Fixed typo

# Conflicts:
#	QuestPDF/Elements/Text/Items/TextBlockSpan.cs
#	QuestPDF/Fluent/TextStyleExtensions.cs
#	QuestPDF/Infrastructure/TextStyle.cs

QuestPDF.Examples/TextBenchmark.cs

@@ -111,7 +111,7 @@ namespace QuestPDF.Examples
             {
                 page.Margin(50);
                 
-                page.Content().Column(column =>
+                page.Content().PaddingVertical(10).Column(column =>
                 {
                     column.Item().Element(Title);
                     column.Item().PageBreak();

QuestPDF.Examples/TextExamples.cs

@@ -2,6 +2,7 @@
 using System.Linq;
 using System.Text;
 using NUnit.Framework;
+using QuestPDF.Elements.Text;
 using QuestPDF.Examples.Engine;
 using QuestPDF.Fluent;
 using QuestPDF.Helpers;
@@ -618,5 +619,43 @@ namespace QuestPDF.Examples
                         .FontSize(20);
                 });
         }
+        
+        [Test]
+        public void FontFallback()
+        {
+            RenderingTest
+                .Create()
+                .ProduceImages()
+                .ShowResults()
+                .RenderDocument(container =>
+                {
+                    container.Page(page =>
+                    {
+                        page.Margin(50);
+                        page.PageColor(Colors.White);
+                        page.DefaultTextStyle(x => x
+                            .Fallback(y => y.FontFamily("Segoe UI Emoji")
+                                .Fallback(y => y.FontFamily("Microsoft YaHei"))));
+
+                        page.Size(PageSizes.A4);
+
+                        page.Content().Text(t =>
+                        {
+                            t.Line("This is normal text.");
+                            t.EmptyLine();
+                            
+                            t.Line("Following line should use font fallback:");
+                            t.Line("中文文本");
+                            t.EmptyLine();
+                            
+                            t.Line("The following line contains a mix of known and unknown characters.");
+                            t.Line("Mixed line: This 中文 is 文文 a mixed 本 本 line 本 中文文本!");
+                            t.EmptyLine();
+
+                            t.Line("Emojis work out of the box because of font fallback: 😊😅🥳👍❤😍👌");
+                        });
+                    });
+                });
+        }
     }
 }

QuestPDF.Previewer/QuestPDF.Previewer.csproj

@@ -4,7 +4,7 @@
         <Authors>MarcinZiabek</Authors>
         <Company>CodeFlint</Company>
         <PackageId>QuestPDF.Previewer</PackageId>
-        <Version>2022.8.0</Version>
+        <Version>2022.9.0</Version>
         <PackAsTool>true</PackAsTool>
         <ToolCommandName>questpdf-previewer</ToolCommandName>
         <PackageDescription>QuestPDF is an open-source, modern and battle-tested library that can help you with generating PDF documents by offering friendly, discoverable and predictable C# fluent API.</PackageDescription>

QuestPDF/Drawing/DocumentGenerator.cs

@@ -172,7 +172,7 @@ namespace QuestPDF.Drawing
                 {
                     if (textBlockItem is TextBlockSpan textSpan)
                     {
-                        textSpan.Style = textSpan.Style.ApplyGlobalStyle(TextStyle.LibraryDefault);
+                        textSpan.Style = textSpan.Style.ApplyGlobalStyle(documentDefaultTextStyle);
                     }
                     else if (textBlockItem is TextBlockElement textElement)
                     {

QuestPDF/Drawing/Exceptions/DocumentDrawingException.cs

@@ -4,6 +4,11 @@ namespace QuestPDF.Drawing.Exceptions
 {
     public class DocumentDrawingException : Exception
     {
+        internal DocumentDrawingException(string message) : base(message)
+        {
+            
+        }
+        
         internal DocumentDrawingException(string message, Exception inner) : base(message, inner)
         {
             

