feat: Multiline text overflow ellipsis (#480)

### Description
1. Support multiline text overflow ellipsis(webkit-line-clamp +
webkit-box-orient).

2. Fixed a bug where overflow: 'hidden' should not be inherited by child
elements.

3. Support the 'line-clamp' property, including custom block ellipsis.

I added display: block here because whether it's required by the CSS
draft or needed to implement this feature (must be different from
display: flex), it seems I have to do so. One thing I want to discuss
here is whether we can set the default display to flex, because this is
more in line with the original behavior of the browser and does not seem
to cause any problems (can pass all unit tests).



https://github.com/vercel/satori/assets/22126563/5ec006a7-9cfb-4fc4-9000-adc9fb042c17


https://github.com/vercel/satori/assets/22126563/d672942e-e2c9-423c-8bcf-23a932e7cfb3


Closes: #253

---------

Co-authored-by: Shu Ding <[email protected]>

src/characters.ts

@@ -6,3 +6,4 @@ export function stringFromCode(code: string): string {
 
 export const Space = stringFromCode('U+0020')
 export const Tab = stringFromCode('U+0009')
+export const HorizontalEllipsis = stringFromCode('U+2026')

src/handler/index.ts

@@ -175,7 +175,9 @@ export default async function handler(
       style.display,
       {
         flex: Yoga.DISPLAY_FLEX,
+        block: Yoga.DISPLAY_FLEX,
         none: Yoga.DISPLAY_NONE,
+        '-webkit-box': Yoga.DISPLAY_FLEX,
       },
       Yoga.DISPLAY_FLEX,
       'display'

src/text.ts

@@ -14,15 +14,17 @@ import {
   isUndefined,
   isString,
   lengthToNumber,
+  isNumber,
 } from './utils.js'
 import buildText, { container } from './builder/text.js'
 import { buildDropShadow } from './builder/shadow.js'
 import buildDecoration from './builder/text-decoration.js'
 import { Locale } from './language.js'
 import { FontEngine } from './font.js'
-import { Space, Tab } from './characters.js'
+import { HorizontalEllipsis, Space, Tab } from './characters.js'
 
 const skippedWordWhenFindingMissingFont = new Set([Tab])
+
 function shouldSkipWhenFindingMissingFont(word: string): boolean {
   return skippedWordWhenFindingMissingFont.has(word)
 }
@@ -49,7 +51,6 @@ export default async function* buildTextNodes(
 
   const {
     textAlign,
-    textOverflow,
     whiteSpace,
     wordBreak,
     lineHeight,
@@ -74,6 +75,11 @@ export default async function* buildTextNodes(
     wordBreak as string
   )
 
+  const [lineLimit, blockEllipsis] = processTextOverflow(
+    parentStyle,
+    allowSoftWrap
+  )
+
   const textContainer = createTextContainerNode(Yoga, textAlign as string)
   parent.insertChild(textContainer, parent.getChildCount())
 
@@ -222,7 +228,7 @@ export default async function* buildTextNodes(
     // @TODO: Support different writing modes.
     // @TODO: Support RTL languages.
     let i = 0
-    while (i < words.length) {
+    while (i < words.length && lines < lineLimit) {
       let word = words[i]
       const forceBreak = requiredBreaks[i]
 
@@ -373,10 +379,12 @@ export default async function* buildTextNodes(
     }
 
     if (currentWidth) {
+      if (lines < lineLimit) {
+        height += currentLineHeight
+      }
       lines++
       lineWidths.push(currentWidth)
       baselines.push(currentBaselineOffset)
-      height += currentLineHeight
     }
 
