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Merge pull request #445 from SixLabors/js/additional-linebreak-fixes
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Fix Linebreak issues #443 and #444
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@JimBobSquarePants
JimBobSquarePants authored Jan 29, 2025
2 parents a82862f + 23fda1d commit b98614c
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Showing 12 changed files with 265 additions and 141 deletions.
257 changes: 116 additions & 141 deletions src/SixLabors.Fonts/TextLayout.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
// Licensed under the Six Labors Split License.

using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Numerics;
using SixLabors.Fonts.Tables.AdvancedTypographic;
using SixLabors.Fonts.Unicode;
Expand Down Expand Up @@ -1181,149 +1182,117 @@ VerticalOrientationType.Rotate or
lineBreaks.Add(lineBreakEnumerator.Current);
}

// Then split the line at the line breaks.
int lineBreakIndex = 0;
int maxLineBreakIndex = lineBreaks.Count - 1;
LineBreak lastLineBreak = lineBreaks[lineBreakIndex];
LineBreak currentLineBreak = lineBreaks[lineBreakIndex];
float lineAdvance = 0;

for (int i = 0; i < textLine.Count; i++)
int usedOffset = 0;
while (textLine.Count > 0)
{
int max = textLine.Count - 1;
TextLine.GlyphLayoutData glyph = textLine[i];
codePointIndex = glyph.CodePointIndex;
int graphemeCodePointIndex = glyph.GraphemeCodePointIndex;

if (graphemeCodePointIndex == 0 && textLine.Count > 0)
LineBreak? bestBreak = null;
foreach (LineBreak lineBreak in lineBreaks)
{
lineAdvance += glyph.ScaledAdvance;
// Adjust the break index relative to the current position in the original line
int measureAt = lineBreak.PositionMeasure - usedOffset;

// Skip breaks that are already behind the trimmed portion
if (measureAt < 0)
{
continue;
}

if (codePointIndex == currentLineBreak.PositionWrap && currentLineBreak.Required)
// Measure the text up to the adjusted break point
float measure = textLine.MeasureAt(measureAt);
if (measure > wrappingLength)
{
// Mandatory line break at index.
TextLine remaining = textLine.SplitAt(i);
// Stop and use the best break so far
bestBreak ??= lineBreak;
break;
}

// Update the best break
bestBreak = lineBreak;

if (shouldWrap && textLine.ScaledLineAdvance - glyph.ScaledAdvance > wrappingLength)
// If it's a mandatory break, stop immediately
if (lineBreak.Required)
{
break;
}
}

if (bestBreak != null)
{
if (breakAll)
{
// Break-all works differently to the other modes.
// It will break at any character so we simply toggle the breaking operation depending
// on whether the break is required.
TextLine? remaining;
if (bestBreak.Value.Required)
{
// We've overshot the wrapping length so we need to split the line
// at the previous break and add both lines.
TextLine overflow = textLine.SplitAt(lastLineBreak, keepAll);
if (overflow != textLine)
if (textLine.TrySplitAt(bestBreak.Value, keepAll, out remaining))
{
usedOffset += textLine.Count;
textLines.Add(textLine.Finalize(options));
textLine = overflow;
textLine = remaining;
}