QuestPDF/Drawing/TextMeasurement.cs

@@ -1,8 +0,0 @@
-namespace QuestPDF.Drawing
-{
-    internal struct TextMeasurement
-    {
-        public int LineIndex { get; set; }
-        public float FragmentWidth { get; set; }
-    }
-}

QuestPDF/Drawing/TextShaper.cs

@@ -55,9 +55,6 @@ namespace QuestPDF.Drawing
                 xOffset += glyphPositions[i].XAdvance * scaleX;
                 yOffset += glyphPositions[i].YAdvance * scaleY;
             }
-
-            if (Settings.CheckIfAllTextGlyphsAreAvailableInSpecifiedFont)
-                CheckIfAllGlyphsAreAvailable(glyphs, text);
             
             return new TextShapingResult(glyphs);
         }
@@ -78,20 +75,6 @@ namespace QuestPDF.Drawing
             else
                 throw new NotSupportedException("TextEncoding of type GlyphId is not supported.");
         }
-        
-        void CheckIfAllGlyphsAreAvailable(ShapedGlyph[] glyphs, string originalText)
-        {
-            var containsMissingGlyphs = glyphs.Any(x => x.Codepoint == default);
-            
-            if (!containsMissingGlyphs)
-                return;
-            
-            throw new ArgumentException(
-                $"Detected missing font glyphs while rendering text. " +
-                $"This means that the document contains text with characters not present in the assigned font. " +
-                $"Such characters are replaced by placeholders, usually visible as empty rectangles. " +
-                $"Font family used: {TextStyle.FontFamily}. Issue detected in text: '{originalText}'");
-        }
     }
     
