add a fallback font system to render CJK text in the \text command

Sources/SwiftMath/MathRender/MTFont.swift

@@ -11,12 +11,18 @@ import CoreText
 //
 
 public class MTFont {
-    
+
     var defaultCGFont: CGFont!
     var ctFont: CTFont!
     var mathTable: MTFontMathTable?
     var rawMathTable: NSDictionary?
-    
+
+    /// Fallback font for characters not supported by the main math font.
+    /// Defaults to the system font at the same size. This is particularly useful
+    /// for rendering text in \text{} commands with characters outside the math font's coverage
+    /// (e.g., Chinese, Japanese, Korean, emoji, etc.)
+    public var fallbackFont: CTFont?
+
     init() {}
     
     /// `MTFont(fontWithName:)` does not load the complete math font, it only has about half the glyphs of the full math font.

Sources/SwiftMath/MathRender/MTMathListBuilder.swift

@@ -438,8 +438,15 @@ public struct MTMathListBuilder {
             } else {
                 atom = MTMathAtomFactory.atom(forCharacter: char)
                 if atom == nil {
-                    // Not a recognized character
-                    continue
+                    // Not a recognized character in standard math mode
+                    // In text mode (spacesAllowed && roman style), accept any Unicode character for fallback font support
+                    // This enables Chinese, Japanese, Korean, emoji, etc. in \text{} commands
+                    if spacesAllowed && currentFontStyle == .roman {
+                        atom = MTMathAtom(type: .ordinary, value: String(char))
+                    } else {
+                        // In math mode or non-text commands, skip unrecognized characters
+                        continue
+                    }
                 }
             }
             

Sources/SwiftMath/MathRender/MTTypesetter.swift

@@ -1276,11 +1276,18 @@ class MTTypesetter {
     func findGlyphForCharacterAtIndex(_ index:String.Index, inString str:String) -> CGGlyph {
         // Get the character at index taking into account UTF-32 characters
         var chars = Array(str[index].utf16)
-        
+
         // Get the glyph from the font
         var glyph = [CGGlyph](repeating: CGGlyph.zero, count: chars.count)
         let found = CTFontGetGlyphsForCharacters(styleFont.ctFont, &chars, &glyph, chars.count)
         if !found {
+            // Try fallback font if available
+            if let fallbackFont = styleFont.fallbackFont {
+                let fallbackFound = CTFontGetGlyphsForCharacters(fallbackFont, &chars, &glyph, chars.count)
+                if fallbackFound {
+                    return glyph[0]
+                }
+            }
             // the font did not contain a glyph for our character, so we just return 0 (notdef)
             return 0
         }