}
else if (textLine.TrySplitAt(wrappingLength, out remaining))
{
usedOffset += textLine.Count;
textLines.Add(textLine.Finalize(options));
textLine = remaining;
i = -1;
lineAdvance = 0;
}
else
{
textLines.Add(textLine.Finalize(options));
textLine = remaining;
i = -1;
lineAdvance = 0;
usedOffset += textLine.Count;
}
}
else if (shouldWrap)
else
{
if (lineAdvance >= wrappingLength)
// Split the current line at the adjusted break index
if (textLine.TrySplitAt(bestBreak.Value, keepAll, out TextLine? remaining))
{
if (breakAll)
usedOffset += textLine.Count;
if (breakWord)
{
// Insert a forced break.
TextLine remaining = textLine.SplitAt(i);
if (remaining != textLine)
// A break was found, but we need to check if the line is too long
// and break if required.
if (textLine.ScaledLineAdvance > wrappingLength &&
textLine.TrySplitAt(wrappingLength, out TextLine? overflow))
{
textLines.Add(textLine.Finalize(options));
textLine = remaining;
i = -1;
lineAdvance = 0;
// Reinsert the overflow at the beginning of the remaining line
usedOffset -= overflow.Count;
remaining.InsertAt(0, overflow);
}
}
else if (codePointIndex == currentLineBreak.PositionWrap || i == max)
{
LineBreak lineBreak = lineAdvance == wrappingLength
? currentLineBreak
: lastLineBreak;

if (i > 0)
{
// If the current break is a space, and the line minus the space
// is less than the wrapping length, we can break using the current break.
float previousAdvance = lineAdvance - glyph.ScaledAdvance;
TextLine.GlyphLayoutData lastGlyph = textLine[i - 1];
if (CodePoint.IsWhiteSpace(lastGlyph.CodePoint))
{
previousAdvance -= lastGlyph.ScaledAdvance;
if (previousAdvance <= wrappingLength)
{
lineBreak = currentLineBreak;
}
}
}

// If we are at the position wrap we can break here.
// Split the line at the appropriate break.
// CJK characters will not be split if 'keepAll' is true.
TextLine remaining = textLine.SplitAt(lineBreak, keepAll);

if (remaining != textLine)
{
if (breakWord)
{
// If the line is too long, insert a forced break.
if (textLine.ScaledLineAdvance > wrappingLength)
{
TextLine overflow = textLine.SplitAt(wrappingLength);
if (overflow != textLine)
{
remaining.InsertAt(0, overflow);
}
}
}

textLines.Add(textLine.Finalize(options));
textLine = remaining;
i = -1;
lineAdvance = 0;
}
}
// Add the split part to the list and continue processing.
textLines.Add(textLine.Finalize(options));
textLine = remaining;
}
else
{
usedOffset += textLine.Count;
}
}
}

// Find the next line break.
if (lineBreakIndex < maxLineBreakIndex &&
(currentLineBreak.PositionWrap == codePointIndex))
{
lastLineBreak = currentLineBreak;
currentLineBreak = lineBreaks[++lineBreakIndex];
}
}

// Add the final line.
if (textLine.Count > 0)
{
if (shouldWrap && (breakWord || breakAll))
else
{
while (textLine.ScaledLineAdvance > wrappingLength)
// If no valid break is found, add the remaining line and exit
if (breakWord || breakAll)
{
TextLine overflow = textLine.SplitAt(wrappingLength);
if (overflow == textLine)
while (textLine.ScaledLineAdvance > wrappingLength)
{
break;
}
if (!textLine.TrySplitAt(wrappingLength, out TextLine? overflow))
{
break;
}

textLines.Add(textLine.Finalize(options));
textLine = overflow;
textLines.Add(textLine.Finalize(options));
textLine = overflow;
}
}
}

textLines.Add(textLine.Finalize(options));
textLines.Add(textLine.Finalize(options));
break;
}
}

return new TextBox(textLines);
Expand Down Expand Up @@ -1381,7 +1350,7 @@ public void Add(
{
// Reset metrics.
// We track the maximum metrics for each line to ensure glyphs can be aligned.
if (graphemeIndex == 0)
if (graphemeCodePointIndex == 0)
{
this.ScaledLineAdvance += scaledAdvance;
}
Expand All @@ -1406,31 +1375,36 @@ public void Add(
stringIndex));
}

public TextLine InsertAt(int index, TextLine textLine)
public void InsertAt(int index, TextLine textLine)
{
this.data.InsertRange(index, textLine.data);
RecalculateLineMetrics(this);
return this;
}

