Dynamic OG images for docs pages

.gitignore

@@ -46,3 +46,6 @@ public/rss.xml
 
 # worktrees
 .worktrees/
+
+# Generated OG images (scripts/generateOgImages.mjs)
+public/images/og/

package.json

@@ -7,7 +7,7 @@
     "analyze": "ANALYZE=true next build",
     "dev": "next-remote-watch ./src/content",
     "prebuild:rsc": "node scripts/buildRscWorker.mjs",
-    "build": "node scripts/buildRscWorker.mjs && next build && node --experimental-modules ./scripts/downloadFonts.mjs",
+    "build": "node scripts/buildRscWorker.mjs && next build && node --experimental-modules ./scripts/downloadFonts.mjs && node ./scripts/generateOgImages.mjs",
     "lint": "next lint && eslint \"src/content/**/*.md\"",
     "lint:fix": "next lint --fix && eslint \"src/content/**/*.md\" --fix",
     "format:source": "prettier --config .prettierrc --write \"{plugins,src}/**/*.{js,ts,jsx,tsx,css}\"",
@@ -51,6 +51,7 @@
     "@babel/plugin-transform-modules-commonjs": "^7.18.6",
     "@babel/preset-react": "^7.18.6",
     "@mdx-js/mdx": "^2.1.3",
+    "@resvg/resvg-js": "^2.6.2",
     "@types/body-scroll-lock": "^2.6.1",
     "@types/classnames": "^2.2.10",
     "@types/debounce": "^1.2.1",
@@ -102,6 +103,7 @@
     "retext": "^7.0.1",
     "retext-smartypants": "^4.0.0",
     "rss": "^1.2.2",
+    "satori": "^0.26.0",
     "tailwindcss": "^3.4.1",
     "typescript": "^5.7.2",
     "unist-util-visit": "^2.0.3",

