Avoid a globally shared SheetBuilder in SpriteFont.

A globally shared sheet builder leaks memory and resources between mod switches. Instead, we create and inject the sheet builder during mod startup to ensure we still share the builder across all fonts, but can reclaim it when the mod is unloaded.

OpenRA.Game/Graphics/SpriteFont.cs

@@ -19,26 +19,27 @@ namespace OpenRA.Graphics
 {
 	public class SpriteFont
 	{
-		static Library library = new Library();
-		static SheetBuilder builder;
+		static readonly Library Library = new Library();
 
 		readonly int size;
-
+		readonly SheetBuilder builder;
 		readonly Func<string, float> lineWidth;
+		readonly Face face;
+		readonly Cache<Pair<char, Color>, GlyphInfo> glyphs;
 
-		public SpriteFont(string name, int size)
+		public SpriteFont(string name, int size, SheetBuilder builder)
 		{
-			this.size = size;
+			if (builder.Type != SheetType.BGRA)
+				throw new ArgumentException("The sheet builder must create BGRA sheets.", "builder");
 
-			face = new Face(library, name);
+			this.size = size;
+			this.builder = builder;
+
+			face = new Face(Library, name);
 			face.SetPixelSizes((uint)size, (uint)size);
 
 			glyphs = new Cache<Pair<char, Color>, GlyphInfo>(CreateGlyph, Pair<char, Color>.EqualityComparer);
 
-			// setup a SheetBuilder for our private use
-			// TODO: SheetBuilder state is leaked between mod switches
-			if (builder == null)
-				builder = new SheetBuilder(SheetType.BGRA);
 			Func<char, float> characterWidth = character => glyphs[Pair.New(character, Color.White)].Advance;
 			lineWidth = line => line.Sum(characterWidth);
 
@@ -96,9 +97,6 @@ namespace OpenRA.Graphics
 			return new int2((int)Math.Ceiling(lines.Max(lineWidth)), lines.Length * size);
 		}
 
-		Cache<Pair<char, Color>, GlyphInfo> glyphs;
-		Face face;
-
 		GlyphInfo CreateGlyph(Pair<char, Color> c)
 		{
 			face.LoadChar(c.First, LoadFlags.Default, LoadTarget.Normal);