public TextLine SplitAt(int index)
public float MeasureAt(int index)
{
if (index == 0 || index >= this.Count)
if (index >= this.data.Count)
{
return this;
index = this.data.Count - 1;
}

int count = this.data.Count - index;
TextLine result = new(count);
result.data.AddRange(this.data.GetRange(index, count));
RecalculateLineMetrics(result);
while (index >= 0 && CodePoint.IsWhiteSpace(this.data[index].CodePoint))
{
// If the index is whitespace, we need to measure at the previous
// non-whitespace glyph to ensure we don't break too early.
index--;
}

this.data.RemoveRange(index, count);
RecalculateLineMetrics(this);
return result;
float advance = 0;
for (int i = 0; i <= index; i++)
{
advance += this.data[i].ScaledAdvance;
}

return advance;
}

public TextLine SplitAt(float length)
public bool TrySplitAt(float length, [NotNullWhen(true)] out TextLine? result)
{
float advance = this.data[0].ScaledAdvance;

Expand All @@ -1449,20 +1423,21 @@ public TextLine SplitAt(float length)
if (advance >= length)
{
int count = this.data.Count - i;
TextLine result = new(count);
result = new(count);
result.data.AddRange(this.data.GetRange(i, count));
RecalculateLineMetrics(result);

this.data.RemoveRange(i, count);
RecalculateLineMetrics(this);
return result;
return true;
}
}

return this;
result = null;
return false;
}

public TextLine SplitAt(LineBreak lineBreak, bool keepAll)
public bool TrySplitAt(LineBreak lineBreak, bool keepAll, [NotNullWhen(true)] out TextLine? result)
{
int index = this.data.Count;
GlyphLayoutData glyphWrap = default;
Expand All @@ -1475,14 +1450,12 @@ public TextLine SplitAt(LineBreak lineBreak, bool keepAll)
}
}

if (index == 0)
{
return this;
}

// Word breaks should not be used for Chinese/Japanese/Korean (CJK) text
// when word-breaking mode is keep-all.
if (!lineBreak.Required && keepAll && UnicodeUtility.IsCJKCodePoint((uint)glyphWrap.CodePoint.Value))
if (index > 0
&& !lineBreak.Required
&& keepAll
&& UnicodeUtility.IsCJKCodePoint((uint)glyphWrap.CodePoint.Value))
{
// Loop through previous glyphs to see if there is
// a non CJK codepoint we can break at.
Expand All @@ -1495,23 +1468,25 @@ public TextLine SplitAt(LineBreak lineBreak, bool keepAll)
break;
}
}
}

if (index == 0)
{
return this;
}
if (index == 0)
{
result = null;
return false;
}

// Create a new line ensuring we capture the initial metrics.
int count = this.data.Count - index;
TextLine result = new(count);
result = new(count);
result.data.AddRange(this.data.GetRange(index, count));
RecalculateLineMetrics(result);

// Remove those items from this line.
this.data.RemoveRange(index, count);
RecalculateLineMetrics(this);
return result;

return true;
}

private void TrimTrailingWhitespace()
Expand Down
3 changes: 3 additions & 0 deletions tests/Images/ReferenceOutput/Issue_444_A__WrappingLength_860_.png
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3 changes: 3 additions & 0 deletions tests/Images/ReferenceOutput/Issue_444_B__WrappingLength_860_.png
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3 changes: 3 additions & 0 deletions tests/Images/ReferenceOutput/Issue_444_C__WrappingLength_860_.png
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3 changes: 3 additions & 0 deletions tests/Images/ReferenceOutput/Issue_444_D__WrappingLength_860_.png
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3 changes: 3 additions & 0 deletions tests/Images/ReferenceOutput/Issue_444_E__WrappingLength_860_.png
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3 changes: 3 additions & 0 deletions tests/Images/ReferenceOutput/ShouldBreakIntoTwoLinesA__WrappingLength_1000_.png
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