Text: added fallback when font does not specify underline or strikeout configurations

Source/QuestPDF/Drawing/FontManager.cs

@@ -20,7 +20,7 @@ namespace QuestPDF.Drawing
     public static class FontManager
     {
         private static readonly ConcurrentDictionary<string, FontStyleSet> StyleSets = new();
-        private static readonly ConcurrentDictionary<TextStyle, SKFontMetrics> FontMetrics = new();
+        private static readonly ConcurrentDictionary<TextStyle, FontMetrics> FontMetrics = new();
         private static readonly ConcurrentDictionary<TextStyle, SKPaint> FontPaints = new();
         private static readonly ConcurrentDictionary<string, SKPaint> ColorPaints = new();
         private static readonly ConcurrentDictionary<TextStyle, Font> ShaperFonts = new();
@@ -214,9 +214,47 @@ namespace QuestPDF.Drawing
             }
         }
 
-        internal static SKFontMetrics ToFontMetrics(this TextStyle style)
+        internal static FontMetrics ToFontMetrics(this TextStyle style)
         {
-            return FontMetrics.GetOrAdd(style, key => key.NormalPosition().ToPaint().FontMetrics);
+            return FontMetrics.GetOrAdd(style, key =>
+            {
+                var skiaFontMetrics = key.NormalPosition().ToPaint().FontMetrics;
+                
+                return new FontMetrics
+                {
+                    Ascent = skiaFontMetrics.Ascent,
+                    Descent = skiaFontMetrics.Descent,
+                    
+                    UnderlineThickness = GetUnderlineThickness(),
+                    UnderlinePosition = GetUnderlinePosition(),
+                    
+                    StrikeoutThickness = GetStrikeoutThickness(),
+                    StrikeoutPosition = GetStrikeoutPosition()
+                };
+
+                // HACK: On MacOS, certain font metrics are not determined accurately.
+                // Provide defaults based on other metrics.
+                
+                float GetUnderlineThickness()
+                {
+                    return skiaFontMetrics.UnderlineThickness ?? (skiaFontMetrics.XHeight * 0.1f);
+                }
+                
+                float GetUnderlinePosition()
+                {
+                    return skiaFontMetrics.UnderlinePosition ?? (skiaFontMetrics.XHeight * 0.2f);
+                }
+                
+                float GetStrikeoutThickness()
+                {
+                    return skiaFontMetrics.StrikeoutThickness ?? (skiaFontMetrics.XHeight * 0.1f);
+                }
+                
+                float GetStrikeoutPosition()
+                {
+                    return skiaFontMetrics.StrikeoutPosition ?? (-skiaFontMetrics.XHeight * 0.5f);
+                }
+            });
         }
 
         internal static Font ToShaperFont(this TextStyle style)

Source/QuestPDF/Elements/Text/Items/TextBlockSpan.cs

@@ -148,19 +148,19 @@ namespace QuestPDF.Elements.Text.Items
                 request.Canvas.DrawText(textDrawingCommand.Value.SkTextBlob, new Position(textDrawingCommand.Value.TextOffsetX, glyphOffsetY), Style);
 
             // draw underline
-            if ((Style.HasUnderline ?? false) && fontMetrics.UnderlinePosition.HasValue)
+            if (Style.HasUnderline ?? false)
             {
                 var underlineOffset = Style.FontPosition == FontPosition.Superscript ? 0 : glyphOffsetY;
-                DrawLine(fontMetrics.UnderlinePosition.Value + underlineOffset, fontMetrics.UnderlineThickness ?? 1);
+                DrawLine(fontMetrics.UnderlinePosition + underlineOffset, fontMetrics.UnderlineThickness);
             }
             
             // draw stroke
-            if ((Style.HasStrikethrough ?? false) && fontMetrics.StrikeoutPosition.HasValue)
+            if (Style.HasStrikethrough ?? false)
             {
-                var strikeoutThickness = fontMetrics.StrikeoutThickness ?? 1;
+                var strikeoutThickness = fontMetrics.StrikeoutThickness;
                 strikeoutThickness *= Style.FontPosition == FontPosition.Normal ? 1f : 0.625f;
                 
-                DrawLine(fontMetrics.StrikeoutPosition.Value + glyphOffsetY, strikeoutThickness);
+                DrawLine(fontMetrics.StrikeoutPosition + glyphOffsetY, strikeoutThickness);
             }
             
             void DrawLine(float offset, float thickness)

Source/QuestPDF/Infrastructure/FontMetrics.cs

@@ -0,0 +1,13 @@
+namespace QuestPDF.Infrastructure;
+
+internal struct FontMetrics
+{
+    public float Ascent { get; set; }
+    public float Descent { get; set; }
+    
+    public float UnderlinePosition { get; set; }
+    public float UnderlineThickness { get; set; }
+    
+    public float StrikeoutPosition { get; set; }
+    public float StrikeoutThickness { get; set; }
+}