feat: add ability to add text stroke (#645)

![af8e1b7b-0c8a-4722-833c-df1b38b0df26](https://github.com/user-attachments/assets/af7d0862-a31e-43f9-9415-acab1ea98dd5)

This PR is adding ability to stroke to texts.

fixes: #578 

Added 2 properties (`WebkitTextStrokeWidth`, `WebkitTextStrokeColor`)
and 1 shorthands (`WebkitTextStroke`). When stroke is enabled,
`paint-order: stroke;` and `stroke-linejoin: round;` are automatically
set to prevent the stroke from obscuring the text.

I don't have a deep understanding of all the code so further
improvements may be needed.

README.md

@@ -270,6 +270,18 @@ Satori uses the same Flexbox [layout engine](https://yogalayout.com) as React Na
 <tr><td><code>maskSize</code></td><td>Support two-value size i.e. `10px 20%`</td><td><a href="https://og-playground.vercel.app/?share=pVLfb9MwEP5XLEvLhpQ2P0a3LlpAAiYxJEATk_rSF8e-JNc6drAd2lD1f8duV8H6yoN19ved7j7ffTvKtQBa0HuBv5aKEOtGCeVuF-6EtIBN6wpymaXpxWV8BDcoXHuGCbS9ZKNHawnbExrun9AAd6iV57iWQ6dOLJPYqEcHnQ0UKAfmRK0G67AeP2oPqtD_NV17_Af-hoJc5_9Aixe1N2n6glaMrxujByV8jcHIq9a53hZJgh1rwE4HFWTbdsp1l_StdnqSzfJ5Pr-9e5tnt9mkruD6ZiYyccf4e9xKrEpTTbJpPs2in-V8FtVdueqbiBvdl16jD2O0KbM8TSNuS2uaKsItihLGLy3__KFmiyf8vnpIvz03s_rpzelHHbPrx6DJ6zRMIJOTJkRf8oqj4RIIc2SWXoQTk0oOEBNnmNfPjE96Veg4Gr-ffkvyvztaQLVG9_X_O5EkOWzID90QAzV4nANBRVrXyfNm52oCv98v1buluk-863ykMdV98IilxY4e_EWLMMOYHh1Ii7BTKqAaGlrUTFqIKXR6hc9jH-zrNoeXLxSM8NBVIGjhzAD7mDpW-YwWpNQbbaSg-z8">Example</a></td></tr>
 <tr><td><code>maskRepeat</code></td><td><code>repeat</code>, <code>repeat-x</code>, <code>repeat-y</code>, <code>no-repeat</code>, defaults to <code>repeat</code></td><td><a href="https://og-playground.vercel.app/?share=nVbpjqNIEn6VkqXVzMg1AhtjQ-3MStwGA-Ywl9U_hssJ5jSHAbf63TdxdfXUzh4_FhllHF8cGZkm4usirKJ48bb4LUrvX8qXl7ab8vj3r19n-uUliVOQdG8vP61Q9G8_vb4LhzTqkr_IorStc3-C0ksejx_SmWbTJg67tCqhLqzyvig_tH6eglLs4qKdVXHZxc2H6tq3XXqZmAoKyzn-v6ovUG6mj_jtBVt_Ejnfs92i6Hdp4IcZaKq-jKCPvsl_jvzOf0sLH8RIXYK_B34bbzevqU0fjQE9CKCi4KOaVsJZAFK0PvMaQ3lwYbPiSNqzgHJV00BFqmk34XaGiEbucHlxslDqMNtRAJpyJkUpM0NTFAcXzqco6ztPUSbggs-8BTgY_AMvwl9UU9Qz_lPvPP0-WaiEz6zinkKoPwLIs9_lkGcATGEO-o6jTUANn3iKeJJ2F-6CJ58PJp8_ICFzA7