Shows main component icon of a gameobject in the scene hierarchy panel, and also a toggle box to deactivate it

MainComponentIcon.cs

// Main Component Icon, Active State Toggling and "Smart Empty Object Icon Display"
using UnityEditor;
using UnityEngine;
using System;
using System.Collections.Generic;

[InitializeOnLoad]
class MainComponentIcon
{
	// only show these types if showAllTypes is false
	static Type[] componentTypes = new Type[]
	{
		typeof(Light),
		typeof(BoxCollider),
		typeof(Camera),
		typeof(ParticleSystem),
		typeof(TrailRenderer),
		typeof(MeshRenderer),
		typeof(MeshFilter),
		typeof(SpriteRenderer),
		typeof(AudioSource),
		typeof(Canvas),
		typeof(CanvasGroup),
		typeof(UnityEngine.UI.Image),
		typeof(UnityEngine.UI.Button),
		typeof(UnityEngine.UI.Text),

		// must add the custom types here if showAllTypes is false
		//typeof(GameController),
		//typeof(PlayerController)
	};
	static bool showActiveToggle = true;
	static bool showIndentedActiveToggle = false; // shows the idented gameobjects' toggle idented with their names
	static bool showAllTypes = true;
	static bool useFallbackIconForExcludedComponents = false;
	static bool prefabOverOthers = false; // don't show any component icon if the gameobject is a prefab, show the prefab icon instead
	static bool alwaysShowCustom = false; // will show all custom, even if they don't have custom images (will show the little script page icon)
	static bool alwaysShowPrefabContainer = false; // ?
	static IdleObjectsView showEmptyPrefabIconInIdleObjects = IdleObjectsView.TransformIcon; // // gameobjects with no child or components
	static FallbackIcon fallbackIcon = FallbackIcon.GameObjectOrTransformsOrPrefab;

	// UI exceptions
	static bool canvasOverPrefab = true;

	static List<GameObject> allChildGOsForToggle;
	static bool toggleActiveAllChildInheritToggleObject = true; // Attention: if hold alt and clickin on object toggle, it will set all childs active state to the same of the clicked object

	static MainComponentIcon()
	{
		// Init
		EditorApplication.hierarchyWindowItemOnGUI += HierarchyItemCB;
	}

	static void HierarchyItemCB(int instanceID, Rect selectionRect)
	{
		GameObject obj = EditorUtility.InstanceIDToObject(instanceID) as GameObject;

		if (obj)
		{
			var guiBackupColor = GUI.color;

			Rect r = new Rect(selectionRect);
			if (showActiveToggle)
			{
				// Toggle active button
				r.x = showIndentedActiveToggle ? selectionRect.x - 22 : 2;
				r.width = 18;
				r.height = 16;

				EditorGUI.BeginChangeCheck();

				if (!obj.activeInHierarchy) GUI.color = new Color(GUI.color.r, GUI.color.g, GUI.color.b, 0.3f);
				var toggleValue = GUI.Toggle(r, obj.activeSelf, "");
				GUI.color = guiBackupColor;

				if (Selection.objects.Length > 1 && Selection.objects [0] is GameObject)
				{
					if (EditorGUI.EndChangeCheck ())
					{
						var objsToToggle = new List<GameObject> ();
						foreach (var selObj in Selection.objects)
							objsToToggle.Add (selObj as GameObject);
						Undo.RecordObjects (objsToToggle.ToArray (), "Toggle GameObjects Active");
						objsToToggle.ForEach (child => child.SetActive (toggleValue));
						objsToToggle.Clear ();
					}
				}
				else
				{
					if (toggleActiveAllChildInheritToggleObject && Event.current.alt)
					{
						if (EditorGUI.EndChangeCheck())
						{
							if (allChildGOsForToggle == null) allChildGOsForToggle = new List<GameObject>();
							allChildGOsForToggle.Clear();
							allChildGOsForToggle.Add(obj);
							FetchAllChildGameObjects(obj.transform);
							Undo.RecordObjects(allChildGOsForToggle.ToArray(), "Toggle GameObjects Active");
							allChildGOsForToggle.ForEach(child => child.SetActive(toggleValue));
						}
					}
					else if (EditorGUI.EndChangeCheck())
					{
						Undo.RecordObject(obj, "Toggle " + obj.name + " Active");
						obj.SetActive(toggleValue);
					}
				}
			}

