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Fixes rounding error while glyphrun serialization #6295

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Merged
merged 1 commit into from
May 10, 2022
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Fixes rounding error while glyphrun serialization #6295

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10 changes: 9 additions & 1 deletion src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/GlyphsSerializer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,8 @@ public GlyphsSerializer(GlyphRun glyphRun)
_advances = glyphRun.AdvanceWidths;
_offsets = glyphRun.GlyphOffsets;

_advanceWidthRoundingError = 0.0;

// "100,50,,0;".Length is a capacity estimate for an individual glyph
_glyphStringBuider = new StringBuilder(10);

Expand All @@ -82,6 +84,8 @@ public GlyphsSerializer(GlyphRun glyphRun)
/// </summary>
public void ComputeContentStrings(out string characters, out string indices, out string caretStops)
{
_advanceWidthRoundingError = 0.0;

if (_clusters != null)
{
// the algorithm works by finding (n:m) clusters and appending m glyphs for each cluster
Expand Down Expand Up @@ -184,7 +188,9 @@ private void AddGlyph(int glyph, int sourceCharacter)
_glyphStringBuider.Append(GlyphSubEntrySeparator);

// advance width
int normalizedAdvance = (int)Math.Round(_advances[glyph] * _milToEm);
double unroundedAdvance = _advances[glyph] * _milToEm;
int normalizedAdvance = (int)Math.Round(unroundedAdvance + _advanceWidthRoundingError);
_advanceWidthRoundingError += (unroundedAdvance - (double)normalizedAdvance);
double fontAdvance = _sideways ? _glyphTypeface.AdvanceHeights[fontIndex] : _glyphTypeface.AdvanceWidths[fontIndex];
if (normalizedAdvance != (int)Math.Round(fontAdvance * EmScaleFactor))
{
Expand Down Expand Up @@ -320,6 +326,8 @@ private string CreateCaretStopsString()

private int _glyphClusterInitialOffset;

private double _advanceWidthRoundingError;

private IList<ushort> _clusters;

private IList<ushort> _indices;
Expand Down