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[release/7.0] GlyphSerializer rounding fix #7721

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Merged
merged 2 commits into from
May 9, 2023
Merged

[release/7.0] GlyphSerializer rounding fix #7721

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1423ba3
GlyphSerializer rounding fix
miloush Feb 16, 2023
dc0a30a
double constants
miloush Feb 18, 2023
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35 changes: 27 additions & 8 deletions 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 @@ -64,7 +64,8 @@ public GlyphsSerializer(GlyphRun glyphRun)
_advances = glyphRun.AdvanceWidths;
_offsets = glyphRun.GlyphOffsets;

_advanceWidthRoundingError = 0.0;
_currentAdvanceTotal = 0.0;
_idealAdvanceTotal = 0.0;

// "100,50,,0;".Length is a capacity estimate for an individual glyph
_glyphStringBuider = new StringBuilder(10);
Expand All @@ -84,7 +85,8 @@ public GlyphsSerializer(GlyphRun glyphRun)
/// </summary>
public void ComputeContentStrings(out string characters, out string indices, out string caretStops)
{
_advanceWidthRoundingError = 0.0;
_currentAdvanceTotal = 0.0;
_idealAdvanceTotal = 0.0;

if (_clusters != null)
{
Expand Down Expand Up @@ -188,13 +190,28 @@ private void AddGlyph(int glyph, int sourceCharacter)
_glyphStringBuider.Append(GlyphSubEntrySeparator);

// advance width
double unroundedAdvance = _advances[glyph] * _milToEm;
int normalizedAdvance = (int)Math.Round(unroundedAdvance + _advanceWidthRoundingError);
_advanceWidthRoundingError += (unroundedAdvance - (double)normalizedAdvance);
// #7499 Advance width needs to be specified if it differs from what is in the font tables. [ECMA-388 O5.5]
// Most commonly it differs after shaping, e.g. when kerning is applied. (Ex. 12-15)
// XPS supports floating point values, but in the interest of file size, we want to specify integers.

double shapingAdvance = _advances[glyph] * _milToEm;
double fontAdvance = _sideways ? _glyphTypeface.AdvanceHeights[fontIndex] : _glyphTypeface.AdvanceWidths[fontIndex];
if (normalizedAdvance != (int)Math.Round(fontAdvance * EmScaleFactor))

// To minimize rounding errors, we keep track of the unrounded advance total as required by [M5.6].
int roundedShapingAdvance = (int)Math.Round(_idealAdvanceTotal + shapingAdvance - _currentAdvanceTotal);
int roundedFontAdvance = (int)Math.Round(fontAdvance);

if (roundedShapingAdvance != roundedFontAdvance)
{
_glyphStringBuider.Append(normalizedAdvance.ToString(CultureInfo.InvariantCulture));
_glyphStringBuider.Append(roundedShapingAdvance.ToString(CultureInfo.InvariantCulture));
_currentAdvanceTotal += roundedShapingAdvance;
_idealAdvanceTotal += shapingAdvance;
}
else
{
// when the value comes from the font tables, the specification does not mandate clients to do any rounding
_currentAdvanceTotal += fontAdvance;
_idealAdvanceTotal += fontAdvance;
}

_glyphStringBuider.Append(GlyphSubEntrySeparator);
Expand Down Expand Up @@ -326,7 +343,9 @@ private string CreateCaretStopsString()

private int _glyphClusterInitialOffset;

private double _advanceWidthRoundingError;
private double _currentAdvanceTotal;

private double _idealAdvanceTotal;

private IList<ushort> _clusters;

Expand Down