scripts/generateOgImages.mjs

@@ -0,0 +1,208 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// Generates a static OG image for every content page, so social
+// cards show the page title without any runtime image generation.
+// Run after `next build` (see the `build` script in package.json).
+
+import fs from 'fs';
+import path from 'path';
+import satori from 'satori';
+import {Resvg} from '@resvg/resvg-js';
+import matter from 'gray-matter';
+
+const ROOT = process.cwd();
+const CONTENT_DIR = path.join(ROOT, 'src', 'content');
+const OUT_DIR = path.join(ROOT, 'public', 'images', 'og');
+const CONCURRENCY = 8;
+
+const bold = fs.readFileSync(
+  path.join(ROOT, 'public', 'fonts', 'Optimistic_Display_W_Bd.ttf')
+);
+const medium = fs.readFileSync(
+  path.join(ROOT, 'public', 'fonts', 'Optimistic_Display_W_Md.ttf')
+);
+
+function el(type, style, children) {
+  return {type, props: {style, children}};
+}
+
+function card(title, pagePath) {
+  const footer = ('react.dev' + pagePath).toUpperCase();
+  const logo = {
+    type: 'svg',
+    props: {
+      width: 80,
+      height: 72,
+      viewBox: '-10.5 -9.45 21 18.9',
+      fill: 'none',
+      children: [
+        {type: 'circle', props: {cx: 0, cy: 0, r: 2, fill: '#58c4dc'}},
+        {
+          type: 'g',
+          props: {
+            stroke: '#58c4dc',
+            strokeWidth: 1,
+            fill: 'none',
+            children: [
+              {type: 'ellipse', props: {rx: 10, ry: 4.5}},
+              {
+                type: 'ellipse',
+                props: {rx: 10, ry: 4.5, transform: 'rotate(60)'},
+              },
+              {
+                type: 'ellipse',
+                props: {rx: 10, ry: 4.5, transform: 'rotate(120)'},
+              },
+            ],
+          },
+        },
+      ],
+    },
+  };
+  return el(
+    'div',
+    {
+      width: '100%',
+      height: '100%',
+      display: 'flex',
+      flexDirection: 'column',
+      padding: '72px 80px',
+      backgroundColor: '#23272f',
+      backgroundImage:
+        'radial-gradient(circle at 25% 30%, #343a46 0%, #23272f 55%)',
+    },
+    [
+      el('div', {display: 'flex', alignItems: 'center', gap: '20px'}, [
+        logo,
+        el(
+          'div',
+          {
+            fontSize: 48,
+            fontFamily: 'Optimistic Display Bold',
+            color: '#f6f7f9',
+          },
+          'React'
+        ),
+      ]),
+      el(
+        'div',
+        {
+          marginTop: 'auto',
+          marginBottom: 'auto',
+          fontSize: title.length > 24 ? 72 : 96,
+          fontFamily: 'Optimistic Display Bold',
+          color: '#f6f7f9',
+          lineHeight: 1.1,
+          wordBreak: 'break-word',
+        },
+        title
+      ),
+      el(
+        'div',
+        {
+          fontSize: 28,
+          fontFamily: 'Optimistic Display Medium',
+          color: '#99a1b3',
+          letterSpacing: '0.08em',
+        },
+        footer
+      ),
+    ]
+  );
+}
+
+async function renderCard(title, pagePath) {
+  const svg = await satori(card(title, pagePath), {
+    width: 1200,
+    height: 630,
+    fonts: [
+      {
+        name: 'Optimistic Display Bold',
+        data: bold,
+        weight: 700,
+        style: 'normal',
+      },
+      {
+        name: 'Optimistic Display Medium',
+        data: medium,
+        weight: 500,
+        style: 'normal',
+      },
+    ],
+  });
+  return new Resvg(svg, {fitTo: {mode: 'width', value: 1200}}).render().asPng();
+}
+
+function collectSidebarTitles() {
+  const titles = new Map();
+  for (const name of fs.readdirSync(path.join(ROOT, 'src'))) {
+    if (!/^sidebar.*\.json$/.test(name)) continue;
+    const walk = (node) => {
+      if (node.path && node.title) {
+        titles.set(node.path, node.title);
+      }
+      for (const child of node.routes ?? []) walk(child);
+    };
+    walk(JSON.parse(fs.readFileSync(path.join(ROOT, 'src', name), 'utf8')));
+  }
+  return titles;
+}
+
+const sidebarTitles = collectSidebarTitles();
+
+function collectPages(dir, out) {
+  for (const entry of fs.readdirSync(dir, {withFileTypes: true})) {
+    const full = path.join(dir, entry.name);
+    if (entry.isDirectory()) {
+      collectPages(full, out);
+    } else if (entry.name.endsWith('.md')) {
+      const rel = path.relative(CONTENT_DIR, full).replace(/\.md$/, '');
+      const segments = rel.split(path.sep);
+      if (segments[segments.length - 1] === 'index') {
+        segments.pop();
+      }
+      const pagePath = '/' + segments.join('/');
+      const {data} = matter(fs.readFileSync(full, 'utf8'));
+      const title = data.title ?? sidebarTitles.get(pagePath);
+      if (title) {
+        out.push({title: String(title), pagePath});
+      }
+    }
+  }
+  return out;
+}
+
+export function ogImageFileName(pagePath) {
+  return pagePath.replace(/^\//, '').replace(/\//g, '-') + '.png';
+}
+
+async function main() {
+  const pages = collectPages(CONTENT_DIR, []);
+  fs.mkdirSync(OUT_DIR, {recursive: true});
+  let done = 0;
+  const queue = [...pages];
+  async function worker() {
+    for (;;) {
+      const page = queue.shift();
+      if (!page) return;
+      const png = await renderCard(page.title, page.pagePath);
+      fs.writeFileSync(path.join(OUT_DIR, ogImageFileName(page.pagePath)), png);
+      done++;
+      if (done % 100 === 0) {
+        console.log(`og-images: ${done}/${pages.length}`);
+      }
+    }
+  }
+  await Promise.all(Array.from({length: CONCURRENCY}, worker));
+  console.log(`og-images: generated ${done} images in public/images/og`);
+}
+
+main().catch((error) => {
+  console.error(error);
+  process.exit(1);
+});

src/components/Layout/Page.tsx

@@ -129,7 +129,14 @@ export function Page({
         title={title}
         titleForTitleTag={meta.titleForTitleTag}
         isHomePage={isHomePage}
-        image={`/images/og-` + section + '.png'}
+        image={
+          // OG images are generated per page at build time by
+          // scripts/generateOgImages.mjs. Error pages have dynamic
+          // titles, so they keep the static section image.
+          isHomePage || !title || cleanedPath.startsWith('/errors')
+            ? `/images/og-` + section + '.png'
+            : `/images/og/${cleanedPath.slice(1).replace(/\//g, '-')}.png`
+        }
         searchOrder={searchOrder}
       />
       {(isHomePage || isBlogIndex) && (