feat(io): add Gravograph .CHR font reader with text-to-geometry

Add ChrFont, a reader for Gravograph .CHR engraving fonts, plus UI to
convert placed text into engraved geometry in the CAD converter.

The .CHR files are obfuscated with a single-byte XOR. Different
GravoStyle releases use different keys (0x2F in older versions, 0xCF in
the 7000 series, and others across the font library), so the key is
auto-detected from byte 1 of the file: the font name is ASCII stored as
UTF-16LE, so the high byte of its first character is 0x00 in plaintext
and the raw byte equals the key. This reads every font in a GravoStyle
install regardless of version, not just one hardcoded key.

UI: right-clicking a text item in EntityView raises TextConvertRequested;
CadConverterForm renders it via ChrFont with H/V alignment and adds the
result on an ENGRAVE layer.

Tests use Xunit.SkippableFact and a gitignored test-config.json so the
suite points at a local .CHR file without committing proprietary assets.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

OpenNest.Tests/IO/ChrFontTests.cs

@@ -0,0 +1,180 @@
+using OpenNest.Geometry;
+using OpenNest.IO;
+
+namespace OpenNest.Tests.IO;
+
+public class ChrFontTests
+{
+    private ChrFont LoadFont()
+    {
+        var path = TestConfig.GetExistingPath("ChrFontPath");
+        Skip.If(path == null, "ChrFontPath not configured in test-config.json or file not found");
+        return ChrFont.Read(path);
+    }
+
+    [SkippableFact]
+    public void Read_ParsesFontName()
+    {
+        var font = LoadFont();
+        Assert.Equal("US BLOCK 1L", font.Name);
+    }
+
+    [SkippableFact]
+    public void Read_ParsesVersion()
+    {
+        var font = LoadFont();
+        Assert.StartsWith("C1.", font.Version);
+    }
+
+    [SkippableFact]
+    public void Read_HasAsciiGlyphs()
+    {
+        var font = LoadFont();
+        Assert.True(font.HasGlyph('A'));
+        Assert.True(font.HasGlyph('Z'));
+        Assert.True(font.HasGlyph('0'));
+        Assert.True(font.HasGlyph(' '));
+    }
+
+    [SkippableFact]
+    public void Read_HasExtendedGlyphs()
+    {
+        var font = LoadFont();
+        Assert.True(font.HasGlyph(0xC7)); // C-cedilla
+    }
+
+    [SkippableFact]
+    public void Glyph_L_ProducesLines()
+    {
+        var font = LoadFont();
+        var glyph = font.GetGlyph('L');
+        Assert.NotNull(glyph);
+
+        var entities = glyph.ToEntities(1.0, 0, 0);
+        Assert.True(entities.Count >= 2, $"Expected at least 2 entities for 'L', got {entities.Count}");
+        Assert.All(entities, e => Assert.Equal(EntityType.Line, e.Type));
+    }
+
+    [SkippableFact]
+    public void Glyph_O_ProducesEntities()
+    {
+        var font = LoadFont();
+        var glyph = font.GetGlyph('O');
+        Assert.NotNull(glyph);
+
+        var entities = glyph.ToEntities(1.0, 0, 0);
+        Assert.True(entities.Count > 0);
+    }
+
+    [SkippableFact]
+    public void RenderText_ProducesEntities()
+    {
+        var font = LoadFont();
+        var entities = font.RenderText("HELLO", 1.0, new Vector(0, 0));
+        Assert.True(entities.Count > 0, "RenderText should produce entities");
+    }
+
+    [SkippableFact]
+    public void RenderText_ScalesCorrectly()
+    {
+        var font = LoadFont();
+
+        var small = font.RenderText("A", 0.5, Vector.Zero);
+        var large = font.RenderText("A", 2.0, Vector.Zero);
+
+        var smallBox = small.GetBoundingBox();
+        var largeBox = large.GetBoundingBox();
+
+        Assert.True(largeBox.Width > smallBox.Width);
+        Assert.True(largeBox.Length > smallBox.Length);
+    }
+
+    [SkippableFact]
+    public void RenderText_AdvancesCursor()
+    {
+        var font = LoadFont();
+        var abEntities = font.RenderText("AB", 1.0, Vector.Zero);
+        var aEntities = font.RenderText("A", 1.0, Vector.Zero);
+
+        var abBox = abEntities.GetBoundingBox();
+        var aBox = aEntities.GetBoundingBox();
+
+        Assert.True(abBox.Length > aBox.Length * 1.5,
+            $"AB width ({abBox.Length:F1}) should be significantly wider than A width ({aBox.Length:F1})");
+    }
+
+    [SkippableFact]
+    public void RenderText_MatchesGravographReference()
+    {
+        var font = LoadFont();
+
+        var height = 5.08;
+        var centerX = 50.8;
+        var centerY = 34.925;
+
+        var entities = font.RenderText("Text", height, Vector.Zero);
+        var rawBox = entities.GetBoundingBox();
+        var shiftX = centerX - (rawBox.Left + rawBox.Right) / 2;
+        var shiftY = centerY - (rawBox.Top + rawBox.Bottom) / 2;
+        foreach (var e in entities)
+            e.Offset(new Vector(shiftX, shiftY));
+        Assert.True(entities.Count > 0, "Should produce entities for 'Text'");
+
+        var box = entities.GetBoundingBox();
+
+        var refLeft = 43.53;
+        var refRight = 58.07;
+        var refBottom = 32.39;
+        var refTop = 37.47;
+
+        var tolerance = 0.5;
+
+        Assert.True(System.Math.Abs(box.Left - refLeft) < tolerance,
+            $"Left: ours={box.Left:F2}, ref={refLeft:F2}, diff={System.Math.Abs(box.Left - refLeft):F2}");
+        Assert.True(System.Math.Abs(box.Right - refRight) < tolerance,
+            $"Right: ours={box.Right:F2}, ref={refRight:F2}, diff={System.Math.Abs(box.Right - refRight):F2}");
+        Assert.True(System.Math.Abs(box.Bottom - refBottom) < tolerance,
+            $"Bottom: ours={box.Bottom:F2}, ref={refBottom:F2}, diff={System.Math.Abs(box.Bottom - refBottom):F2}");
+        Assert.True(System.Math.Abs(box.Top - refTop) < tolerance,
+            $"Top: ours={box.Top:F2}, ref={refTop:F2}, diff={System.Math.Abs(box.Top - refTop):F2}");
+
+        var actualCapHeight = box.Top - box.Bottom;
+        Assert.True(System.Math.Abs(actualCapHeight - height) < 0.5,
+            $"Cap height: ours={actualCapHeight:F2}, expected={height:F2}");
+    }
+
+    [SkippableFact]
+    public void MeasureTextWidth_IsConsistent()
+    {
+        var font = LoadFont();
+        var height = 5.08;
+        var measuredWidth = font.MeasureTextWidth("Text", height);
+        var entities = font.RenderText("Text", height, Vector.Zero);
+        var box = entities.GetBoundingBox();
+
+        Assert.True(measuredWidth >= box.Length,
+            $"Measured={measuredWidth:F2} should be >= rendered={box.Length:F2}");
+        Assert.True(measuredWidth - box.Length < 2.0,
+            $"Measured={measuredWidth:F2}, rendered={box.Length:F2}, diff={measuredWidth - box.Length:F2}");
+    }
+
+    [SkippableFact]
+    public void Glyph_t_HasCurveAtBottom()
+    {
+        var font = LoadFont();
+        var glyph = font.GetGlyph('t');
+        Assert.NotNull(glyph);
+
+        var entities = glyph.ToEntities(1.0, 0, 0);
+        var lines = entities.Cast<Line>().ToList();
+
+        Assert.True(lines.Count >= 10, $"Expected at least 10 entities for 't', got {lines.Count}");
+
+        var curveLines = lines.Skip(1).Take(lines.Count - 3).ToList();
+        Assert.True(curveLines.Count >= 14, $"Expected at least 14 curve segments, got {curveLines.Count}");
+
+        var lastCurve = curveLines[^1];
+        Assert.True(lastCurve.EndPoint.X > curveLines[0].StartPoint.X,
+            $"Curve should end to the right of where it starts: start X={curveLines[0].StartPoint.X:F1}, end X={lastCurve.EndPoint.X:F1}");
+    }
+}

