 表示无需重映射（无 subr 或全保留） */
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localRemap: Map<number, number> | null;
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/** 子集后 local subr 总数 */
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newLocalCount: number;
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/** 子集 local subr INDEX 字节（重建后；无 subr 为 null）。最终拼入 Private 段 */
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newLocalSubr: Uint8Array | null;
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}
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interface FdInfo { dictBytes: Uint8Array; priv: PrivInfo; }
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/** 原始 Private 段去重：相同 origOff 的 Private 共享同一份（含其 Local Subr） */
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const privSegCache = new Map<number, PrivInfo>();
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/** 每个 unique Private 池（按 privOrigOff）收集的 local subr 引用集（多 FD 共享一池时合并） */
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const privLocalRefs = new Map<number, Set<number>>();
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/** global subr 不子集化，collectSubrRefs 的 gsubrRefs 参数占位（引用不收集） */
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const dummyGsubrRefs = new Set<number>();
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const fdInfos: FdInfo[] = [];
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for (const fd of usedFds) {
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const s = fdArrayIndex.dataStart + fdArrayIndex.offsets[fd] - 1;
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@ -416,7 +640,7 @@ export function subsetCFF(cffBytes: Uint8Array, subsetGids: number[]): Uint8Arra
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const priv = fdDict.get(OP_Private);
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/** 无 Private 的 FD（极罕见）原样透传 */
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if (!priv || priv.length < 2) {
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fdInfos.push({ dictBytes, priv: { origOff: -1, len: 0, localSubr: null } });
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fdInfos.push({ dictBytes, priv: { origOff: -1, len: 0, localSubr: null, localSubrIdx: null, localBias: 0, localRemap: null, newLocalCount: 0, newLocalSubr: null } });
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continue;
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}
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const privLen = priv[0];
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@ -427,18 +651,105 @@ export function subsetCFF(cffBytes: Uint8Array, subsetGids: number[]): Uint8Arra
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const privDict = parseDict(b, privOrigOff, privOrigOff + privLen);
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const subrRel = privDict.get(OP_LocalSubr)?.[0];
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let localSubr: Uint8Array | null = null;
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let localSubrIdx: CffIndex | null = null;
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let localBias = 0;
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if (subrRel !== undefined) {
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/** Local Subr INDEX 紧接 Private DICT 字节之后（绝对偏移 = privOrigOff + subrRel） */
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/** Local Subr INDEX 仅需整体字节切片透传，不全量解析 offset（思源 Local Subr 可达数千 subr） */
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const subrRange = indexByteRange(b, privOrigOff + subrRel);
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localSubr = b.subarray(subrRange.start, subrRange.end);
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const subrAbs = privOrigOff + subrRel;
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/** 全量解析 INDEX（含所有 offset）：引用收集需按 subr 编号读字节区间，
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* 子集重建需重排 offset。仅命中的 Private 才解析（思源仅 1-2 个 FD 有 subr）。 */
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localSubrIdx = readIndex(b, subrAbs);
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localBias = subrBias(localSubrIdx.count);
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localSubr = b.subarray(localSubrIdx.start, localSubrIdx.end);
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}
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info = { origOff: privOrigOff, len: privLen, localSubr };
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info = { origOff: privOrigOff, len: privLen, localSubr, localSubrIdx, localBias, localRemap: null, newLocalCount: localSubrIdx ? localSubrIdx.count : 0, newLocalSubr: localSubr };
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privSegCache.set(privOrigOff, info);
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privLocalRefs.set(privOrigOff, new Set());
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}
