Improve performance of layoutMultilineText Hopding#1203 / seibar

src/api/text/layout.ts

@@ -137,16 +137,61 @@ const splitOutLines = (
   font: PDFFont,
   fontSize: number,
 ) => {
-  let lastWhitespaceIdx = input.length;
-  while (lastWhitespaceIdx > 0) {
-    const line = input.substring(0, lastWhitespaceIdx);
-    const encoded = font.encodeText(line);
-    const width = font.widthOfTextAtSize(line, fontSize);
-    if (width < maxWidth) {
-      const remainder = input.substring(lastWhitespaceIdx) || undefined;
-      return { line, encoded, width, remainder };
+  if (font.widthOfTextAtSize(input, fontSize) > maxWidth) {
+     const tokens: string[] = [''];
+     const whitespaces: string[] = [];
+     let width = 0;
+
+     for (let i = 0; i < input.length; i++) {
+       const s = input[i];
+
+       // If this character puts us over then we're done.
+       if (width + font.widthOfTextAtSize(s, fontSize) >= maxWidth) {
+         let line = '';
+         let remainder;
+         if (/\s/.test(s)) {
+           line = tokens
+             .map((token, tokenIdx) => token + (whitespaces[tokenIdx] ?? ''))
+             .join('');
+           remainder = input.substring(i) || undefined;
+         } else {
+           // We're in the middle of a token so go back to the last token and
+           // adjust remainder based on the length of the current incomplete token
+           line = tokens
+             .slice(0, tokens.length - 1)
+             .map((token, tokenIdx) => token + (whitespaces[tokenIdx] ?? ''))
+             .join('');
+
+           const whitespaceLength = (whitespaces[whitespaces.length - 1] || '')
+             .length;
+           const tokenLength = (tokens[tokens.length - 1] || '').length;
+           if (whitespaceLength === 0) {
+             // Not able to layout this input within the maxWidth.
+             break;
+           }
+           const remainderIndex = i - whitespaceLength - tokenLength;
+           remainder = input.substring(remainderIndex) || undefined;
+         }
+
+         return {
+           line,
+           encoded: font.encodeText(line),
+           width: font.widthOfTextAtSize(line, fontSize),
+           remainder,
+         };
+       }
+
+       if (/\s/.test(s)) {
+         // Found a word boundary.
+         // We will add each subsequent character to the current token until we find another word boundary.
+         whitespaces.push(s);
+         tokens.push('');
+       } else {
+         tokens[tokens.length - 1] += s;
+       }
+
+       width += font.widthOfTextAtSize(s, fontSize);
     }
-    lastWhitespaceIdx = lastIndexOfWhitespace(line) ?? 0;
   }
 
   // We were unable to split the input enough to get a chunk that would fit