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Fix line width calculation for expressions with superscripts/subscripts

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The typesetter was incorrectly measuring line width when expressions contained
  superscripts or subscripts (e.g., b²). After rendering a superscript, the line
  is split into multiple display segments, but the width checking code was only
  measuring the current segment, not the total visual line width.

  Key changes:
  - Use currentPosition.x to track actual horizontal position across all segments
  - Calculate visualLineWidth = currentPosition.x + currentSegmentWidth
  - Pass remainingWidth (maxWidth - currentPosition.x) to findBestBreakPoint
  - Apply fix to both interatom breaking and inline text breaking

  This fixes truncation issues where content like "Δ=b²-4ac avec a=1..." was
  being clipped instead of wrapped to a new line.

  Before: Each segment checked in isolation → segments appeared to fit individually
          but total visual width exceeded maxWidth → content truncated/clipped

  After:  Total visual width tracked correctly → line breaking triggered when
          actual visual width exceeds maxWidth → content wraps properly
This commit is contained in:
Nicolas Guillot
2025-11-17 17:51:30 +01:00
parent 43c69240bd
commit 3aa6c6c98b
3 changed files with 57 additions and 23 deletions
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15
Sources/SwiftMath/MathRender/MTMathUILabel.swift
View File

@@ -278,24 +278,9 @@ public class MTMathUILabel : MTView {
let effectiveWidth = _preferredMaxLayoutWidth > 0 ? _preferredMaxLayoutWidth : bounds.size.width
let availableWidth = effectiveWidth - contentInsets.left - contentInsets.right
print("🔧 MTMathUILabel _layoutSubviews:")
print(" preferredMaxLayoutWidth: \(_preferredMaxLayoutWidth)")
print(" bounds.size.width: \(bounds.size.width)")
print(" effectiveWidth: \(effectiveWidth)")
print(" availableWidth: \(availableWidth)")
print(" LaTeX: \(_latex.prefix(60))...")
// print("Pre list = \(_mathList!)")
_displayList = MTTypesetter.createLineForMathList(_mathList, font: self.font, style: currentStyle, maxWidth: availableWidth)
_displayList!.textColor = textColor
print(" Display subDisplays count: \(_displayList!.subDisplays.count)")
for (index, subDisplay) in _displayList!.subDisplays.enumerated() {
print(" Display \(index): type=\(type(of: subDisplay)), x=\(subDisplay.position.x), width=\(subDisplay.width)")
if let lineDisplay = subDisplay as? MTCTLineDisplay {
print(" Content: '\(lineDisplay.attributedString?.string ?? "")'")
}
}
// print("Post list = \(_mathList!)")
var textX = CGFloat(0)
switch self.textAlignment {

32
Sources/SwiftMath/MathRender/MTTypesetter.swift
View File

@@ -557,7 +557,10 @@ class MTTypesetter {
// starts with a letter, they're part of the same word - don't break!
// Example: "...é" + "quivaut" should not break
// But "...km " + "équivaut" can break (has space)
if lastChar.isLetter && firstChar.isLetter {
// IMPORTANT: Only apply this to multi-character atoms (text words), not single
// letters (math variables). In math "4ac" splits as "4","a","c" - these are
// separate and CAN be broken between.
if lastChar.isLetter && firstChar.isLetter && atom.nucleus.count > 1 {
// Don't break - this would split a word
return false
}
@@ -565,9 +568,14 @@ class MTTypesetter {
}
// Calculate what the width would be if we add this atom
// IMPORTANT: Use currentPosition.x instead of getCurrentLineWidth()
// because currentLine only measures the current text segment, but after
// superscripts/subscripts, the line may be split into multiple segments.
// currentPosition.x tracks the actual visual horizontal position.
let currentLineWidth = getCurrentLineWidth()
let visualLineWidth = currentPosition.x + currentLineWidth
let atomWidth = calculateAtomWidth(atom, prevNode: prevNode)
let projectedWidth = currentLineWidth + atomWidth
let projectedWidth = visualLineWidth + atomWidth
// If we're well within the limit, no need to break
if projectedWidth <= maxWidth {
@@ -1213,14 +1221,22 @@ class MTTypesetter {
let attrString = currentLine.mutableCopy() as! NSMutableAttributedString
attrString.addAttribute(kCTFontAttributeName as NSAttributedString.Key, value:styleFont.ctFont as Any, range:NSMakeRange(0, attrString.length))
let ctLine = CTLineCreateWithAttributedString(attrString)
let lineWidth = CGFloat(CTLineGetTypographicBounds(ctLine, nil, nil, nil))
let segmentWidth = CGFloat(CTLineGetTypographicBounds(ctLine, nil, nil, nil))
if lineWidth > maxWidth {
// IMPORTANT: Account for currentPosition.x to get the true visual line width
// After superscripts/subscripts, currentPosition.x > 0 because previous segments
// have been rendered and flushed
let visualLineWidth = currentPosition.x + segmentWidth
if visualLineWidth > maxWidth {
// Line is too wide - need to find a break point
let currentText = currentLine.string
// Use Unicode-aware line breaking with number protection
if let breakIndex = findBestBreakPoint(in: currentText, font: styleFont.ctFont, maxWidth: maxWidth) {
// IMPORTANT: Use remaining width, not full maxWidth, because currentPosition.x
// may be > 0 if we've already rendered segments on this visual line
let remainingWidth = max(0, maxWidth - currentPosition.x)
if let breakIndex = findBestBreakPoint(in: currentText, font: styleFont.ctFont, maxWidth: remainingWidth) {
// Split the line at the suggested break point
let breakOffset = currentText.distance(from: currentText.startIndex, to: breakIndex)
@@ -1228,14 +1244,14 @@ class MTTypesetter {
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
// Check if first line still exceeds remaining width - need to find earlier break point
let firstLineCT = CTLineCreateWithAttributedString(firstLine)
let firstLineWidth = CGFloat(CTLineGetTypographicBounds(firstLineCT, nil, nil, nil))
if firstLineWidth > maxWidth {
if firstLineWidth > remainingWidth {
// Need to break earlier - find previous break point
let firstLineText = firstLine.string
if let earlierBreakIndex = findBestBreakPoint(in: firstLineText, font: styleFont.ctFont, maxWidth: maxWidth) {
if let earlierBreakIndex = findBestBreakPoint(in: firstLineText, font: styleFont.ctFont, maxWidth: remainingWidth) {
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))