fix: update text encoding to handle surrogate pairs in AFMFont and font substitution

Author: romenmedina-aircury

packages/pdfkit/src/font/afm.js

@@ -206,29 +206,28 @@ class AFMFont {
 
   encodeText(text) {
     const res = [];
-    for (
-      let i = 0, end = text.length, asc = 0 <= end;
-      asc ? i < end : i > end;
-      asc ? i++ : i--
-    ) {
-      let char = text.charCodeAt(i);
-      char = WIN_ANSI_MAP[char] || char;
+    let i = 0;
+    
+    while (i < text.length) {
+      const codePoint = text.codePointAt(i);
+      const char = WIN_ANSI_MAP[codePoint] || codePoint;
       res.push(char.toString(16));
+      
+      i += codePoint > 0xFFFF ? 2 : 1;
     }
 
     return res;
   }
 
   glyphsForString(string) {
     const glyphs = [];
+    let i = 0;
+    
+    while (i < string.length) {
+      const codePoint = string.codePointAt(i);
+      glyphs.push(this.characterToGlyph(codePoint));
 
-    for (
-      let i = 0, end = string.length, asc = 0 <= end;
-      asc ? i < end : i > end;
-      asc ? i++ : i--
-    ) {
-      const charCode = string.charCodeAt(i);
-      glyphs.push(this.characterToGlyph(charCode));
+      i += codePoint > 0xFFFF ? 2 : 1;
     }
 
     return glyphs;

packages/textkit/src/engines/fontSubstitution/index.ts

@@ -49,9 +49,9 @@ const fontSubstitution =
 
       const chars = string.slice(run.start, run.end);
 
-      for (let j = 0; j < chars.length; j += 1) {
-        const char = chars[j];
-        const codePoint = char.codePointAt(0);
+      let j = 0;
+      while (j < chars.length) {
+        const codePoint = chars.codePointAt(j);
         // If the default font does not have a glyph and the fallback font does, we use it
         const font = pickFontFromFontStack(
           codePoint,
@@ -83,7 +83,10 @@ const fontSubstitution =
           lastIndex = index;
         }
 
-        index += char.length;
+        // Calculate character length based on code point (1 for BMP, 2 for others)
+        const charLength = codePoint > 0xffff ? 2 : 1;
+        j += charLength;
+        index += charLength;
       }
     }