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Add Unicode-aware line wrapping with conservative number protection #53

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Merged
merged 1 commit into from
Nov 4, 2025
Merged

Add Unicode-aware line wrapping with conservative number protection #53

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11 changes: 10 additions & 1 deletion Sources/SwiftMath/MathRender/MTMathUILabel.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -216,6 +216,7 @@ public class MTMathUILabel : MTView {
self.layer?.isGeometryFlipped = true
#else
self.layer.isGeometryFlipped = true
self.clipsToBounds = true
#endif
_fontSize = 20
_contentInsets = MTEdgeInsetsZero
Expand Down Expand Up @@ -305,8 +306,16 @@ public class MTMathUILabel : MTView {
return CGSize(width: -1, height: -1)
}

let resultWidth = displayList!.width + contentInsets.left + contentInsets.right
var resultWidth = displayList!.width + contentInsets.left + contentInsets.right
let resultHeight = displayList!.ascent + displayList!.descent + contentInsets.top + contentInsets.bottom

// Ensure we don't exceed the width constraints
if _preferredMaxLayoutWidth > 0 && resultWidth > _preferredMaxLayoutWidth {
resultWidth = _preferredMaxLayoutWidth
} else if _preferredMaxLayoutWidth == 0 && size.width > 0 && resultWidth > size.width {
resultWidth = size.width
}

return CGSize(width: resultWidth, height: resultHeight)
}

Expand Down
235 changes: 199 additions & 36 deletions Sources/SwiftMath/MathRender/MTTypesetter.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -812,37 +812,67 @@ class MTTypesetter {
// Line is too wide - need to find a break point
let currentText = currentLine.string

// Look for the last space before the current position
if let lastSpaceIndex = currentText.lastIndex(of: " ") {
// Split the line at the last space
let spaceOffset = currentText.distance(from: currentText.startIndex, to: lastSpaceIndex)
// Use Unicode-aware line breaking with number protection
if let breakIndex = findBestBreakPoint(in: currentText, font: styleFont.ctFont, maxWidth: maxWidth) {
// Split the line at the suggested break point
let breakOffset = currentText.distance(from: currentText.startIndex, to: breakIndex)

// Create attributed string for the first line (before space)
let firstLine = NSMutableAttributedString(string: String(currentText.prefix(spaceOffset)))
// Create attributed string for the first line
let firstLine = NSMutableAttributedString(string: String(currentText.prefix(breakOffset)))
firstLine.addAttribute(kCTFontAttributeName as NSAttributedString.Key, value:styleFont.ctFont as Any, range:NSMakeRange(0, firstLine.length))

// Keep track of atoms that belong to the first line
// For simplicity, we'll split atoms at the boundary (this is approximate)
let firstLineAtoms = currentAtoms

// Flush the first line
currentLine = firstLine
currentAtoms = firstLineAtoms
self.addDisplayLine()

// Move down for new line and reset x position
currentPosition.y -= styleFont.fontSize * 1.5
currentPosition.x = 0

// Start the new line with the content after the space
let remainingText = String(currentText.suffix(from: currentText.index(after: lastSpaceIndex)))
currentLine = NSMutableAttributedString(string: remainingText)

// Reset atom list for new line
currentAtoms = []
currentLineIndexRange = NSMakeRange(NSNotFound, NSNotFound)
// Check if first line still exceeds maxWidth - need to find earlier break point
let firstLineCT = CTLineCreateWithAttributedString(firstLine)
let firstLineWidth = CGFloat(CTLineGetTypographicBounds(firstLineCT, nil, nil, nil))

if firstLineWidth > maxWidth {
// Need to break earlier - find previous break point
let firstLineText = firstLine.string
if let earlierBreakIndex = findBestBreakPoint(in: firstLineText, font: styleFont.ctFont, maxWidth: maxWidth) {
let earlierOffset = firstLineText.distance(from: firstLineText.startIndex, to: earlierBreakIndex)
let earlierLine = NSMutableAttributedString(string: String(firstLineText.prefix(earlierOffset)))
earlierLine.addAttribute(kCTFontAttributeName as NSAttributedString.Key, value:styleFont.ctFont as Any, range:NSMakeRange(0, earlierLine.length))