QeFZqSbqHwBOW1zSeow62UY6HeAxNPzgKZnk18E7jfU2LHzbFMulBY5ZHAgVhYtUGpbGMWTT3HuHuFtZ35wLFRzyRScQ-2EDNEQkuKeaJaDM0GmJSLrNcrzGYQr5uDyFBA20vZ-VqbBuf98BkWRqGZUhXtjeGYEvcIizC5DB9yQU7niRiPpwyXH9QkP8RJdqF9unrEDo56Luig_fXD9yf_3NlVr2GRw3zye5DS01nwtp4j3SNXJ8VU_IH_eD9ygfjifEVTf2-gIVvd5TUO8-CzYC3l8rNWJOo750J-cHBfRKqB6rMf4t2-1mDsPCiN5Bn_uhk15t3umJGT79h9JPCQJ_tP9oSM_YfcP-rGwFrAPViZIUAbiH2v97P-p81BsHcJDc-ZWvGSwfHWkRZUm-8UDuWsMsJM7ITXvl8YYxpVaWIcDFuQMp-lDYZXUyUzNVLX4KYTMBgGNxwFaEUoF84QWe6mXMYz13GVeU91ISF0sPF8oDNpbYtxHVWOmSxRzOXLyHCzEenHcHk5as7liJUdRl2SjhWUE3PZ2gdM43nDPrEUGwnJxHISvL6WuHksd8qjuK66bTDEQyKKHu5qIGNFxvAo5byyizvKZ1y7x28hf-CjZXAw2EGzWn_bP04b2lbtMx3Y0jpXaDNktVtXbPH7o8A3k8q5jhVNxsBWhe0F8jqqYqJnr17XAO9o1UZrAcDRo3tY7Zc5wGhikM4Wilz3YTH1akMOy1XMMGOVEZokexWWlo7HMrJ4mBzVqM7u8aSyN7SWb870cAKdUCqJ6c2z3xr6gV61QqrD22-O_pRosq3iHQHGzFRQ5Yisjo61Tseq0VByWxKmdVrHa9fRk122bBpiUHnDCTG_OR28OudwcW0E4qGozUaOdnHZRLesiUbXkbg1bku7lGdSrNTYBlHqgxtVdr9RjvZyd8xXd4BUYBvou7VvXLoxGkldoSrXdvmzRHnurQiLi9WfDPsgi_dJE5cB4pIZG6gaVm1qkrxQVSUqZU3d0bDMtxfdU3kSiVwJKVrPXy8HaWAJzNBDjq4entTprFOeWL32HNwX1u2dXVfSQJQeeyMecFNHn6ezUUmaO9md4uaKL3twybpTNuQ1QYGym8gitAjRu7DoFaQkWHI7miNzZ2UUsuEE2LlmjNrpp5XTh3mM-eXt_mi2O1kor9tBsfwbxgILhzkJ68PRPh25nlhRkxTTuWQq6dWVpp3BVPWq6ree34P7ivDPAljuwsQbB8fxjnTSn-lsx7sPMdwQe48zB3lI0rI02Vgz2kBmsColkI3M3QuwOSUEzZuCd99fNIykkP0YINFwL6LNUiQmKiAPoo5PqkVFGc1fEaQtxrW6psdO4C5IhRxC1916J3mrxeDerWKcRC_0etLjCiR7IexI2eG0w57VB4S0zd53hq0xZI7sNuqZ2ka4KhmHvBQke2sbO_gn013TtlADlAmPyZEcSqsdVrqFl8IbmAgqnY9pFukjifCFN1mcGPOEFPsIAi-V0rgqfdMZSlIkpEGa4ua3J44SQ4thMqQRr8ujjuxUKgCIq3Iaheg6fbOvF2qN895725IMC-eaTAIA_P77Lx_NvfDbTJw79NvLH3laxn7zK2j8KIUTwM9d9dLMPf71Jcj7-PWla_yyrf0G6n7545P9-3AwTyj1-LJaz8tn90Zcx_48VjRP4tcfSicOsrRTPmXwl6GhvYPlWOQfg4O2V9fnicZ8x0B92OyOLDWIKV2dnbz097B5XMGgMCKICnsK1_MHGk0VczNCzBp-2DG9IDeaKQ4iSwHlJEIsNSrXp49N4Ix9-PjUXGCjiyYcUyb8HhbhfcYpDPmIijDVruPguUYlCjBmho4KMzxUk6Yhpn2-zDDILNeqJ0g_LKDDWDI7v0_dKLMZpJWVyHM45NeqOazgikMfhgJt1KvVzuts66QiOBd5G8D9RuukjgQrFRliCZvOnMvyx0H8ezH_n-P808v_ONQ_Qf_laL99-1L-40v5GwLHXLguXhdVPQ-l7eLt6-I50C7eZpevi_eRd_E2D5GLKA56sHi7-Hkbvy7iorqmp6me5-VueHLQ0Tx5ckUQR4u3runjb6-Lzg8gIonzvBqqJo8W3_4J">Example</a></td></tr>
 