     // @TODO: Support `line-height`.
@@ -482,15 +490,14 @@ export default async function* buildTextNodes(
   let mergedPath = ''
   let extra = ''
   let skippedLine = -1
-  let ellipsisWidth = textOverflow === 'ellipsis' ? measureGrapheme('…') : 0
-  let spaceWidth = textOverflow === 'ellipsis' ? measureGrapheme(' ') : 0
   let decorationLines: Record<number, null | number[]> = {}
   let wordBuffer: string | null = null
   let bufferedOffset = 0
 
   for (let i = 0; i < texts.length; i++) {
     // Skip whitespace and empty characters.
     const layout = wordPositionInLayout[i]
+    const nextLayout = wordPositionInLayout[i + 1]
 
     if (!layout) continue
 
@@ -538,34 +545,80 @@ export default async function* buildTextNodes(
       ]
     }
 
-    if (textOverflow === 'ellipsis') {
-      if (lineWidths[line] > parentContainerInnerWidth) {
+    if (lineLimit !== Infinity) {
+      let _blockEllipsis = blockEllipsis
+      let ellipsisWidth = measureGrapheme(blockEllipsis)
+      if (ellipsisWidth > parentContainerInnerWidth) {
+        _blockEllipsis = HorizontalEllipsis
+        ellipsisWidth = measureGrapheme(_blockEllipsis)
+      }
+      const spaceWidth = measureGrapheme(Space)
+      const isNotLastLine = line < lineWidths.length - 1
+      const isLastAllowedLine = line + 1 === lineLimit
+
+      function calcEllipsis(baseWidth: number, _text: string) {
+        const chars = segment(_text, 'grapheme', locale)
+
+        let subset = ''
+        let resolvedWidth = 0
+
+        for (const char of chars) {
+          const w = baseWidth + measureGraphemeArray([subset + char])
+          if (
+            // Keep at least one character:
+            // > The first character or atomic inline-level element on a line
+            // must be clipped rather than ellipsed.
+            // https://drafts.csswg.org/css-overflow/#text-overflow
+            subset &&
+            w + ellipsisWidth > parentContainerInnerWidth
+          ) {
+            break
+          }
+          subset += char
+          resolvedWidth = w
+        }
+
+        return {
+          subset,
+          resolvedWidth,
+        }
+      }
+
+      if (
+        isLastAllowedLine &&
+        (isNotLastLine || lineWidths[line] > parentContainerInnerWidth)
+      ) {
         if (
-          layout.x + width + ellipsisWidth + spaceWidth >
+          leftOffset + width + ellipsisWidth + spaceWidth >
           parentContainerInnerWidth
         ) {
-          const chars = segment(text, 'grapheme', locale)
-          let subset = ''
-          let resolvedWidth = 0
-          for (const char of chars) {
-            const w = layout.x + measureGraphemeArray([subset + char])
-            if (
-              // Keep at least one character:
-              // > The first character or atomic inline-level element on a line
-              // must be clipped rather than ellipsed.
-              // https://drafts.csswg.org/css-overflow/#text-overflow
-              subset &&
-              w + ellipsisWidth > parentContainerInnerWidth
-            ) {
-              break
-            }
-            subset += char
-            resolvedWidth = w
-          }
-          text = subset + '…'
+          const { subset, resolvedWidth } = calcEllipsis(leftOffset, text)
+
+          text = subset + _blockEllipsis
           skippedLine = line
           decorationLines[line][1] = resolvedWidth
           isLastDisplayedBeforeEllipsis = true
+        } else if (nextLayout && nextLayout.line !== line) {
+          if (textAlign === 'center') {
+            const { subset, resolvedWidth } = calcEllipsis(leftOffset, text)
+
+            text = subset + _blockEllipsis
+            skippedLine = line
+            decorationLines[line][1] = resolvedWidth
+            isLastDisplayedBeforeEllipsis = true
+          } else {
+            const nextLineText = texts[i + 1]
+
+            const { subset, resolvedWidth } = calcEllipsis(
+              width + leftOffset,
+              nextLineText
+            )
+
+            text = text + subset + _blockEllipsis
+            skippedLine = line
+            decorationLines[line][1] = resolvedWidth
+            isLastDisplayedBeforeEllipsis = true
+          }
         }
       }
     }
@@ -585,9 +638,9 @@ export default async function* buildTextNodes(
         !text.includes(Tab) &&
         !wordSeparators.includes(text) &&
         texts[i + 1] &&
-        wordPositionInLayout[i + 1] &&
-        !wordPositionInLayout[i + 1].isImage &&
-        topOffset === wordPositionInLayout[i + 1].y &&
+        nextLayout &&
+        !nextLayout.isImage &&
+        topOffset === nextLayout.y &&
         !isLastDisplayedBeforeEllipsis
       ) {
         if (wordBuffer === null) {
@@ -648,7 +701,7 @@ export default async function* buildTextNodes(
     // Get the decoration shape.
     if (parentStyle.textDecorationLine) {
       // If it's the last word in the current line.
-      if (line !== wordPositionInLayout[i + 1]?.line || skippedLine === line) {
+      if (line !== nextLayout?.line || skippedLine === line) {
         const deco = decorationLines[line]
         if (deco && !deco[2]) {
           decorationShape += buildDecoration(
@@ -692,6 +745,10 @@ export default async function* buildTextNodes(
       backgroundClipDef += shape
       decorationShape = ''
     }
+
+    if (isLastDisplayedBeforeEllipsis) {
+      break
+    }
   }
 
