Add feature load system fonts; Change default char to '□'

Author: ryancheung

samples/FontStashSharp.Samples.DynamicSpriteFont/Game1.cs

@@ -84,6 +84,8 @@ protected override void LoadContent()
 			// Simple
 			_fontSystem = new FontSystem();
 			_fontSystem.AddFont(File.ReadAllBytes(@"Fonts/DroidSans.ttf"));
+			_fontSystem.AddSystemFont("simsun");
+			_fontSystem.AddSystemFont("seguiemj");
 			_fontSystem.AddFont(File.ReadAllBytes(@"Fonts/DroidSansJapanese.ttf"));
 			_fontSystem.AddFont(File.ReadAllBytes(@"Fonts/Symbola-Emoji.ttf"));
 

src/FontStashSharp/FontSystem.cs

@@ -20,6 +20,8 @@ public partial class FontSystem : IDisposable
 
 		private FontAtlas _currentAtlas;
 
+		private readonly SystemFonts _systemFonts; 
+
 		public int TextureWidth => _settings.TextureWidth;
 		public int TextureHeight => _settings.TextureHeight;
 
@@ -46,6 +48,7 @@ public FontSystem(FontSystemSettings settings)
 			}
 
 			_settings = settings.Clone();
+			_systemFonts = new SystemFonts();
 
 			UseKernings = FontSystemDefaults.UseKernings;
 			DefaultCharacter = FontSystemDefaults.DefaultCharacter;
@@ -77,6 +80,17 @@ public void Dispose()
 			_fonts.Clear();
 		}
 
+		public void AddSystemFont(string fileName, FT_Render_Mode_ renderMode = FT_RENDER_MODE_NORMAL)
+		{
+			var data = _systemFonts.GetFontData(fileName);
+
+			if (data.Length > 0)
+			{
+				var fontSource = FreeTypeLoader.Load(data, renderMode);
+				_fontSources.Add(fontSource);
+			}
+		}
+
 		public void AddFont(byte[] data, FT_Render_Mode_ renderMode = FT_RENDER_MODE_NORMAL)
 		{
 			var fontSource = FreeTypeLoader.Load(data, renderMode);

src/FontStashSharp/FontSystemDefaults.cs

@@ -56,7 +56,7 @@ public static float FontResolutionFactor
 		}
 
 		public static bool UseKernings { get; set; } = true;
-		public static int? DefaultCharacter { get; set; } = '�';
+		public static int? DefaultCharacter { get; set; } = '□';
 
 		public static int TextStyleLineHeight { get; set; } = 2;
 	}

src/FontStashSharp/SystemFonts.cs

@@ -0,0 +1,102 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+
+namespace FontStashSharp
+{
+    public class SystemFonts
+    {
+        private static readonly IReadOnlyCollection<string> StandardFontLocations;
+
+        private readonly IReadOnlyCollection<string> _searchDirectories;
+        private readonly IEnumerable<string> _paths;
+
+        static SystemFonts()
+        {
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+            {
+                StandardFontLocations = new[]
+                {
+                    @"%SYSTEMROOT%\Fonts",
+                    @"%APPDATA%\Microsoft\Windows\Fonts",
+                    @"%LOCALAPPDATA%\Microsoft\Windows\Fonts",
+                };
+            }
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            {
+                StandardFontLocations = new[]
+                {
+                    "%HOME%/.fonts/",
+                    "%HOME%/.local/share/fonts/",
+                    "/usr/local/share/fonts/",
+                    "/usr/share/fonts/",
+                };
+            }
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+            {
+                StandardFontLocations = new[]
+                {
+                    // As documented on "Mac OS X: Font locations and their purposes"
+                    // https://web.archive.org/web/20191015122508/https://support.apple.com/en-us/HT201722
+                    "%HOME%/Library/Fonts/",
+                    "/Library/Fonts/",
+                    "/System/Library/Fonts/",
+                    "/Network/Library/Fonts/",
+                };
+            }
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Create("Android")))
+            {
+                StandardFontLocations = new[]
+                {
+                    "/system/fonts/"
+                };
+            }
+            else
+            {
+                StandardFontLocations = Array.Empty<string>();
+            }
+        }
+
+        public SystemFonts()
+        {
+            string[] expanded = StandardFontLocations.Select(x => Environment.ExpandEnvironmentVariables(x)).ToArray();
+            string[] existingDirectories = expanded.Where(x => Directory.Exists(x)).ToArray();
+
+            // We do this to provide a consistent experience with case sensitive file systems.
+            _paths = existingDirectories
+                .SelectMany(x => Directory.EnumerateFiles(x, "*.*", SearchOption.AllDirectories))
+                .Where(x => Path.GetExtension(x).Equals(".ttf", StringComparison.OrdinalIgnoreCase)
+                            || Path.GetExtension(x).Equals(".ttc", StringComparison.OrdinalIgnoreCase)
+                            || Path.GetExtension(x).Equals(".otf", StringComparison.OrdinalIgnoreCase));
+
+            _searchDirectories = existingDirectories;
+        }
+
+        public byte[] GetFontData(string fileName)
+        {
+            if (string.IsNullOrEmpty(fileName))
+            {
+                throw new ArgumentException("Font name cannot be null or empty.", nameof(fileName));
+            }
+
+            foreach (string path in _paths)
+            {
+                if (Path.GetFileName(path).StartsWith(fileName, StringComparison.OrdinalIgnoreCase))
+                {
+                    try
+                    {
+                        return File.ReadAllBytes(path);
+                    }
+                    catch
+                    {
+                        return Array.Empty<byte>();
+                    }
+                }
+            }
+
+            return Array.Empty<byte>();
+        }
+    }
+}