     internal struct ShapedGlyph

QuestPDF/Elements/Text/FontFallback.cs

@@ -0,0 +1,150 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using QuestPDF.Drawing;
+using QuestPDF.Drawing.Exceptions;
+using QuestPDF.Elements.Text.Items;
+using QuestPDF.Fluent;
+using QuestPDF.Infrastructure;
+using SkiaSharp;
+
+namespace QuestPDF.Elements.Text
+{
+    internal static class FontFallback
+    {
+        public struct TextRun
+        {
+            public string Content { get; set; }
+            public TextStyle Style { get; set; }
+        }
+
+        public class FallbackOption
+        {
+            public TextStyle Style { get; set; }
+            public SKFont Font { get; set; }
+            public SKTypeface Typeface { get; set; }
+        }
+
+        private static SKFontManager FontManager => SKFontManager.Default;
+
+        public static IEnumerable<TextRun> SplitWithFontFallback(this string text, TextStyle textStyle)
+        {
+            var fallbackOptions = GetFallbackOptions(textStyle).ToArray();
+            
+            var spanStartIndex = 0;
+            var spanFallbackOption = fallbackOptions[0];
+            
+            for (var i = 0; i < text.Length; i += char.IsSurrogatePair(text, i) ? 2 : 1)
+            {
+                var codepoint = char.ConvertToUtf32(text, i);
+                var newFallbackOption = MatchFallbackOption(fallbackOptions, codepoint);
+
+                if (newFallbackOption == spanFallbackOption)
+                    continue;
+
+                yield return new TextRun
+                {
+                    Content = text.Substring(spanStartIndex, i - spanStartIndex),
+                    Style = spanFallbackOption.Style
+                };
+
+                spanStartIndex = i;
+                spanFallbackOption = newFallbackOption;
+            }
+            
+            if (spanStartIndex > text.Length)
+                yield break;
+            
+            yield return new TextRun
+            {
+                Content = text.Substring(spanStartIndex, text.Length - spanStartIndex),
+                Style = spanFallbackOption.Style
+            };
+
+            static IEnumerable<FallbackOption> GetFallbackOptions(TextStyle? textStyle)
+            {
+                while (textStyle != null)
+                {
+                    var font = textStyle.ToFont();
+                    
+                    yield return new FallbackOption
+                    {
+                        Style = textStyle,
+                        Font = font,
+                        Typeface = font.Typeface
+                    };
+
+                    textStyle = textStyle.Fallback;
+                }
+            }
+
+            static FallbackOption MatchFallbackOption(ICollection<FallbackOption> fallbackOptions, int codepoint)
+            {
+                foreach (var fallbackOption in fallbackOptions)
+                {
+                    if (fallbackOption.Font.ContainsGlyph(codepoint))
+                        return fallbackOption;
+                }
+
+                throw CreateNotMatchingFontException(codepoint);
+            }
+
+            static Exception CreateNotMatchingFontException(int codepoint)
+            {
+                var character = char.ConvertFromUtf32(codepoint);
+                var unicode = $"U-{codepoint:X4}";
+
+                var proposedFonts = FindFontsContainingGlyph(codepoint);
+                var proposedFontsFormatted = proposedFonts.Any() ? string.Join(", ", proposedFonts) : "no fonts available";
+                
+                return new DocumentDrawingException(
+                    $"Could not find an appropriate font fallback for glyph: {unicode} '{character}'. " +
+                    $"Font families available on current environment that contain this glyph: {proposedFontsFormatted}. " +
+                    $"Possible solutions: " +
+                    $"1) Use one of the listed fonts as the primary font in your document. " +
+                    $"2) Configure the fallback TextStyle using the 'TextStyle.Fallback' method with one of the listed fonts. ");
+            }
+            
+            static IEnumerable<string> FindFontsContainingGlyph(int codepoint)
+            {
+                var fontManager = SKFontManager.Default;
+
+                return fontManager
+                    .GetFontFamilies()
+                    .Select(fontManager.MatchFamily)
+                    .Where(x => x.ContainsGlyph(codepoint))
+                    .Select(x => x.FamilyName);
+            }
+        }
+
+        public static IEnumerable<ITextBlockItem> ApplyFontFallback(this ICollection<ITextBlockItem> textBlockItems)
+        {
+            foreach (var textBlockItem in textBlockItems)
+            {
+                if (textBlockItem is TextBlockSpan textBlockSpan and not TextBlockPageNumber)
+                {
+                    if (!Settings.CheckIfAllTextGlyphsAreAvailable && textBlockSpan.Style.Fallback == null)
+                    {
+                        yield return textBlockSpan;
+                        continue;
+                    }
+                    
+                    var textRuns = textBlockSpan.Text.SplitWithFontFallback(textBlockSpan.Style);
+
+                    foreach (var textRun in textRuns)
+                    {
+                        yield return new TextBlockSpan
+                        {
+                            Text = textRun.Content,
+                            Style = textRun.Style
+                        };
+                    }
+                }
+                else
+                {
+                    yield return textBlockItem;
+                }
+            }
+        }
+    }
+}

QuestPDF/Elements/Text/TextBlock.cs

@@ -18,8 +18,11 @@ namespace QuestPDF.Elements.Text
         private Queue<ITextBlockItem> RenderingQueue { get; set; }
         private int CurrentElementIndex { get; set; }
 
+        private bool FontFallbackApplied { get; set; } = false;
+        
         public void ResetState()
         {
+            ApplyFontFallback();
             InitializeQueue();
             CurrentElementIndex = 0;
 
@@ -37,6 +40,15 @@ namespace QuestPDF.Elements.Text
                 foreach (var item in Items)
                     RenderingQueue.Enqueue(item);
             }
+
+            void ApplyFontFallback()
+            {
+                if (FontFallbackApplied)
+                    return;
+
+                Items = Items.ApplyFontFallback().ToList();
+                FontFallbackApplied = true;
+            }
         }
 
         internal override SpacePlan Measure(Size availableSpace)

QuestPDF/Fluent/TextExtensions.cs

@@ -36,6 +36,7 @@ namespace QuestPDF.Fluent
         internal TextPageNumberDescriptor(Action<TextStyle> assignTextStyle, Action<PageNumberFormatter> assignFormatFunction) : base(assignTextStyle)
         {
             AssignFormatFunction = assignFormatFunction;
+            AssignFormatFunction(x => x?.ToString());
         }
 
         public TextPageNumberDescriptor Format(PageNumberFormatter formatter)

