Add Alignment option to Vertical and Horizonal Panels

#2599

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

@@ -80,6 +80,24 @@ namespace FlaxEngine.GUI
                     size.Y = maxHeight;
                 Size = size;
             }
+            else if (_alignment != TextAlignment.Near && hasAnyLeft)
+            {
+                // Apply layout alignment
+                var offset = Width - left - _margin.Right;
+                if (_alignment == TextAlignment.Center)
+                    offset *= 0.5f;
+                for (int i = 0; i < _children.Count; i++)
+                {
+                    Control c = _children[i];
+                    if (c.Visible)
+                    {
+                        if (Mathf.IsZero(c.AnchorMin.X) && Mathf.IsZero(c.AnchorMax.X))
+                        {
+                            c.X += offset;
+                        }
+                    }
+                }
+            }
         }
     }
 }

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

@@ -30,6 +30,11 @@ namespace FlaxEngine.GUI
         /// </summary>
         protected Float2 _offset;
 
+        /// <summary>
+        /// The child controls alignment within layout area.
+        /// </summary>
+        protected TextAlignment _alignment = TextAlignment.Near;
+
         /// <summary>
         /// Gets or sets the left margin.
         /// </summary>
@@ -172,6 +177,23 @@ namespace FlaxEngine.GUI
             }
         }
 
+        /// <summary>
+        /// Gets or sets the child controls alignment within layout area.
+        /// </summary>
+        [EditorOrder(50), VisibleIf(nameof(AutoSize), true)]
+        public TextAlignment Alignment
+        {
+            get => _alignment;
+            set
+            {
+                if (_alignment != value)
+                {
+                    _alignment = value;
+                    PerformLayout();
+                }
+            }
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="PanelWithMargins"/> class.
         /// </summary>

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

@@ -80,6 +80,24 @@ namespace FlaxEngine.GUI
                     size.X = maxWidth;
                 Size = size;
             }
+            else if (_alignment != TextAlignment.Near && hasAnyTop)
+            {
+                // Apply layout alignment
+                var offset = Height - top - _margin.Bottom;
+                if (_alignment == TextAlignment.Center)
+                    offset *= 0.5f;
+                for (int i = 0; i < _children.Count; i++)
+                {
+                    Control c = _children[i];
+                    if (c.Visible)
+                    {
+                        if (Mathf.IsZero(c.AnchorMin.Y) && Mathf.IsZero(c.AnchorMax.Y))
+                        {
+                            c.Y += offset;
+                        }
+                    }
+                }
+            }
         }
     }
 }