cc9a6db853
Ref: #1379 This takes a naive approach to font-width computation, the most compute-intensive part of rendering badges. 1. Add the widths of the individual characters. - These widths are measured on startup using PDFKit. 2. For each character pair, add a kerning adjustment - The difference between the width of each character pair, and the sum of the characters' separate widths. - These are computed for each character pair on startup using PDFKit. 3. For a string with characters outside the printable ASCII character set, fall back to PDFKit. This branch averaged 0.041 ms in `makeBadge`, compared to 0.144 ms on master, a speedup of 73%. That was on a test of 10,000 consecutive requests (using the `benchmark-performance.sh` script, now checked in). The speedup applies to badges containing exclusively printable ASCII characters. It wouldn't be as dramatic on non-ASCII text. Though, we could add some frequently used non-ASCII characters to the cached set.
90 lines
2.5 KiB
JavaScript
90 lines
2.5 KiB
JavaScript
'use strict';
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const PDFDocument = require('pdfkit');
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class PDFKitTextMeasurer {
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constructor(fontPath, fallbackFontPath) {
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this.document = new PDFDocument({ size: 'A4', layout: 'landscape' })
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.fontSize(11);
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try {
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this.document.font(fontPath);
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} catch(e) {
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if (fallbackFontPath) {
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console.error(`Text-width computation may be incorrect. Unable to load font at ${fontPath}. Using fallback font ${fallbackFontPath} instead.`);
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this.document.font(fallbackFontPath);
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} else {
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console.error('No fallback font set.');
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throw e;
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}
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}
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}
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widthOf(str) {
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return this.document.widthOfString(str);
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}
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}
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class QuickTextMeasurer {
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constructor(fontPath, fallbackFontPath) {
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this.baseMeasurer = new PDFKitTextMeasurer(fontPath, fallbackFontPath)
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// This will be a Map of characters -> numbers.
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this.characterWidths = new Map();
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// This will be Map of Maps of characters -> numbers.
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this.kerningPairs = new Map();
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this._prepare();
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}
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static printableAsciiCharacters() {
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const printableRange = [32, 126];
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const length = printableRange[1] - printableRange[0] + 1;
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return Array
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.from({ length }, (value, i) => printableRange[0] + i)
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.map(charCode => String.fromCharCode(charCode));
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}
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_prepare() {
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const charactersToCache = this.constructor.printableAsciiCharacters();
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charactersToCache.forEach(char => {
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this.characterWidths.set(char, this.baseMeasurer.widthOf(char));
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this.kerningPairs.set(char, new Map());
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});
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charactersToCache.forEach(first => {
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charactersToCache.forEach(second => {
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const individually = this.characterWidths.get(first) + this.characterWidths.get(second);
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const asPair = this.baseMeasurer.widthOf(`${first}${second}`);
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const kerningAdjustment = asPair - individually;
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this.kerningPairs.get(first).set(second, kerningAdjustment);
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});
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});
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}
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widthOf(str) {
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const { characterWidths, kerningPairs } = this;
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let result = 0;
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let previous = null;
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for (const character of str) {
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if (!characterWidths.has(character)) {
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// Bail.
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return this.baseMeasurer.widthOf(str);
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}
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result += characterWidths.get(character);
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if (previous !== null) {
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result += kerningPairs.get(previous).get(character);
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}
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previous = character;
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}
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return result;
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}
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}
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module.exports = {
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PDFKitTextMeasurer,
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QuickTextMeasurer,
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};
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