perf: embed only used fonts

src/embed-webfonts.ts

@@ -202,16 +202,46 @@
   return getWebFontRules(cssRules)
 }
 
+function normalizeFontFamily(font: string) {
+  return font.trim().replace(/["']/g, '')
+}
+
+function getUsedFonts(node: HTMLElement) {
+  const fonts = new Set<string>()
+  function traverse(node: HTMLElement) {
+    const fontFamily =
+      node.style.fontFamily || getComputedStyle(node).fontFamily
+    fontFamily.split(',').forEach((font) => {
+      fonts.add(normalizeFontFamily(font))
+    })
+
+    Array.from(node.children).forEach((child) => {
+      if (child instanceof HTMLElement) {
+        traverse(child)
+      }
+    })
+  }
+  traverse(node)
+  return fonts
+}
+
 export async function getWebFontCSS<T extends HTMLElement>(
   node: T,
   options: Options,
 ): Promise<string> {
   const rules = await parseWebFontRules(node, options)
+  const usedFonts = getUsedFonts(node)
   const cssTexts = await Promise.all(
-    rules.map((rule) => {
-      const baseUrl = rule.parentStyleSheet ? rule.parentStyleSheet.href : null
-      return embedResources(rule.cssText, baseUrl, options)
-    }),
+    rules
+      .filter((rule) =>
+        usedFonts.has(normalizeFontFamily(rule.style.fontFamily)),
+      )
+      .map((rule) => {
+        const baseUrl = rule.parentStyleSheet
+          ? rule.parentStyleSheet.href
+          : null
+        return embedResources(rule.cssText, baseUrl, options)
+      }),
   )
 
   return cssTexts.join('\n')

test/resources/fonts/web-fonts/empty.html

@@ -0,0 +1 @@
+<div style="font-family: Font1"></div>

test/spec/webfont.spec.ts

@@ -0,0 +1,107 @@
+import * as htmlToImage from '../../src'
+import { getSvgDocument } from './helper'
+
+describe('font embedding', () => {
+  describe('should embed only used fonts', () => {
+    it('should embed 1 font when use 1', async () => {
+      const root = document.createElement('div')
+      document.body.append(root)
+      try {
+        root.innerHTML = `
+          <style>
+              @font-face { 
+                  font-family: 'Font 0';
+                  src: url('https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu72xKKTU1Kvnz.woff2');
+              }
+              @font-face { 
+                  font-family: 'Font 1';
+                  src: url('https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu72xKKTU1Kvnz.woff2');
+              }
+              @font-face { 
+                  font-family: 'Font 2';
+                  src: url('https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu72xKKTU1Kvnz.woff2');
+              }
+          </style>
+          <p style="font-family: 'Font 1'">Hello world</p>
+        `
+        const svg = await htmlToImage.toSvg(root)
+        const doc = await getSvgDocument(svg)
+        const [style] = Array.from(doc.getElementsByTagName('style'))
+        expect(style.textContent).toContain('Font 1')
+        expect(style.textContent).not.toContain('Font 0')
+        expect(style.textContent).not.toContain('Font 2')
+      } finally {
+        root.remove()
+      }
+    })
+    it('should embed 2 fonts when use 2', async () => {
+      const root = document.createElement('div')
+      document.body.append(root)
+      try {
+        root.innerHTML = `
+          <style>
+              @font-face { 
+                  font-family: 'Font 0';
+                  src: url('https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu72xKKTU1Kvnz.woff2');
+              }
+              @font-face { 
+                  font-family: 'Font 1';
+                  src: url('https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu72xKKTU1Kvnz.woff2');
+              }
+              @font-face { 
+                  font-family: 'Font 2';
+                  src: url('https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu72xKKTU1Kvnz.woff2');
+              }
+          </style>
+          <p style="font-family: 'Font 0'">Hello world</p>
+          <p style="font-family: 'Font 2'">Hello world</p>
+        `
+        const svg = await htmlToImage.toSvg(root)
+        const doc = await getSvgDocument(svg)
+        const [style] = Array.from(doc.getElementsByTagName('style'))
+        expect(style.textContent).toContain('Font 0')
+        expect(style.textContent).toContain('Font 2')
+        expect(style.textContent).not.toContain('Font 1')
+      } finally {
+        root.remove()
+      }
+    })
+    it('should embed font used by deeply nested child', async () => {
+      const root = document.createElement('div')
+      document.body.append(root)
+      try {
+        root.innerHTML = `
+          <style>
+              @font-face { 
+                  font-family: 'Font 0';
+                  src: url('https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu72xKKTU1Kvnz.woff2');
+              }
+              @font-face { 
+                  font-family: 'Font 1';
+                  src: url('https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu72xKKTU1Kvnz.woff2');
+              }
+              @font-face { 
+                  font-family: 'Font 2';
+                  src: url('https://fonts.gstatic.com/s/roboto/v30/KFOmCnqEu92Fr1Mu72xKKTU1Kvnz.woff2');
+              }
+          </style>
+          <div>
+            <div>
+                <div>
+                    <div style="font-family: 'Font 1'">Hello world</div>
+                </div>
+            </div>
+          </div>
+        `
+        const svg = await htmlToImage.toSvg(root)
+        const doc = await getSvgDocument(svg)
+        const [style] = Array.from(doc.getElementsByTagName('style'))
+        expect(style.textContent).toContain('Font 1')
+        expect(style.textContent).not.toContain('Font 0')
+        expect(style.textContent).not.toContain('Font 2')
+      } finally {
+        root.remove()
+      }
+    })
+  })
+})