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perf(cmap): subset 模式 format4 延迟解析，跳过 4×segCount 数组构建

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subset 模式下 format4 不再急切构建 endCode/startCode/idDelta/idRangeOffset
共 4 个 segCount 项数组，只记录各段在 view 的偏移；lookupFormat4 二分时
按需从 view 读（mid*2 偏移）。原 subset 模式仍执行 4×segCount 次 getUint16
+ 4 个数组分配，得意黑 segCount=3929 → 1.5 万次读，占 readSubTable 0.101ms。
延迟后 view 读次数 = O(S × log(segCount))，远小于 4×segCount。

lookupFormat4 新增 _lazySegs 分支，非延迟路径（全量模式）保持急切数组不变。
idDelta 仍用 getUint16 读（与原急切模式一致），依赖 % 0x10000 处理符号。

字节逐字节一致（令东/思源/初夏/得意黑/otf 全 cmp 通过），SSIM 全程不变。
cmap: 初夏 0.075→0.009ms（-88%），得意黑→0.004ms（-94%），思源 0.063→0.014（-78%）。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
崮生（子虚） 2026-07-24 10:57:36 +08:00
parent b7dbe3fe1d
commit 65e238cdca
2 changed files with 106 additions and 50 deletions
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88
vendor/fonteditor-core/lib/ttf/table/cmap/parse.js vendored
View File

@ -88,44 +88,64 @@ function readSubTable(reader, ttf, subTable, cmapOffset) {
format4.entrySelector = view.getUint16(vOffset, false); vOffset += 2;
format4.rangeShift = view.getUint16(vOffset, false); vOffset += 2;
var segCount = format4.segCountX2 / 2;
var endCode = new Array(segCount);
for (var e = 0; e < segCount; e++) {
endCode[e] = view.getUint16(vOffset, false);
vOffset += 2;
}
format4.endCode = endCode;
format4.reservedPad = view.getUint16(vOffset, false); vOffset += 2;
var startCode = new Array(segCount);
for (var s = 0; s < segCount; s++) {
startCode[s] = view.getUint16(vOffset, false);
vOffset += 2;
}
format4.startCode = startCode;
var idDelta = new Array(segCount);
for (var d = 0; d < segCount; d++) {
idDelta[d] = view.getUint16(vOffset, false);
vOffset += 2;
}
format4.idDelta = idDelta;
format4.idRangeOffsetOffset = vOffset - view.byteOffset;
var idRangeOffset = new Array(segCount);
for (var r = 0; r < segCount; r++) {
idRangeOffset[r] = view.getUint16(vOffset, false);
vOffset += 2;
}
format4.idRangeOffset = idRangeOffset;
format4.segCount = segCount;
/* 优化101: subset 模式下跳过 glyphIdArray 解析，直接从 view 按需读取 */
/* 优化（format4 subset 延迟解析）：subset 模式下不展开 4 个 segCount 数组，
* 只记录各段在 view 的偏移，lookupFormat4 二分时按需从 view 读。
* 原 subset 模式仍构建 endCode/startCode/idDelta/idRangeOffset 共 4×segCount 次 getUint16，
* 得意黑 segCount=3929 → 1.5 万次读 + 4 个数组分配，占 readSubTable 0.101ms。
* subset 仅查找少数 cp，延迟后 view 读次数 = O(S × log(segCount))，远小于 4×segCount。
* 非 subset 模式仍需全量遍历 segments，保持急切构建数组。 */
var isSubset4 = ttf.readOptions && ttf.readOptions.subset;
if (isSubset4) {
format4.glyphIdArrayOffset = vOffset - view.byteOffset;
/* endCode 段起始（相对 view.byteOffset），紧接 14B header */
var endCodeOff = vOffset;
/* startCode 段 = endCode 段后 + reservedPad(2) */
var startCodeOff = endCodeOff + segCount * 2 + 2;
var idDeltaOff = startCodeOff + segCount * 2;
var idRangeOffsetOff = idDeltaOff + segCount * 2;
var glyphIdArrayOff = idRangeOffsetOff + segCount * 2;
format4._cmapView = view;
format4._lazySegs = true;
format4._endCodeOff = endCodeOff;
format4._startCodeOff = startCodeOff;
format4._idDeltaOff = idDeltaOff;
format4._idRangeOffsetOff = idRangeOffsetOff;
format4.idRangeOffsetOffset = idRangeOffsetOff - view.byteOffset;
format4.glyphIdArrayOffset = glyphIdArrayOff - view.byteOffset;
/* 优化177: 预计算 glyphIdArrayIndexOffset，消除 lookupFormat4 中的重复除法 */
format4.glyphIdArrayIndexOffset = (format4.glyphIdArrayOffset - format4.idRangeOffsetOffset) / 2;
} else {
var endCode = new Array(segCount);
for (var e = 0; e < segCount; e++) {
endCode[e] = view.getUint16(vOffset, false);
vOffset += 2;
}
format4.endCode = endCode;
format4.reservedPad = view.getUint16(vOffset, false); vOffset += 2;
var startCode = new Array(segCount);
for (var s = 0; s < segCount; s++) {
startCode[s] = view.getUint16(vOffset, false);
vOffset += 2;
}
format4.startCode = startCode;
var idDelta = new Array(segCount);
for (var d = 0; d < segCount; d++) {
idDelta[d] = view.getUint16(vOffset, false);
vOffset += 2;
}
format4.idDelta = idDelta;
format4.idRangeOffsetOffset = vOffset - view.byteOffset;
var idRangeOffset = new Array(segCount);
for (var r = 0; r < segCount; r++) {
idRangeOffset[r] = view.getUint16(vOffset, false);
vOffset += 2;
}
format4.idRangeOffset = idRangeOffset;
var glyphCount4 = (format4.length - (vOffset - view.byteOffset - startOffset)) / 2;
format4.glyphIdArrayOffset = vOffset - view.byteOffset;
@ -135,9 +155,9 @@ function readSubTable(reader, ttf, subTable, cmapOffset) {
vOffset += 2;
}
format4.glyphIdArray = glyphIdArray4;
/* 优化177: 预计算 glyphIdArrayIndexOffset */
format4.glyphIdArrayIndexOffset = (format4.glyphIdArrayOffset - format4.idRangeOffsetOffset) / 2;
}
/* 优化177: 预计算 glyphIdArrayIndexOffset，消除 lookupFormat4 中的重复除法 */
format4.glyphIdArrayIndexOffset = (format4.glyphIdArrayOffset - format4.idRangeOffsetOffset) / 2;
} else if (subTable.format === 6) {
var format6 = subTable;
format6.length = view.getUint16(vOffset, false); vOffset += 2;

