How do I generate glyph paths for strings containing characters that cannot be combined?

[mes51]

Hi. Thank you for fixing the WordBreaking.BreakAll and WrappingLength issues previously.

I am currently developing a function to randomly shift and draw the code point of each character in an input string.
When I tried to generate glyph paths with TextRenderer by combining characters with shifted code points, I encountered a NullReferenceException for some character combinations.
I understand that some characters cannot be combined to generate paths due to the random code point shifting, but I would like to skip the characters that cannot be generated in such cases and continue generating paths for other problem-free glyphs.
It is possible to generate paths one character at a time, but since I also want to use the WrappingLength setting, I would like to process all characters at once if possible.
When an exception occurs due to the appearance of a character that cannot be combined by shifting code points, is it possible to avoid this, or detect it and replace the target character with a space, etc.?

The following is a sample of the image we would like to generate with this feature, although it is a mock-up created in After Effects.

sample.mp4

Stacktrace

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at SixLabors.Fonts.Tables.AdvancedTypographic.Shapers.UniversalShaper.SetupSyllables(IGlyphShapingCollection collection, Int32 index, Int32 count)
   at SixLabors.Fonts.Tables.AdvancedTypographic.Shapers.ShapingStage.PreProcessFeature(IGlyphShapingCollection collection, Int32 index, Int32 count)
   at SixLabors.Fonts.Tables.AdvancedTypographic.GSubTable.ApplySubstitution(FontMetrics fontMetrics, GlyphSubstitutionCollection collection)
   at SixLabors.Fonts.StreamFontMetrics.ApplySubstitution(GlyphSubstitutionCollection collection)
   at SixLabors.Fonts.FileFontMetrics.ApplySubstitution(GlyphSubstitutionCollection collection)
   at SixLabors.Fonts.TextLayout.DoFontRun(ReadOnlySpan`1 text, Int32 start, IReadOnlyList`1 textRuns, Int32& textRunIndex, Int32& codePointIndex, Int32& bidiRunIndex, Boolean isFallbackRun, Font font, BidiRun[] bidiRuns, Dictionary`2 bidiMap, GlyphSubstitutionCollection substitutions, GlyphPositioningCollection positionings)
   at SixLabors.Fonts.TextLayout.ProcessText(ReadOnlySpan`1 text, TextOptions options)
   at SixLabors.Fonts.TextLayout.GenerateLayout(ReadOnlySpan`1 text, TextOptions options)
   at SixLabors.Fonts.TextRenderer.RenderText(ReadOnlySpan`1 text, TextOptions options)
   at SixLabors.Fonts.TextRenderer.RenderText(String text, TextOptions options)
   at SixLabors.Fonts.TextRenderer.RenderTextTo(IGlyphRenderer renderer, String text, TextOptions options)
   at Program.<Main>$(String[] args) in C:\dev\RandomCharacterTest\RandomCharacterTest\Program.cs:line 26

Steps to Reproduce

using SixLabors.Fonts;
using System.Numerics;
using System.Text;

var TaiLeCharacter = new Rune(0x195C);     // ᥜ
var SundaneseCharacter = new Rune(0x1B9B); // ᮛ
var TifinaghCharacter = new Rune(0x2D43);  // ⵃ
var ChamCharacter = new Rune(0xAA43);      // ꩃ

var LatainCharacter = new Rune(0x0041);    // A
var HiraganaCharacter = new Rune(0x3042);  // あ

var fontFamily = SystemFonts.Get("Yu Gothic");
var font = fontFamily.CreateFont(20.0F);
var textOption = new TextOptions(font);

// OK
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{TaiLeCharacter}{TaiLeCharacter}{TaiLeCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{SundaneseCharacter}{SundaneseCharacter}{SundaneseCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{TifinaghCharacter}{TifinaghCharacter}{TifinaghCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{ChamCharacter}{ChamCharacter}{ChamCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{LatainCharacter}{LatainCharacter}{LatainCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{HiraganaCharacter}{HiraganaCharacter}{HiraganaCharacter}", textOption);

// raise NullReferenceException
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{LatainCharacter}{TaiLeCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{HiraganaCharacter}{TaiLeCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{LatainCharacter}{SundaneseCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{HiraganaCharacter}{SundaneseCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{LatainCharacter}{TifinaghCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{HiraganaCharacter}{TifinaghCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{LatainCharacter}{ChamCharacter}", textOption);
TextRenderer.RenderTextTo(new DummyGlyphRenderer(), $"{HiraganaCharacter}{ChamCharacter}", textOption);

class DummyGlyphRenderer : IGlyphRenderer
{
    public void BeginFigure() { }

    public bool BeginGlyph(in FontRectangle bounds, in GlyphRendererParameters parameters) => true;

    public void BeginText(in FontRectangle bounds) { }

    public void CubicBezierTo(Vector2 secondControlPoint, Vector2 thirdControlPoint, Vector2 point) { }

    public TextDecorations EnabledDecorations() => new TextDecorations();

    public void EndFigure() { }

    public void EndGlyph() { }

    public void EndText() { }

    public void LineTo(Vector2 point) { }

    public void MoveTo(Vector2 point) { }

    public void QuadraticBezierTo(Vector2 secondControlPoint, Vector2 point) { }

    public void SetDecoration(TextDecorations textDecorations, Vector2 start, Vector2 end, float thickness) { }
}

System configuration

• Windows 11 Home 23H2
• .NET 7
• SixLabors.Fonts v2.0.2

[JimBobSquarePants]

Sorry! I didn't see this at all! Looking at this and #390 now

[mes51]

I have checked that this has been fixed in version 2.0.3.
Thank you for fixing this issue!