QuestPDF/Fluent/TextSpanDescriptorExtensions.cs

@@ -15,6 +15,17 @@ namespace QuestPDF.Fluent
             return descriptor;
         }
         
+        public static T Fallback<T>(this T descriptor, TextStyle? value = null) where T : TextSpanDescriptor
+        {
+            descriptor.TextStyle.Fallback = value;
+            return descriptor;
+        }
+        
+        public static T Fallback<T>(this T descriptor, Func<TextStyle, TextStyle> handler) where T : TextSpanDescriptor
+        {
+            return descriptor.Fallback(handler(TextStyle.Default));
+        }
+        
         public static T FontColor<T>(this T descriptor, string value) where T : TextSpanDescriptor
         {
             descriptor.MutateTextStyle(x => x.FontColor(value));

QuestPDF/Fluent/TextStyleExtensions.cs

@@ -4,8 +4,6 @@ using QuestPDF.Infrastructure;
 
 namespace QuestPDF.Fluent
 {
-    
-    
     public static class TextStyleExtensions
     {
         [Obsolete("This element has been renamed since version 2022.3. Please use the FontColor method.")]
@@ -131,6 +129,7 @@ namespace QuestPDF.Fluent
         #endregion
 
         #region Position
+        
         public static TextStyle NormalPosition(this TextStyle style)
         {
             return style.Position(FontPosition.Normal);
@@ -150,6 +149,21 @@ namespace QuestPDF.Fluent
         {
             return style.Mutate(TextStyleProperty.FontPosition, fontPosition);
         }
+        
+        #endregion
+
+        #region Fallback
+        
+        public static TextStyle Fallback(this TextStyle style, TextStyle? value = null)
+        {
+            return style.Mutate(TextStyleProperty.Fallback, value);
+        }
+        
+        public static TextStyle Fallback(this TextStyle style, Func<TextStyle, TextStyle> handler)
+        {
+            return style.Fallback(handler(TextStyle.Default));
+        }
+
         #endregion
     }
 }

QuestPDF/Infrastructure/TextStyle.cs

@@ -17,6 +17,8 @@ namespace QuestPDF.Infrastructure
         internal bool? HasUnderline { get; set; }
         internal bool? WrapAnywhere { get; set; }
 
+        internal TextStyle? Fallback { get; set; }
+
         internal static TextStyle LibraryDefault { get; } = new()
         {
             Color = Colors.Black,
@@ -29,7 +31,8 @@ namespace QuestPDF.Infrastructure
             IsItalic = false,
             HasStrikethrough = false,
             HasUnderline = false,
-            WrapAnywhere = false
+            WrapAnywhere = false,
+            Fallback = null
         };
 
         public static TextStyle Default { get; } = new();

QuestPDF/Infrastructure/TextStyleManager.cs

@@ -16,13 +16,15 @@ namespace QuestPDF.Infrastructure
         IsItalic,
         HasStrikethrough,
         HasUnderline,
-        WrapAnywhere
+        WrapAnywhere,
+        Fallback
     }
     
     internal static class TextStyleManager
     {
-        public static ConcurrentDictionary<(TextStyle origin, TextStyleProperty property, object value), TextStyle> TextStyleMutateCache = new();
-        public static ConcurrentDictionary<(TextStyle origin, TextStyle parent, bool overrideValue), TextStyle> TextStyleApplyCache = new();
+        private static readonly ConcurrentDictionary<(TextStyle origin, TextStyleProperty property, object value), TextStyle> TextStyleMutateCache = new();
+        private static readonly ConcurrentDictionary<(TextStyle origin, TextStyle parent), TextStyle> TextStyleApplyGlobalCache = new();
+        private static readonly ConcurrentDictionary<(TextStyle origin, TextStyle parent), TextStyle> TextStyleOverrideCache = new();
 
         public static TextStyle Mutate(this TextStyle origin, TextStyleProperty property, object value)
         {
@@ -30,7 +32,7 @@ namespace QuestPDF.Infrastructure
             return TextStyleMutateCache.GetOrAdd(cacheKey, x => MutateStyle(x.origin, x.property, x.value));
         }
 
