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/Renderer.cs

@@ -37,6 +37,8 @@ namespace OpenRA.Graphics
 		readonly Queue<IVertexBuffer<Vertex>> tempBuffers = new Queue<IVertexBuffer<Vertex>>();
 		readonly Stack<Rectangle> scissorState = new Stack<Rectangle>();
 
+		SheetBuilder fontSheetBuilder;
+
 		Size? lastResolution;
 		int2? lastScroll;
 		float? lastZoom;
@@ -94,8 +96,13 @@ namespace OpenRA.Graphics
 		public void InitializeFonts(Manifest m)
 		{
 			using (new Support.PerfTimer("SpriteFonts"))
+			{
+				if (fontSheetBuilder != null)
+					fontSheetBuilder.Dispose();
+				fontSheetBuilder = new SheetBuilder(SheetType.BGRA);
 				Fonts = m.Fonts.ToDictionary(x => x.Key,
-					x => new SpriteFont(Platform.ResolvePath(x.Value.First), x.Value.Second)).AsReadOnly();
+					x => new SpriteFont(Platform.ResolvePath(x.Value.First), x.Value.Second, fontSheetBuilder)).AsReadOnly();
+			}
 		}
 
 		public void BeginFrame(int2 scroll, float zoom)
@@ -246,6 +253,8 @@ namespace OpenRA.Graphics
 			foreach (var buffer in tempBuffers)
 				buffer.Dispose();
 			tempBuffers.Clear();
+			if (fontSheetBuilder != null)
+				fontSheetBuilder.Dispose();
 		}
 	}
 }