ParticleEffectForUGUI/Scripts/UIParticleOverlayCamera.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
#if UNITY_2018_3_OR_NEWER && UNITY_EDITOR
using PrefabStageUtility = UnityEditor.Experimental.SceneManagement.PrefabStageUtility;
#endif

namespace Coffee.UIExtensions
{
    /// <summary>
    /// </summary>
    [ExecuteInEditMode]
	[AddComponentMenu("")]
    public class UIParticleOverlayCamera : MonoBehaviour
    {
        //################################
        // Public/Protected Members.
        //################################
        /// <summary>
        /// Get instance object.
        /// If instance does not exist, Find instance in scene, or create new one.
        /// </summary>
        public static UIParticleOverlayCamera instance
        {
            get
            {
#if UNITY_2018_3_OR_NEWER && UNITY_EDITOR
                // If current scene is prefab mode, create OverlayCamera for editor.
                var prefabStage = PrefabStageUtility.GetCurrentPrefabStage();
                if (prefabStage != null && prefabStage.scene.isLoaded)
                {
                    if (!s_InstanceForPrefabMode)
                    {
                        // This GameObject is not saved in prefab.
                        // This GameObject is not shown in the hierarchy view.
                        // When you exit prefab mode, this GameObject is destroyed automatically.
                        var go = new GameObject(typeof(UIParticleOverlayCamera).Name + "_ForEditor")
                        {
                            hideFlags = HideFlags.HideAndDontSave,
                            tag = "EditorOnly",
                        };
                        UnityEngine.SceneManagement.SceneManager.MoveGameObjectToScene(go, prefabStage.scene);
                        s_InstanceForPrefabMode = go.AddComponent<UIParticleOverlayCamera>();
                    }
                    return s_InstanceForPrefabMode;
                }
#endif

                // Find instance in scene, or create new one.
                if (object.ReferenceEquals(s_Instance, null))
                {
                    s_Instance = FindObjectOfType<UIParticleOverlayCamera>() ?? new GameObject(typeof(UIParticleOverlayCamera).Name, typeof(UIParticleOverlayCamera)).GetComponent<UIParticleOverlayCamera>();
                    s_Instance.gameObject.SetActive(true);
                    s_Instance.enabled = true;
                }
                return s_Instance;
            }
        }

        public static Camera GetCameraForOvrelay(Canvas canvas)
        {
            var i = instance;
            var rt = canvas.rootCanvas.transform as RectTransform;
            var cam = i.cameraForOvrelay;
            var trans = i.transform;
            cam.enabled = false;

            var pos = rt.localPosition;
            cam.orthographic = true;
            cam.orthographicSize = Mathf.Max(pos.x, pos.y);
            cam.nearClipPlane = 0.3f;
            cam.farClipPlane = 1000f;
            pos.z -= 100;
            trans.localPosition = pos;

            return cam;
        }

        //################################
        // Private Members.
        //################################
        Camera cameraForOvrelay { get { return m_Camera ? m_Camera : (m_Camera = GetComponent<Camera>()) ? m_Camera : (m_Camera = gameObject.AddComponent<Camera>()); } }
        Camera m_Camera;
        static UIParticleOverlayCamera s_Instance;
#if UNITY_2018_3_OR_NEWER && UNITY_EDITOR
        static UIParticleOverlayCamera s_InstanceForPrefabMode;
#endif

        /// <summary>
        /// Awake is called when the script instance is being loaded.
        /// </summary>
        void Awake()
        {
#if UNITY_2018_3_OR_NEWER && UNITY_EDITOR
            // OverlayCamera for editor.
            if (hideFlags == HideFlags.HideAndDontSave || s_InstanceForPrefabMode == this)
            {
                s_InstanceForPrefabMode = GetComponent<UIParticleOverlayCamera>();
                return;
            }
#endif

            // Hold the instance.
            if (s_Instance == null)
            {
                s_Instance = GetComponent<UIParticleOverlayCamera>();
            }
            // If the instance is duplicated, destroy itself.
            else if (s_Instance != this)
            {
                UnityEngine.Debug.LogWarning("Multiple " + typeof(UIParticleOverlayCamera).Name + " in scene.", this.gameObject);
                enabled = false;
#if UNITY_EDITOR

                if (!Application.isPlaying)
                {
                    DestroyImmediate(gameObject);
                }
                else
#endif
                {
                    Destroy(gameObject);
                }
                return;
            }

            cameraForOvrelay.enabled = false;

            // Singleton has DontDestroy flag.
            if (Application.isPlaying)
            {
                DontDestroyOnLoad(gameObject);
            }
        }

        /// <summary>
        /// This function is called when the MonoBehaviour will be destroyed.
        /// </summary>
        void OnDestroy()
        {
#if UNITY_2018_3_OR_NEWER && UNITY_EDITOR
            if (s_InstanceForPrefabMode == this)
            {
                s_InstanceForPrefabMode = null;
            }
#endif

            // Clear instance on destroy.
            if (s_Instance == this)
            {
                s_Instance = null;
            }
        }
    }
}