// Flush the earlier line
currentLine = earlierLine
currentAtoms = [] // Approximate - we're splitting
self.addDisplayLine()

// Move down for new line
currentPosition.y -= styleFont.fontSize * 1.5
currentPosition.x = 0

// Remaining text includes everything after the earlier break
let remainingText = String(firstLineText.suffix(from: earlierBreakIndex)) +
String(currentText.suffix(from: breakIndex))
currentLine = NSMutableAttributedString(string: remainingText)
currentAtoms = []
currentLineIndexRange = NSMakeRange(NSNotFound, NSNotFound)
}
} else {
// First line fits - proceed with normal wrapping
// Keep track of atoms that belong to the first line
let firstLineAtoms = currentAtoms

// Flush the first line
currentLine = firstLine
currentAtoms = firstLineAtoms
self.addDisplayLine()

// Move down for new line and reset x position
currentPosition.y -= styleFont.fontSize * 1.5
currentPosition.x = 0

// Start the new line with the content after the break
let remainingText = String(currentText.suffix(from: breakIndex))
currentLine = NSMutableAttributedString(string: remainingText)

// Reset atom list for new line
currentAtoms = []
currentLineIndexRange = NSMakeRange(NSNotFound, NSNotFound)
}
}
// If no space found, let it overflow (better than breaking mid-word)
// If no break point found, let it overflow (better than breaking mid-word)
}
}
// add the atom to the current range
Expand Down Expand Up @@ -890,7 +920,109 @@ class MTTypesetter {
display?.width += interElementSpace
}
}


// MARK: - Unicode-aware Line Breaking

/// Find the best break point using Core Text, with conservative number protection
func findBestBreakPoint(in text: String, font: CTFont, maxWidth: CGFloat) -> String.Index? {
let attributes: [NSAttributedString.Key: Any] = [kCTFontAttributeName as NSAttributedString.Key: font]
let attrString = NSAttributedString(string: text, attributes: attributes)
let typesetter = CTTypesetterCreateWithAttributedString(attrString as CFAttributedString)
let suggestedBreak = CTTypesetterSuggestLineBreak(typesetter, 0, Double(maxWidth))

guard suggestedBreak > 0 && suggestedBreak < text.count else {
return nil
}

let breakIndex = text.index(text.startIndex, offsetBy: suggestedBreak)

// Conservative check: verify we're not breaking within a number
if isBreakingSafeForNumbers(text: text, breakIndex: breakIndex) {
return breakIndex
}

// If the suggested break would split a number, find the previous safe break point
return findPreviousSafeBreak(in: text, before: breakIndex)
}

/// Check if breaking at this index would split a number
func isBreakingSafeForNumbers(text: String, breakIndex: String.Index) -> Bool {
guard breakIndex > text.startIndex && breakIndex < text.endIndex else {
return true
}

// Check a small window around the break point
let beforeIndex = text.index(before: breakIndex)
let charBefore = text[beforeIndex]
let charAfter = text[breakIndex]

// Number separators in various locales
let numberSeparators: Set<Character> = [
".", ",", // Decimal/thousands (EN/FR)
"'", // Thousands (CH)
"\u{00A0}", // Non-breaking space (FR thousands)
"\u{2009}", // Thin space (sometimes used)
"\u{202F}" // Narrow no-break space (FR)
]

// Pattern 1: digit + separator + digit (e.g., "3.14" or "3,14")
if charBefore.isNumber && numberSeparators.contains(charAfter) {
// Check if there's a digit after the separator
let nextIndex = text.index(after: breakIndex)
if nextIndex < text.endIndex && text[nextIndex].isNumber {
return false // Don't break: this looks like "3.|14"
}
}

// Pattern 2: separator + digit, check if previous is digit
if numberSeparators.contains(charBefore) && charAfter.isNumber {
// Check if there's a digit before the separator
if beforeIndex > text.startIndex {
let prevIndex = text.index(before: beforeIndex)
if text[prevIndex].isNumber {
return false // Don't break: this looks like "3,|14"
}
}
}

// Pattern 3: digit + digit (shouldn't happen with CTTypesetter, but be safe)
if charBefore.isNumber && charAfter.isNumber {
return false // Don't break within consecutive digits
}

