Add ImguiComboBox (dropdown list for GUILayout windows and areas)

src/Shared.Core/Shared.Core.projitems

@@ -28,6 +28,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Maker\UI\BaseGuiEntry.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Maker\UI\Sidebar\ISidebarControl.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)SceneApi.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Utilities\IMGUI\ImguiComboBox.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Utilities\IMGUI\ImguiWindow.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Utilities\TimelineCompatibility.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Utilities\ConfigurationManagerAttributes.cs" />

src/Shared.Core/Utilities/IMGUI/ImguiComboBox.cs

@@ -0,0 +1,171 @@
+// Popup list created by Eric Haines
+// ComboBox Extended by Hyungseok Seo.(Jerry) sdragoon@nate.com
+// this oop version of ComboBox is refactored by zhujiangbo jumbozhu@gmail.com
+// Modified by MarC0 / ManlyMarco
+
+using System;
+using UnityEngine;
+
+namespace KKAPI.Utilities
+{
+    /// <summary>
+    /// Dropdown control for use in GUILayout areas and windows. Keep the instance and call Show on it to draw it inside OnGUI.
+    /// Remember to call `DrawDropdownIfOpen` at the very end of the OnGUI area/window to actually display the dropdown list if it's open.
+    /// Only one dropdown list can be open globally. If a new dropdown is opened, all others are closed without changing the selected index.
+    /// </summary>
+    public class ImguiComboBox
+    {
+        private static ImguiComboBox _visibleBox;
+
+        private Vector2 _scrollPosition = Vector2.zero;
+        private GUIContent[] _cachedContents;
+
+        private int _newIndex;
+        private bool _wasChanged;
+
+        /// <summary>
+        /// Show a button that when clicked opens a dropdown list. Returns new index if user selected a different option, or the old index.
+        /// Warning: The list itself is not drawn here, you have to call DrawDropdownIfOpen at the end of your GUILayout area/window.
+        /// </summary>
+        /// <param name="selectedIndex">Currently selected item from the content list. It will be shown on the button.</param>
+        /// <param name="listContent">All items shown in the dropdown list when it is open.</param>
+        /// <param name="windowYmax">How low the dropdown can reach. Used to prevent the dropdown from extending off-screen. Set it to the GUILayout.Window rect yMax value.</param>
+        /// <param name="listStyle">Optional style of list buttons. By default the standard button style is used.</param>
+        public int Show(int selectedIndex, GUIContent[] listContent, int windowYmax = int.MaxValue, GUIStyle listStyle = null)
+        {
+            var content = selectedIndex >= 0 && selectedIndex < listContent.Length ? listContent[selectedIndex] : null;
+
+            Show(content, () => listContent, i =>
+            {
+                _newIndex = i;
+                _wasChanged = true;
+            }, windowYmax, listStyle);
+
+            if (_wasChanged)
+            {
+                GUI.changed = true;
+                _wasChanged = false;
+                return _newIndex;
+            }
+
+            return selectedIndex;
+        }
+
+        /// <summary>
+        /// Show a button that when clicked opens a dropdown list.
+        /// Warning: The list itself is not drawn here, you have to call DrawDropdownIfOpen at the end of your GUILayout area/window.
+        /// </summary>
+        /// <param name="selectedContent">Content shown on the button. It will also be selected in the dropdown list if it exists.</param>
+        /// <param name="getListContent">Called once to get the list contents when the button is clicked. It should return contents of the dropdown list, including <paramref name="selectedContent"/>.</param>
+        /// <param name="onIndexChanged">Called when user selects a new item</param>
+        /// <param name="windowYmax"></param>
+        /// <param name="listStyle"></param>
+        public void Show(GUIContent selectedContent, Func<GUIContent[]> getListContent, Action<int> onIndexChanged, int windowYmax = int.MaxValue, GUIStyle listStyle = null)