			// Icon
			r.x = EditorGUIUtility.currentViewWidth - 38;
			r.width = 18;
			r.height = 18;
			guiBackupColor = GUI.color;
			if (!obj.activeInHierarchy) GUI.color = new Color(GUI.color.r, GUI.color.g, GUI.color.b, 0.3f);
			var components = obj.GetComponents<Component>();
			if (components != null)
			{
				// FIRST COMPONENT IS ALWAYS TRANSFORM OR RECT TRASNFORM
				if (components.Length > 1)
				{
					// HAS COMPONENTS
					Type type = components[1].GetType();
					Texture image = EditorGUIUtility.ObjectContent(obj.GetComponent(type), type).image;
					bool isInComponentTypesList = Array.Exists(componentTypes, x => x == type);

					if (image == null)
					{
						// put your custom components icons in Assets/Editor/Icons, name it the same name of your class and change the extension below as accordingly
						image = AssetDatabase.LoadAssetAtPath("Assets/Editor/Icons/" + type.ToString() + ".psd", typeof(Texture)) as Texture;
					}

					if (canvasOverPrefab && type == typeof(Canvas))
					{
						GUI.Label(r, EditorGUIUtility.IconContent("Canvas Icon"));
					}
					else if (prefabOverOthers && CanShowAsPrefab(obj))
					{
						ShowFallbackIcon(obj, r);
					}
					else if (!image && alwaysShowCustom)
					{
						GUI.Label(r, EditorGUIUtility.IconContent("cs Script Icon"));
					}
					else if (showAllTypes || isInComponentTypesList)
					{
						if (image)
						{
							GUI.Label(r, image);
						}
						else
						{
							ShowFallbackIcon(obj, r);
						}
					}
					else if (image && useFallbackIconForExcludedComponents || alwaysShowPrefabContainer && CanShowAsPrefab(obj))
					{
						ShowFallbackIcon(obj, r);
					}
				}
				else
				{
					// IDLE OBJECTS
					if (obj.transform.childCount == 0)
					{
						if (CanShowAsPrefab(obj))
							GUI.Label(r, EditorGUIUtility.IconContent("PrefabNormal Icon"));
						else if (showEmptyPrefabIconInIdleObjects == IdleObjectsView.WhitePrefabIcon) // no child nor components
							GUI.Label(r, EditorGUIUtility.IconContent("Prefab Icon"));
						else if (showEmptyPrefabIconInIdleObjects == IdleObjectsView.TransformIcon) // no child nor components
						{
							if (obj.GetComponent<RectTransform>())
								GUI.Label(r, EditorGUIUtility.IconContent("RectTransform Icon"));
							else
								GUI.Label(r, EditorGUIUtility.IconContent("Transform Icon"));
						}
					}
					// NO COMPONENTS BUT HAS CHILDREN
					else if (obj.transform.childCount > 0)
					{
						if (CanShowAsPrefab(obj))
							GUI.Label(r, EditorGUIUtility.IconContent("PrefabNormal Icon"));
						else
							GUI.Label(r, EditorGUIUtility.IconContent("Prefab Icon"));

						GUI.Label(r, EditorGUIUtility.IconContent("Transform Icon"));
					}

				}
			}

			GUI.color = guiBackupColor;
		}
	}

	static void ShowFallbackIcon(GameObject obj, Rect r)
	{
		switch (fallbackIcon)
		{
		case FallbackIcon.TransformOrRect:

			if (obj.GetComponent<RectTransform>())
				GUI.Label(r, EditorGUIUtility.IconContent("RectTransform Icon"));
			else
				GUI.Label(r, EditorGUIUtility.IconContent("Transform Icon"));
			break;

		case FallbackIcon.GameObjectOrPrefab:
			if (CanShowAsPrefab(obj))
				GUI.Label(r, EditorGUIUtility.IconContent("PrefabNormal Icon"));
			else
				GUI.Label(r, EditorGUIUtility.IconContent("GameObject Icon"));
			break;

		case FallbackIcon.GameObjectOrTransformsOrPrefab:
			if (CanShowAsPrefab(obj))
				GUI.Label(r, EditorGUIUtility.IconContent("PrefabNormal Icon"));
			else
			{
				if (obj.GetComponents<Component>().Length > 1)
				{
					GUI.Label(r, EditorGUIUtility.IconContent("GameObject Icon"));
				}
				else
				{
					GUI.Label(r, EditorGUIUtility.IconContent("Transform Icon"));
				}
			}
			break;
		}
	}

	static bool IsPartOfPrefab(GameObject prefab)
	{
		return PrefabUtility.GetPrefabParent(prefab) != null;
	}

	static bool IsPrefabParent(GameObject prefab)
	{
		return PrefabUtility.FindPrefabRoot(prefab) == prefab;
	}

	static bool CanShowAsPrefab(GameObject prefab)
	{
		if (IsPrefabParent(prefab) &&
			IsPartOfPrefab(prefab) &&
			PrefabUtility.GetPrefabType(prefab) == PrefabType.PrefabInstance ||
			PrefabUtility.GetPrefabType(prefab) == PrefabType.ModelPrefabInstance)
		{
			return true;
		}

		return false;
	}

	public static void FetchAllChildGameObjects(Transform transform)
	{
		if (allChildGOsForToggle == null) allChildGOsForToggle = new List<GameObject>();
		foreach (Transform t in transform)
		{
			if (!allChildGOsForToggle.Contains(t.gameObject)) allChildGOsForToggle.Add(t.gameObject);
			FetchAllChildGameObjects(t);
		}
	}

	//static bool 
}

enum FallbackIcon
{
	None,
	GameObjectOrTransformsOrPrefab,
	GameObjectOrPrefab,
	TransformOrRect
}

enum IdleObjectsView
{
	None,
	TransformIcon,
	WhitePrefabIcon
}