fixed collection access/modification

Scripts/Chunk.cs

@@ -17,6 +17,8 @@ public class Chunk {
     private readonly int sizeX;
     private readonly int sizeY;
     private readonly HashSet<Element> activeElements;
+    private readonly HashSet<Element> toAddElements = new();
+    private readonly HashSet<Element> toRemoveElements = new();
 
     public Chunk(int x, int y, int index) {
         Index = index;
@@ -37,15 +39,17 @@ public class Chunk {
     }
 
     public void Update() {
-        // for (int x = 0; x < sizeX; x++) {
-        //     for (int y = 0; y < sizeY; y++) {
-        //         if (Elements[x,y] != null)
-        //             Elements[x,y].Update();
-        //     }
-        // }
-        foreach (Element e in activeElements) {
+        foreach (Element e in activeElements)
             e.Update();
-        }
+
+        // apply changes:
+        foreach (Element removeElement in toRemoveElements)
+            activeElements.Remove(removeElement);
+        toRemoveElements.Clear();
+
+        foreach (Element addElement in toAddElements)
+            activeElements.Add(addElement);
+        toAddElements.Clear();
     }
 
     public void WritePixel<T>(int x, int y, int size) {
@@ -67,21 +71,9 @@ public class Chunk {
         }
     }
 
-    // TODO: use this function and stitch together partial images in Level
-    public Image DrawLevel() {
-        for (int x = 0; x < sizeX; x++) {
-            for (int y = 0; y < sizeY; y++) {
-                image.SetPixel(x,y, Elements[x,y].Color);
-            }
-        }
-        return image;
-    }
-
     public void SetElementActive(Element e, bool active) {
-        if (active && e.GetType() != typeof(Element))
-            activeElements.Add(e);
-        else
-            activeElements.Remove(e);
+        if (active) toAddElements.Add(e);
+        else toRemoveElements.Remove(e);
     }
 
     public int ActiveElemetnsCount() {