Make an attempt at improving dropdown performance

Dropdown performance tanks at around 3000 elements on my machine.
Performance decrease is noticeable at around 700 elements where fps
drops 10 frames below 60.

MultipleMaid's dropdown solution does not seem to have this problem but
recreating ideal situations in the Unity editor does not seem to yield
the same results where the performance between the two are similar at
around 40 fps when built and executed.

I've considered splitting larger dropdowns, particularly the ero 2
dropdown, into smaller chunks but this solution is not ideal as MM is
able to list the ~3500 elements without problem.

COM3D2.MeidoPhotoStudio.Plugin/MeidoPhotoStudio/GUI/Controls/DropDown.cs

@@ -152,7 +152,9 @@ namespace COM3D2.MeidoPhotoStudio.Plugin
         private static bool initialized = false;
         public static bool Visible { get; private set; }
         private static bool onScrollBar = false;
-        public static Rect dropdownRect;
+        public static Rect dropdownWindow;
+        private static Rect dropdownScrollRect;
+        private static Rect dropdownRect;
         public static Vector2 CalculateElementSize(string[] list)
         {
             if (!initialized) InitializeStyle();
@@ -188,26 +190,27 @@ namespace COM3D2.MeidoPhotoStudio.Plugin
 
             if (calculatedListHeight > heightBelow && heightAbove > heightBelow)
             {
-                dropdownRect = new Rect(buttonRect.x, buttonRect.y - rectHeight, rectWidth + 18, rectHeight);
+                dropdownWindow = new Rect(buttonRect.x, buttonRect.y - rectHeight, rectWidth + 18, rectHeight);
             }
             else
             {
                 if (calculatedListHeight > heightBelow) rectHeight -= calculatedSize.y;
-                dropdownRect = new Rect(buttonRect.x, buttonRect.y + buttonRect.height, rectWidth + 18, rectHeight);
+                dropdownWindow = new Rect(buttonRect.x, buttonRect.y + buttonRect.height, rectWidth + 18, rectHeight);
             }
 
-            dropdownRect.x = Mathf.Clamp(dropdownRect.x, 0, Screen.width - rectWidth - 18);
+            dropdownWindow.x = Mathf.Clamp(dropdownWindow.x, 0, Screen.width - rectWidth - 18);
+
+            dropdownScrollRect = new Rect(0, 0, dropdownWindow.width, dropdownWindow.height);
+            dropdownRect = new Rect(0, 0, dropdownWindow.width - 18, calculatedListHeight);
 
             Visible = true;
         }
 
         public static void HandleDropdown()
         {
-            if (Visible)
-            {
-                GUILayout.Window(Constants.dropdownWindowID, dropdownRect, GUIFunc, "", windowStyle);
-            }
+            dropdownWindow = GUI.Window(Constants.dropdownWindowID, dropdownWindow, GUIFunc, "", windowStyle);
         }
+
         private static void GUIFunc(int id)
         {
             bool clicked = false;
@@ -217,16 +220,16 @@ namespace COM3D2.MeidoPhotoStudio.Plugin
                 clicked = true;
             }
 
-            scrollPos = GUILayout.BeginScrollView(scrollPos);
-            int selection = GUILayout.SelectionGrid(selectedItemIndex, dropdownList, 1, dropdownStyle);
-            GUILayout.EndScrollView();
+            scrollPos = GUI.BeginScrollView(dropdownScrollRect, scrollPos, dropdownRect);
+            int selection = GUI.SelectionGrid(dropdownRect, selectedItemIndex, dropdownList, 1, dropdownStyle);
+            GUI.EndScrollView();
 
             bool clickedYou = false;
             if (Utility.AnyMouseDown())
             {
                 Vector2 mousePos = GUIUtility.GUIToScreenPoint(Event.current.mousePosition);
-                bool clickedMe = dropdownRect.Contains(mousePos);
-                onScrollBar = mousePos.x > dropdownRect.x + dropdownRect.width - 12f;
+                bool clickedMe = dropdownWindow.Contains(mousePos);
+                onScrollBar = mousePos.x > dropdownWindow.x + dropdownWindow.width - 12f;
                 if (buttonRect.Contains(mousePos)) clickedYou = true;
                 if (!clickedMe) Visible = false;
             }

COM3D2.MeidoPhotoStudio.Plugin/MeidoPhotoStudio/Managers/WindowManager.cs

@@ -89,7 +89,7 @@ namespace COM3D2.MeidoPhotoStudio.Plugin
                 {
                     Vector2 mousePos = Event.current.mousePosition;
                     if (mainWindowVisible && mainWindowRect.Contains(mousePos)
-                        || dropdownVisible && DropdownHelper.dropdownRect.Contains(mousePos)
+                        || dropdownVisible && DropdownHelper.dropdownWindow.Contains(mousePos)
                         || messageWindowVisible && messageWindowRect.Contains(mousePos)
                     )
                     {
@@ -136,7 +136,7 @@ namespace COM3D2.MeidoPhotoStudio.Plugin
                 messageWindowRect = GUI.Window(Constants.messageWindowID, messageWindowRect, Windows[Window.Message].OnGUI, "", windowStyle);
             }
 
-            DropdownHelper.HandleDropdown();
+            if (DropdownHelper.Visible) DropdownHelper.HandleDropdown();
         }
     }
 }