Fix memory leaks in Resource and Document caching

Add image/font/fontDefinition caches to Resource to prevent
allocating new native objects on every call. Destroy cached
Texture2D objects in Document.clearCache() to free GPU memory.

Author: CreepGin

Runtime/Dom/Document.cs

@@ -138,6 +138,9 @@ public Dom getDomFromVE(VisualElement ve) {
         }
 
         public void clearCache() {
+            foreach (var tex in _imageCache.Values) {
+                if (tex != null) Object.Destroy(tex);
+            }
             _imageCache.Clear();
             _fontCache.Clear();
             _fontDefinitionCache.Clear();

Runtime/Engine/Globals/Resource.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
 using UnityEngine;
 using UnityEngine.UIElements;
@@ -8,33 +9,46 @@ namespace OneJS {
 
     public class Resource {
         IScriptEngine _engine;
+        Dictionary<string, Texture2D> _imageCache = new();
+        Dictionary<string, Font> _fontCache = new();
+        Dictionary<string, FontDefinition> _fontDefinitionCache = new();
 
         public Resource(IScriptEngine engine) {
             _engine = engine;
         }
 
         public Font loadFont(string path) {
-            path = Path.IsPathRooted(path)
+            var fullPath = Path.IsPathRooted(path)
                 ? path
                 : Path.GetFullPath(Path.Combine(_engine.WorkingDir, path));
-            var font = new Font(path);
+            if (_fontCache.TryGetValue(fullPath, out var cached))
+                return cached;
+            var font = new Font(fullPath);
+            _fontCache[fullPath] = font;
             return font;
         }
 
         public FontDefinition loadFontDefinition(string path) {
-            path = Path.IsPathRooted(path)
+            var fullPath = Path.IsPathRooted(path)
                 ? path
                 : Path.GetFullPath(Path.Combine(_engine.WorkingDir, path));
-            var font = new Font(path);
-            return FontDefinition.FromFont(font);
+            if (_fontDefinitionCache.TryGetValue(fullPath, out var cached))
+                return cached;
+            var font = loadFont(path);
+            var fd = FontDefinition.FromFont(font);
+            _fontDefinitionCache[fullPath] = fd;
+            return fd;
         }
 
         public Texture2D loadImage(string path) {
-            path = Path.IsPathRooted(path) ? path : Path.Combine(_engine.WorkingDir, path);
-            var rawData = System.IO.File.ReadAllBytes(path);
-            Texture2D tex = new Texture2D(2, 2); // Create an empty Texture; size doesn't matter
+            var fullPath = Path.IsPathRooted(path) ? path : Path.Combine(_engine.WorkingDir, path);
+            if (_imageCache.TryGetValue(fullPath, out var cached))
+                return cached;
+            var rawData = System.IO.File.ReadAllBytes(fullPath);
+            Texture2D tex = new Texture2D(2, 2);
             tex.LoadImage(rawData);
             tex.filterMode = FilterMode.Bilinear;
+            _imageCache[fullPath] = tex;
             return tex;
         }
     }