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fdInfos.push({ dictBytes, priv: info });
|
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/** 收集该 FD 所有子集字形的 local subr 引用到其 Private 池的引用集 */
|
||||
const refs = privLocalRefs.get(info.origOff)!;
|
||||
if (info.localSubrIdx) {
|
||||
const idx = info.localSubrIdx;
|
||||
for (let i = 0; i < newSubsetNumGlyphs; i++) {
|
||||
if (gidOrigFds[i] !== fd) continue;
|
||||
const r = charStringRanges[i];
|
||||
collectSubrRefs(b, r.start, r.end, info.localBias, idx.count, refs, dummyGsubrRefs);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/** 递归收敛：被引用的 local subr 可能再引用其他 local subr，迭代至不动点。
|
||||
* （global subr 不子集化，故不收集 gsubr 引用；collectSubrRefs 的 gsubrRefs 占位用 dummyGsubrRefs） */
|
||||
if (privLocalRefs.size > 0) {
|
||||
let changed = true;
|
||||
let guard = 0;
|
||||
while (changed && guard < 64) {
|
||||
changed = false;
|
||||
guard++;
|
||||
for (const [privOrigOff, refs] of privLocalRefs) {
|
||||
const info = privSegCache.get(privOrigOff)!;
|
||||
const idx = info.localSubrIdx;
|
||||
if (!idx) continue;
|
||||
const before = refs.size;
|
||||
for (const sn of [...refs]) {
|
||||
const ss = idx.dataStart + idx.offsets[sn] - 1;
|
||||
const se = idx.dataStart + idx.offsets[sn + 1] - 1;
|
||||
collectSubrRefs(b, ss, se, info.localBias, idx.count, refs, dummyGsubrRefs);
|
||||
}
|
||||
if (refs.size > before) changed = true;
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
/** 各 Private 池：构建旧→新 local subr 映射 + 重建子集 INDEX。引用为空则保留空 INDEX。 */
|
||||
for (const [privOrigOff, refs] of privLocalRefs) {
|
||||
const info = privSegCache.get(privOrigOff)!;
|
||||
const idx = info.localSubrIdx;
|
||||
if (!idx) continue;
|
||||
const sortedRefs = [...refs].sort((a, c) => a - c);
|
||||
const remap = new Map<number, number>();
|
||||
for (let i = 0; i < sortedRefs.length; i++) remap.set(sortedRefs[i], i);
|
||||
info.localRemap = remap;
|
||||
info.newLocalCount = sortedRefs.length;
|
||||
if (sortedRefs.length === 0) {
|
||||
/** 无引用：输出空 INDEX（count=0，2 字节），newLocalSubr 占位（下方 patchPrivateDict 后拼入） */
|
||||
info.newLocalSubr = new Uint8Array(2);
|
||||
} else {
|
||||
/** 重建 INDEX：按新顺序写出被引用的 subr 字节。subr 内部 callsubr 也需重映射（递归 patch） */
|
||||
const objects: { bytes: Uint8Array; start: number; len: number }[] = [];
|
||||
for (const oldSn of sortedRefs) {
|
||||
const ss = idx.dataStart + idx.offsets[oldSn] - 1;
|
||||
const se = idx.dataStart + idx.offsets[oldSn + 1] - 1;
|
||||
const rewritten = rewriteCharstring(b, ss, se, info.localBias, remap, sortedRefs.length);
|
||||
objects.push({ bytes: rewritten, start: 0, len: rewritten.length });
|
||||
}
|
||||
info.newLocalSubr = writeIndex(objects);
|
||||
}
|
||||
}
|
||||
|
||||
/** 重建 CharStrings INDEX：按 newSubsetGids 顺序输出 charstring。
|
||||
* 所属 FD 有 local subr 子集化时，patch callsubr operand（重映射到新 subr 编号 - 新 bias）；
|
||||
* 否则透传原 charstring 字节。global subr 不子集化，callgsubr operand 原样保留。 */
|
||||
const newCharStringObjects: { bytes: Uint8Array; start: number; len: number }[] = [];
|
||||
for (let gi = 0; gi < newSubsetNumGlyphs; gi++) {
|
||||
const r = charStringRanges[gi];
|
||||
const origFd = gidOrigFds[gi];
|
||||
/** 该 gid 所属原 FD 对应的 Private 信息（经 privSegCache 去重，按 privOrigOff 查） */
|
||||
let privInfo: PrivInfo | null = null;
|
||||
/** usedFds 顺序与 fdInfos 一致，反查 origFd→privInfo */
|
||||
for (let fi = 0; fi < usedFds.length; fi++) {
|
||||
if (usedFds[fi] === origFd) { privInfo = fdInfos[fi].priv; break; }
|
||||
}
|
||||
if (privInfo && privInfo.localRemap) {
|
||||
const rewritten = rewriteCharstring(b, r.start, r.end, privInfo.localBias, privInfo.localRemap, privInfo.newLocalCount);
|
||||
newCharStringObjects.push({ bytes: rewritten, start: 0, len: rewritten.length });
|
||||
} else {
|
||||
newCharStringObjects.push({ bytes: b, start: r.start, len: r.end - r.start });
|
||||
}
|
||||
}
|
||||
const newCharStrings = writeIndex(newCharStringObjects);
|
||||
|
||||
/** 新 FDSelect：每个新 gid → 新 FD 编号（复用首次遍历的 gidOrigFds，无需第二次 lookupFDSelect）。
|
||||
* 单 FD 用格式 0（最省，1+numGlyphs 字节）；多 FD 用格式 3 ranges（与原始 CID 字体一致，兼容 OTS 严格校验）。 */
|
||||
const newGidToFd: number[] = new Array(newSubsetNumGlyphs);
|
||||
@ -485,8 +796,8 @@ export function subsetCFF(cffBytes: Uint8Array, subsetGids: number[]): Uint8Arra
|
||||
/** 先 patch 各唯一 Private DICT：op19 指向新 DICT 长度（Local Subr 紧跟其后） */
|
||||
const curPatchedPriv: { dict: Uint8Array; subr: Uint8Array | null }[] = [];
|
||||
for (const pi of uniquePrivInfos) {
|
||||
const patchedPriv = patchPrivateDict(b, pi.origOff, pi.len, pi.localSubr !== null);
|
||||
curPatchedPriv.push({ dict: patchedPriv, subr: pi.localSubr });
|
||||
const patchedPriv = patchPrivateDict(b, pi.origOff, pi.len, pi.newLocalSubr !== null);
|
||||
curPatchedPriv.push({ dict: patchedPriv, subr: pi.newLocalSubr });
|
||||
}
|
||||
/** patched 私有段总长（含各自 Local Subr） */
|
||||
let curPrivTotal = 0;
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user