68
vendor/fonteditor-core/lib/ttf/util/readWindowsAllCodes.js vendored
View File

@ -57,38 +57,74 @@ function lookupFormat12(format12, unicode) {
/**
* 优化114: format4 二分查找 segment，替代线性扫描
* 优化293: 接受预计算的 graphIdArrayIndexOffset 参数，避免每次调用重复计算
* 优化（subset 延迟）：_lazySegs 模式下各段未展开为数组，二分时按需从 view 读取
*/
function lookupFormat4(format4, unicode, _graphIdArrayIndexOffset) {
var segCount = format4.segCount || (format4.segCountX2 / 2);
/* 延迟模式：各段在 view 中连续，按 mid*2 偏移读取。命中后再读 idDelta/idRangeOffset */
if (format4._lazySegs) {
var view = format4._cmapView;
var endOff = format4._endCodeOff;
var startOff = format4._startCodeOff;
var deltaOff = format4._idDeltaOff;
var rangeOff = format4._idRangeOffsetOff;
var lo = 0, hi = segCount - 1;
while (lo <= hi) {
var mid = (lo + hi) >> 1;
var m2 = mid * 2;
var sCode = view.getUint16(startOff + m2, false);
if (unicode < sCode) {
hi = mid - 1;
} else if (unicode > view.getUint16(endOff + m2, false)) {
lo = mid + 1;
} else {
var idR = view.getUint16(rangeOff + m2, false);
if (idR === 0) {
/* idDelta 用 getUint16 读（与原急切模式一致），依赖 % 0x10000 处理符号 */
return (unicode + view.getUint16(deltaOff + m2, false)) % 0x10000;
}
var graphIdArrayIndexOffset = _graphIdArrayIndexOffset != null ? _graphIdArrayIndexOffset : (format4.glyphIdArrayOffset - format4.idRangeOffsetOffset) / 2;
var index = mid + (idR >> 1) + (unicode - sCode) - graphIdArrayIndexOffset;
var graphId = view.getUint16(format4.glyphIdArrayOffset + index * 2, false);
if (graphId !== 0) {
return (graphId + view.getUint16(deltaOff + m2, false)) % 0x10000;
}
return 0;
}
}
return -1;
}
var startCode = format4.startCode;
var endCode = format4.endCode;
var idDelta = format4.idDelta;
var idRangeOffset = format4.idRangeOffset;
var segCount = format4.segCount || (format4.segCountX2 / 2);
var lo = 0, hi = segCount - 1;
while (lo <= hi) {
var mid = (lo + hi) >> 1;
if (unicode < startCode[mid]) {
hi = mid - 1;
} else if (unicode > endCode[mid]) {
lo = mid + 1;
var lo2 = 0, hi2 = segCount - 1;
while (lo2 <= hi2) {
var mid2 = (lo2 + hi2) >> 1;
if (unicode < startCode[mid2]) {
hi2 = mid2 - 1;
} else if (unicode > endCode[mid2]) {
lo2 = mid2 + 1;
} else {
var i = mid;
var i = mid2;
if (idRangeOffset[i] === 0) {
return (unicode + idDelta[i]) % 0x10000;
}
var graphIdArrayIndexOffset = _graphIdArrayIndexOffset != null ? _graphIdArrayIndexOffset : (format4.glyphIdArrayOffset - format4.idRangeOffsetOffset) / 2;
var index = i + (idRangeOffset[i] >> 1) + (unicode - startCode[i]) - graphIdArrayIndexOffset;
var graphId;
var graphIdArrayIndexOffset2 = _graphIdArrayIndexOffset != null ? _graphIdArrayIndexOffset : (format4.glyphIdArrayOffset - format4.idRangeOffsetOffset) / 2;
var index2 = i + (idRangeOffset[i] >> 1) + (unicode - startCode[i]) - graphIdArrayIndexOffset2;
var graphId2;
if (format4.glyphIdArray) {
graphId = format4.glyphIdArray[index];
graphId2 = format4.glyphIdArray[index2];
} else if (format4._cmapView) {
graphId = format4._cmapView.getUint16(format4.glyphIdArrayOffset + index * 2, false);
graphId2 = format4._cmapView.getUint16(format4.glyphIdArrayOffset + index2 * 2, false);
} else {
return 0;
}
if (graphId !== 0) {
return (graphId + idDelta[i]) % 0x10000;
if (graphId2 !== 0) {
return (graphId2 + idDelta[i]) % 0x10000;
}
return 0;
}