Add missing attributes for AlphaPanel panel

#430

Source/Engine/UI/GUI/Panels/AlphaPanel.cs

@@ -1,6 +1,4 @@
-using System;
-using System.Collections.Generic;
-using FlaxEngine;
+// Copyright (c) 2012-2021 Wojciech Figat. All rights reserved.
 
 namespace FlaxEngine.GUI
 {
@@ -10,12 +8,15 @@ namespace FlaxEngine.GUI
     public class AlphaPanel : ContainerControl
     {
         /// <summary>
-        /// The target alpha value
+        /// The target alpha value.
         /// </summary>
-        public float Alpha;
+        [EditorOrder(0), Limit(0, 1, 0.01f), Tooltip("The target alpha value.")]
+        public float Alpha = 1.0f;
+
         /// <summary>
-        /// Whether or not we should ignore previous alphas
+        /// Whether or not we should ignore previous alphas.
         /// </summary>
+        [EditorOrder(10), Tooltip("Whether or not we should ignore previous alphas.")]
         public bool IgnoreStack;
 
         /// <inheritdoc/>
@@ -32,8 +33,9 @@ namespace FlaxEngine.GUI
                 Color newColor = new Color(oldColor.R, oldColor.G, oldColor.B, oldColor.A * Alpha);
                 Render2D.PushTint(ref newColor, false);
             }
+
             base.Draw();
-            
+
             Render2D.PopTint();
         }
     }