-        private static TextStyle MutateStyle(TextStyle origin, TextStyleProperty property, object value, bool overrideValue = true)
+        private static TextStyle MutateStyle(TextStyle origin, TextStyleProperty property, object? value, bool overrideValue = true)
         {
             if (overrideValue && value == null)
                 return origin;
@@ -177,38 +179,69 @@ namespace QuestPDF.Infrastructure
                 
                 return origin with { WrapAnywhere = castedValue };
             }
+            
+            if (property == TextStyleProperty.Fallback)
+            {
+                if (!overrideValue && origin.Fallback != null)
+                    return origin;
+
+                var castedValue = (TextStyle?)value;
+                
+                if (origin.Fallback == castedValue)
+                    return origin;
+                
+                return origin with { Fallback = castedValue };
+            }
 
             throw new ArgumentOutOfRangeException(nameof(property), property, "Expected to mutate the TextStyle object. Provided property type is not supported.");
         }
         
         internal static TextStyle ApplyGlobalStyle(this TextStyle style, TextStyle parent)
         {
-            var cacheKey = (style, parent, false);
-            return TextStyleApplyCache.GetOrAdd(cacheKey, key => ApplyStyle(key.origin, key.parent, key.overrideValue));
+            var cacheKey = (style, parent);
+            return TextStyleApplyGlobalCache.GetOrAdd(cacheKey, key => ApplyStyle(key.origin, key.parent, overrideStyle: false).ApplyFontFallback());
+        }
+        
+        private static TextStyle ApplyFontFallback(this TextStyle style)
+        {
+            var targetFallbackStyle = style
+                ?.Fallback
+                ?.ApplyStyle(style, overrideStyle: false, applyFallback: false)
+                ?.ApplyFontFallback();
+            
+            return MutateStyle(style, TextStyleProperty.Fallback, targetFallbackStyle);
         }
         
         internal static TextStyle OverrideStyle(this TextStyle style, TextStyle parent)
         {
-            var cacheKey = (style, parent, true);
-            return TextStyleApplyCache.GetOrAdd(cacheKey, key => ApplyStyle(key.origin, key.parent, key.overrideValue));
+            var cacheKey = (style, parent);
+            
+            return TextStyleOverrideCache.GetOrAdd(cacheKey, key =>
+            {
+                var result = ApplyStyle(key.origin, key.parent);
+                return MutateStyle(result, TextStyleProperty.Fallback, key.parent.Fallback);
+            });
         }
         
-        private static TextStyle ApplyStyle(TextStyle style, TextStyle parent, bool overrideValue)
+        private static TextStyle ApplyStyle(this TextStyle style, TextStyle parent, bool overrideStyle = true, bool applyFallback = true)
         {
             var result = style;
 
-            result = MutateStyle(result, TextStyleProperty.Color, parent.Color, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.BackgroundColor, parent.BackgroundColor, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.FontFamily, parent.FontFamily, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.Size, parent.Size, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.LineHeight, parent.LineHeight, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.FontWeight, parent.FontWeight, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.FontPosition, parent.FontPosition, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.IsItalic, parent.IsItalic, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.HasStrikethrough, parent.HasStrikethrough, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.HasUnderline, parent.HasUnderline, overrideValue);
-            result = MutateStyle(result, TextStyleProperty.WrapAnywhere, parent.WrapAnywhere, overrideValue);
+            result = MutateStyle(result, TextStyleProperty.Color, parent.Color, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.BackgroundColor, parent.BackgroundColor, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.FontFamily, parent.FontFamily, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.Size, parent.Size, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.LineHeight, parent.LineHeight, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.FontWeight, parent.FontWeight, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.FontPosition, parent.FontPosition, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.IsItalic, parent.IsItalic, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.HasStrikethrough, parent.HasStrikethrough, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.HasUnderline, parent.HasUnderline, overrideStyle);
+            result = MutateStyle(result, TextStyleProperty.WrapAnywhere, parent.WrapAnywhere, overrideStyle);
             