+        {
+            if (getListContent == null) throw new ArgumentNullException(nameof(getListContent));
+            if (onIndexChanged == null) throw new ArgumentNullException(nameof(onIndexChanged));
+
+            if (listStyle == null) listStyle = GUI.skin.button;
+            var content = selectedContent ?? GUIContent.none;
+
+            var rect = GUILayoutUtility.GetRect(content, listStyle, GUILayout.ExpandWidth(true));
+
+            var originalChanged = GUI.changed;
+
+            var done = false;
+            var controlId = GUIUtility.GetControlID(FocusType.Passive);
+
+            var currentMousePosition = Vector2.zero;
+            if (Event.current.GetTypeForControl(controlId) == EventType.MouseUp)
+            {
+                if (_visibleBox == this)
+                {
+                    done = true;
+                    currentMousePosition = Event.current.mousePosition;
+                }
+            }
+
+            if (GUI.Button(rect, content, listStyle))
+            {
+                _visibleBox = this;
+                _cachedContents = getListContent();
+            }
+
+            if (_visibleBox == this)
+            {
+                GUI.enabled = false;
+                GUI.color = new Color(1, 1, 1, 2);
+
+                _dropdownLocation = GUIUtility.GUIToScreenPoint(new Vector2(rect.x, rect.y + listStyle.CalcHeight(_cachedContents[0], 1.0f)));
+                var size = new Vector2(rect.width, listStyle.CalcHeight(_cachedContents[0], 1.0f) * _cachedContents.Length);
+
+                _innerRect = new Rect(0, 0, size.x, size.y);
+
+                _outerRectScreen = new Rect(_dropdownLocation.x, _dropdownLocation.y, size.x, size.y);
+                if (_outerRectScreen.yMax > windowYmax)
+                {
+                    _outerRectScreen.height = windowYmax - _outerRectScreen.y;
+                    _outerRectScreen.width += 20;
+                }
+
+                if (selectedContent == null)
+                    _selectedItem = -1;
+                else
+                    _selectedItem = Array.FindIndex(_cachedContents, c => c.text == selectedContent.text && c.image == selectedContent.image);
+
+                _onIndexChanged = onIndexChanged;
+
+                if (currentMousePosition != Vector2.zero && _outerRectScreen.Contains(GUIUtility.GUIToScreenPoint(currentMousePosition)))
+                    done = false;
+            }
+
+            if (done)
+                _visibleBox = null;
+
+            GUI.changed = originalChanged;
+        }
+
+        private Action<int> _onIndexChanged;
+        private int _selectedItem;
+        private Vector2 _dropdownLocation;
+        private Rect _outerRectScreen;
+        private Rect _innerRect;
+
+        private void DrawDropdownList()
+        {
+            GUI.enabled = true;
+
+            var scrpos = GUIUtility.ScreenToGUIPoint(_dropdownLocation);
+            var outerRectLocal = new Rect(scrpos.x, scrpos.y, _outerRectScreen.width, _outerRectScreen.height);
+
+            IMGUIUtils.DrawSolidBox(outerRectLocal);
+
+            _scrollPosition = GUI.BeginScrollView(outerRectLocal, _scrollPosition, _innerRect, false, false);
+            {
+                var newSelectedItemIndex = GUI.SelectionGrid(_innerRect, _selectedItem, _cachedContents, 1);
+                if (newSelectedItemIndex != _selectedItem)
+                {
+                    _onIndexChanged(newSelectedItemIndex);
+                    _visibleBox = null;
+                }
+            }
+            GUI.EndScrollView(true);
+        }
+
+        /// <summary>
+        /// Draws the dropdown list on top of all other window controls if it is open.
+        /// This should always be called at the very end of area/window that `Show` was called in.
+        /// Returns true if the dropdown list was opened and subsequently drawn.
+        /// </summary>
+        public bool DrawDropdownIfOpen()
+        {
+            if (_visibleBox == this)
+            {
+                _visibleBox.DrawDropdownList();
+                return true;
+            }
+
+            return false;
+        }
+    }
+}