   // Embed the font as path.
@@ -764,6 +821,44 @@ function processTextTransform(
   return content
 }
 
+function processTextOverflow(
+  parentStyle: Record<string, string | number>,
+  allowSoftWrap: boolean
+): [number, string?] {
+  const {
+    textOverflow,
+    lineClamp,
+    WebkitLineClamp,
+    WebkitBoxOrient,
+    overflow,
+    display,
+  } = parentStyle
+
+  if (display === 'block' && lineClamp) {
+    const [lineLimit, blockEllipsis = HorizontalEllipsis] =
+      parseLineClamp(lineClamp)
+    if (lineLimit) {
+      return [lineLimit, blockEllipsis]
+    }
+  }
+
+  if (
+    textOverflow === 'ellipsis' &&
+    display === '-webkit-box' &&
+    WebkitBoxOrient === 'vertical' &&
+    isNumber(WebkitLineClamp) &&
+    WebkitLineClamp > 0
+  ) {
+    return [WebkitLineClamp, HorizontalEllipsis]
+  }
+
+  if (textOverflow === 'ellipsis' && overflow === 'hidden' && !allowSoftWrap) {
+    return [1, HorizontalEllipsis]
+  }
+
+  return [Infinity]
+}
+
 function processWordBreak(content, wordBreak: string) {
   const allowBreakWord = ['break-all', 'break-word'].includes(wordBreak)
 
@@ -863,3 +958,26 @@ function detectTabs(text: string):
         tabCount: 0,
       }
 }
+
+function parseLineClamp(input: number | string): [number?, string?] {
+  if (typeof input === 'number') return [input]
+
+  const regex1 = /^(\d+)\s*"(.*)"$/
+  const regex2 = /^(\d+)\s*'(.*)'$/
+  const match1 = regex1.exec(input)
+  const match2 = regex2.exec(input)
+
+  if (match1) {
+    const number = +match1[1]
+    const text = match1[2]
+
+    return [number, text]
+  } else if (match2) {
+    const number = +match2[1]
+    const text = match2[2]
+
+    return [number, text]
+  }
+
+  return []
+}

src/utils.ts

@@ -266,6 +266,10 @@ export function isString(x: unknown): x is string {
   return typeof x === 'string'
 }
 
+export function isNumber(x: unknown): x is number {
+  return typeof x === 'number'
+}
+
 export function isUndefined(x: unknown): x is undefined {
   return toString(x) === '[object Undefined]'
 }

test/error.test.tsx

@@ -40,7 +40,7 @@ describe('Error', () => {
       }
     )
     expect(result).rejects.toThrowError(
-      `Invalid value for CSS property "display". Allowed values: "flex" | "none". Received: "inline-block".`
+      `Invalid value for CSS property "display". Allowed values: "flex" | "block" | "none" | "-webkit-box". Received: "inline-block".`
     )
   })