+            if (applyFallback)
+                result = MutateStyle(result, TextStyleProperty.Fallback, parent.Fallback, overrideStyle);
+
             return result;
         }
     }

QuestPDF/Previewer/PreviewerService.cs

@@ -19,7 +19,7 @@ namespace QuestPDF.Previewer
         public  event Action? OnPreviewerStopped;
 
         private const int RequiredPreviewerVersionMajor = 2022;
-        private const int RequiredPreviewerVersionMinor = 8;
+        private const int RequiredPreviewerVersionMinor = 9;
         
         public PreviewerService(int port)
         {

QuestPDF/QuestPDF.csproj

@@ -3,7 +3,7 @@
         <Authors>MarcinZiabek</Authors>
         <Company>CodeFlint</Company>
         <PackageId>QuestPDF</PackageId>
-        <Version>2022.8.2</Version>
+        <Version>2022.9.0-alpha1</Version>
         <PackageDescription>QuestPDF is an open-source, modern and battle-tested library that can help you with generating PDF documents by offering friendly, discoverable and predictable C# fluent API.</PackageDescription>
         <PackageReleaseNotes>$([System.IO.File]::ReadAllText("$(MSBuildProjectDirectory)/Resources/ReleaseNotes.txt"))</PackageReleaseNotes>
         <LangVersion>9</LangVersion>

QuestPDF/Resources/ReleaseNotes.txt

@@ -1,20 +1,6 @@
-2022.8.0:
-
-- Improved library performance,
-- Breaking change: changed default font from Calibri to an open-source Lato,
-- Default font files are included with the nuget package, making it safe to deploy on any environment,
-- Default font files are significantly smaller, so output document files should be smaller too (up to 20x reduction in size),
-- When requested font is not available on the runtime environment, library provides list of available fonts,
-- Fixed a rare layout overflow exception with the Inlined element,
-- Fixed a memory leak connected to the HarfBuzz library.
-
-
-2022.8.1:
-- Fixed: default text style does not always work
-- Fixed: page breaking rendering does not work in very specific corner cases
-- Stability improvements for text wrapping
-- Updated stability of rendering elements in negative space
-- Optimization for the Column element: do not measure child when available height is negative
-
-2022.8.2
-- Fixed: the Column element incorrectly renders zero-height elements.
+2022.9.0
+- Implemented font-fallback algorithm,
+- Introduced new Settings API,
+- Significantly reduced memory allocation cost for TextStyle objects,
+- Implemented optional checking if all font glyphs are available,
+- Minor text-rendering optimizations.

QuestPDF/Settings.cs

@@ -3,7 +3,7 @@
     public static class Settings
     {
         /// <summary>
-        /// This value represents the maximum lenght of the document that the library produces.
+        /// This value represents the maximum length of the document that the library produces.
         /// This is useful when layout constraints are too strong, e.g. one element does not fit in another.
         /// In such cases, the library would produce document of infinite length, consuming all available resources.
         /// To break the algorithm and save the environment, the library breaks the rendering process after reaching specified length of document.
@@ -35,6 +35,6 @@
         /// However, it provides hints that used fonts are not sufficient to produce correct results.
         /// </summary>
         /// <remarks>By default, this flag is enabled only when the debugger IS attached.</remarks>
-        public static bool CheckIfAllTextGlyphsAreAvailableInSpecifiedFont { get; set; } = System.Diagnostics.Debugger.IsAttached;
+        public static bool CheckIfAllTextGlyphsAreAvailable { get; set; } = System.Diagnostics.Debugger.IsAttached;
     }
 }