OpenNest.Tests/OpenNest.Tests.csproj

@@ -14,6 +14,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
     <PackageReference Include="xunit" Version="2.5.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.3" />
+    <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
   </ItemGroup>
 
   <ItemGroup>
@@ -38,6 +39,9 @@
     <Content Include="Splitting\TestData\**\*">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
+    <Content Include="test-config.json" Condition="Exists('test-config.json')">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
   </ItemGroup>
 
 </Project>

OpenNest.Tests/TestHelpers.cs

@@ -1,8 +1,37 @@
+using System.Text.Json;
 using OpenNest.CNC;
 using OpenNest.Geometry;
 
 namespace OpenNest.Tests;
 
+internal static class TestConfig
+{
+    private static readonly Lazy<Dictionary<string, string>> Config = new(() =>
+    {
+        var dir = AppContext.BaseDirectory;
+        for (var i = 0; i < 6; i++)
+        {
+            var path = Path.Combine(dir, "test-config.json");
+            if (File.Exists(path))
+            {
+                var json = File.ReadAllText(path);
+                return JsonSerializer.Deserialize<Dictionary<string, string>>(json) ?? new();
+            }
+            dir = Path.GetDirectoryName(dir)!;
+        }
+        return new();
+    });
+
+    public static string? Get(string key) =>
+        Config.Value.TryGetValue(key, out var val) ? val : null;
+
+    public static string? GetExistingPath(string key)
+    {
+        var path = Get(key);
+        return path != null && File.Exists(path) ? path : null;
+    }
+}
+
 internal static class TestHelpers
 {
     public static Part MakePartAt(double x, double y, double size = 1)