// Pattern 4: digit + space + digit (French: "1 000 000")
if charBefore.isNumber && charAfter.isWhitespace {
let nextIndex = text.index(after: breakIndex)
if nextIndex < text.endIndex && text[nextIndex].isNumber {
return false // Don't break: this looks like "1 |000"
}
}

return true // Safe to break
}

/// Find previous safe break point before the given index
func findPreviousSafeBreak(in text: String, before breakIndex: String.Index) -> String.Index? {
var currentIndex = breakIndex

// Walk backwards to find a space or safe break
while currentIndex > text.startIndex {
currentIndex = text.index(before: currentIndex)

// Prefer breaking at whitespace (safest option)
if text[currentIndex].isWhitespace {
return text.index(after: currentIndex) // Break after the space
}

// Check if this would be safe
if isBreakingSafeForNumbers(text: text, breakIndex: currentIndex) {
return currentIndex
}
}

return nil
}

/// Check if the current line exceeds maxWidth and break if needed
func checkAndBreakLine() {
guard maxWidth > 0 && currentLine.length > 0 else { return }
Expand All @@ -906,15 +1038,46 @@ class MTTypesetter {
// Line is too wide - need to find a break point
let currentText = currentLine.string

// Look for the last space before the current position
if let lastSpaceIndex = currentText.lastIndex(of: " ") {
// Split the line at the last space
let spaceOffset = currentText.distance(from: currentText.startIndex, to: lastSpaceIndex)
// Use Unicode-aware line breaking with number protection
if let breakIndex = findBestBreakPoint(in: currentText, font: styleFont.ctFont, maxWidth: maxWidth) {
// Split the line at the suggested break point
let breakOffset = currentText.distance(from: currentText.startIndex, to: breakIndex)

// Create attributed string for the first line (before space)
let firstLine = NSMutableAttributedString(string: String(currentText.prefix(spaceOffset)))
// Create attributed string for the first line
let firstLine = NSMutableAttributedString(string: String(currentText.prefix(breakOffset)))
firstLine.addAttribute(kCTFontAttributeName as NSAttributedString.Key, value:styleFont.ctFont as Any, range:NSMakeRange(0, firstLine.length))

// Check if first line still exceeds maxWidth - need to find earlier break point
let firstLineCT = CTLineCreateWithAttributedString(firstLine)
let firstLineWidth = CGFloat(CTLineGetTypographicBounds(firstLineCT, nil, nil, nil))

if firstLineWidth > maxWidth {
// Need to break earlier - find previous break point
let firstLineText = firstLine.string
if let earlierBreakIndex = findBestBreakPoint(in: firstLineText, font: styleFont.ctFont, maxWidth: maxWidth) {
let earlierOffset = firstLineText.distance(from: firstLineText.startIndex, to: earlierBreakIndex)
let earlierLine = NSMutableAttributedString(string: String(firstLineText.prefix(earlierOffset)))
earlierLine.addAttribute(kCTFontAttributeName as NSAttributedString.Key, value:styleFont.ctFont as Any, range:NSMakeRange(0, earlierLine.length))

// Flush the earlier line
currentLine = earlierLine
currentAtoms = []
self.addDisplayLine()

// Move down for new line
currentPosition.y -= styleFont.fontSize * 1.5
currentPosition.x = 0

// Remaining text includes everything after the earlier break
let remainingText = String(firstLineText.suffix(from: earlierBreakIndex)) +
String(currentText.suffix(from: breakIndex))
currentLine = NSMutableAttributedString(string: remainingText)
currentAtoms = []
currentLineIndexRange = NSMakeRange(NSNotFound, NSNotFound)
return
}
}

// Keep track of atoms that belong to the first line
let firstLineAtoms = currentAtoms

Expand All @@ -927,8 +1090,8 @@ class MTTypesetter {
currentPosition.y -= styleFont.fontSize * 1.5
currentPosition.x = 0

// Start the new line with the content after the space
let remainingText = String(currentText.suffix(from: currentText.index(after: lastSpaceIndex)))
// Start the new line with the content after the break
let remainingText = String(currentText.suffix(from: breakIndex))
currentLine = NSMutableAttributedString(string: remainingText)

// Reset atom list for new line
Expand Down
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