+<tr>
+<td rowspan="2"><code>WebkitTextStroke</code>
+<td><code>WebkitTextStrokeWidth</code></td>
+<td>Supported</td>
+<td></td>
+</tr>
+<tr>
+<td><code>WebkitTextStrokeColor</code></td>
+<td>Supported</td>
+<td></td>
+</tr>
+
 </tbody>
 </table>
 

src/builder/text.ts

@@ -132,6 +132,14 @@ export default function buildText(
     transform: matrix || undefined,
     'clip-path': clipPathId ? `url(#${clipPathId})` : undefined,
     style: style.filter ? `filter:${style.filter}` : undefined,
+    'stroke-width': style.WebkitTextStrokeWidth
+      ? `${style.WebkitTextStrokeWidth}px`
+      : undefined,
+    stroke: style.WebkitTextStrokeWidth
+      ? style.WebkitTextStrokeColor
+      : undefined,
+    'stroke-linejoin': style.WebkitTextStrokeWidth ? 'round' : undefined,
+    'paint-order': style.WebkitTextStrokeWidth ? 'stroke' : undefined,
   }
   return [
     (filter ? `${filter}<g filter="url(#satori_s-${id})">` : '') +

src/handler/expand.ts

@@ -195,6 +195,19 @@ function handleSpecialCase(
     return result
   }
 
+  if (name === 'WebkitTextStroke') {
+    value = value.toString().trim()
+    const values = value.split(' ')
+    if (values.length !== 2) {
+      throw new Error('Invalid `WebkitTextStroke` value.')
+    }
+
+    return {
+      WebkitTextStrokeWidth: purify(name, values[0]),
+      WebkitTextStrokeColor: purify(name, values[1]),
+    }
+  }
+
   return
 }
 
@@ -267,6 +280,8 @@ type MainStyle = {
   }[]
   textShadowColor: string[]
   textShadowRadius: number[]
+  WebkitTextStrokeWidth: number
+  WebkitTextStrokeColor: string
 }
 
 type OtherStyle = Exclude<Record<PropertyKey, string | number>, keyof MainStyle>

src/handler/inheritable.ts

@@ -14,6 +14,8 @@ const list = new Set([
   'textShadowOffset',
   'textShadowColor',
   'textShadowRadius',
+  'WebkitTextStrokeWidth',
+  'WebkitTextStrokeColor',
   'textDecorationLine',
   'textDecorationStyle',
   'textDecorationColor',

src/text/index.ts

@@ -734,6 +734,18 @@ export default async function* buildTextNodes(
             mask: overflowMaskId ? `url(#${overflowMaskId})` : undefined,
 
             style: cssFilter ? `filter:${cssFilter}` : undefined,
+            'stroke-width': inheritedStyle.WebkitTextStrokeWidth
+              ? `${inheritedStyle.WebkitTextStrokeWidth}px`
+              : undefined,
+            stroke: inheritedStyle.WebkitTextStrokeWidth
+              ? inheritedStyle.WebkitTextStrokeColor
+              : undefined,
+            'stroke-linejoin': inheritedStyle.WebkitTextStrokeWidth
+              ? 'round'
+              : undefined,
+            'paint-order': inheritedStyle.WebkitTextStrokeWidth
+              ? 'stroke'
+              : undefined,
           })
         : ''
 

test/webkit-text-stroke.test.tsx

@@ -0,0 +1,83 @@
+import { it, describe, expect } from 'vitest'
+
+import { initFonts, toImage } from './utils.js'
+import satori from '../src/index.js'
+
+describe('webkit-text-stroke', () => {
+  let fonts
+  initFonts((f) => (fonts = f))
+
+  it('should work basic text stroke', async () => {
+    const svg = await satori(
+      <div
+        style={{
+          width: 100,
+          height: 100,
+          fontSize: 30,
+          background: '#ebebeb',
+          color: '#ffffff',
+          WebkitTextStroke: '4px #000000',
+        }}
+      >
+        Hello, world
+      </div>,
+      { width: 100, height: 100, fonts }
+    )
+    expect(toImage(svg, 100)).toMatchImageSnapshot()
+  })
+
+  it('should work nested text stroke', async () => {
+    const svg = await satori(
+      <div
+        style={{
+          display: 'flex',
+          flexWrap: 'wrap',
+          width: 100,
+          height: 100,
+          fontSize: 30,
+          background: '#ebebeb',
+          color: '#ffffff',
+          WebkitTextStroke: '4px #000000',
+        }}
+      >
+        Hello, <span style={{ WebkitTextStrokeColor: '#ff0000' }}>world</span>
+      </div>,
+      { width: 100, height: 100, fonts }
+    )
+    expect(toImage(svg, 100)).toMatchImageSnapshot()
+  })
+
+  it('should work nested and complex text stroke', async () => {
+    const svg = await satori(
+      <div
+        style={{
+          display: 'flex',
+          flexWrap: 'wrap',
+          width: 100,
+          height: 100,
+          fontSize: 30,
+          background: '#ebebeb',
+          color: '#ffffff',
+          WebkitTextStroke: '4px #000000',
+        }}
+      >
+        Hello,
+        <span style={{ WebkitTextStrokeColor: '#f00' }}>w</span>
+        <span style={{ WebkitTextStrokeColor: '#ff0' }}>o</span>
+        <span style={{ WebkitTextStrokeColor: '#0f0' }}>r</span>
+        <span style={{ WebkitTextStrokeColor: '#0ff' }}>l</span>
+        <span style={{ WebkitTextStrokeColor: '#00f' }}>d</span>
+        <span
+          style={{
+            WebkitTextStrokeColor: '#f0f',
+            WebkitTextStrokeWidth: '6px',
+          }}
+        >
+          !
+        </span>
+      </div>,
+      { width: 100, height: 100, fonts }
+    )
+    expect(toImage(svg, 100)).toMatchImageSnapshot()
+  })
+})