Add horizontal alignment tags for rich text box

Source/Engine/UI/GUI/Common/RichTextBox.Parsing.cs

@@ -91,6 +91,8 @@ namespace FlaxEngine.GUI
             { "size", ProcessSize },
             { "img", ProcessImage },
             { "valign", ProcessVAlign },
+            { "align", ProcessAlign },
+            { "center", ProcessCenter },
         };
 
         private HtmlParser _parser = new HtmlParser();
@@ -242,10 +244,12 @@ namespace FlaxEngine.GUI
             }
 
             // Organize text blocks within line
+            var horizontalAlignments = TextBlockStyle.Alignments.Baseline;
             for (int i = context.LineStartTextBlockIndex; i < _textBlocks.Count; i++)
             {
                 ref TextBlock textBlock = ref textBlocks[i];
                 var vOffset = lineSize.Y - textBlock.Bounds.Height;
+                horizontalAlignments |= textBlock.Style.Alignment & TextBlockStyle.Alignments.HorizontalMask;
                 switch (textBlock.Style.Alignment & TextBlockStyle.Alignments.VerticalMask)
                 {
                 case TextBlockStyle.Alignments.Baseline:
@@ -279,6 +283,24 @@ namespace FlaxEngine.GUI
                 }
                 }
             }
+            var hOffset = Width - lineSize.X;
+            if ((horizontalAlignments & TextBlockStyle.Alignments.Center) == TextBlockStyle.Alignments.Center)
+            {
+                hOffset *= 0.5f;
+                for (int i = context.LineStartTextBlockIndex; i < _textBlocks.Count; i++)
+                {
+                    ref TextBlock textBlock = ref textBlocks[i];
+                    textBlock.Bounds.Location.X += hOffset;
+                }
+            }
+            else if ((horizontalAlignments & TextBlockStyle.Alignments.Right) == TextBlockStyle.Alignments.Right)
+            {
+                for (int i = context.LineStartTextBlockIndex; i < _textBlocks.Count; i++)
+                {
+                    ref TextBlock textBlock = ref textBlocks[i];
+                    textBlock.Bounds.Location.X += hOffset;
+                }
+            }
 
             // Move to the next line
             context.LineStartCharacterIndex = lineEnd + 1;

Source/Engine/UI/GUI/Common/RichTextBox.Tags.cs

@@ -231,6 +231,49 @@ namespace FlaxEngine.GUI
             }
         }
 
+        private static void ProcessAlign(ref ParsingContext context, ref HtmlTag tag)
+        {
+            if (tag.IsSlash)
+            {
+                context.StyleStack.Pop();
+            }
+            else
+            {
+                var style = context.StyleStack.Peek();
+                if (tag.Attributes.TryGetValue(string.Empty, out var valign))
+                {
+                    style.Alignment &= ~TextBlockStyle.Alignments.VerticalMask;
+                    switch (valign)
+                    {
+                    case "left":
+                        style.Alignment = TextBlockStyle.Alignments.Left;
+                        break;
+                    case "right":
+                        style.Alignment = TextBlockStyle.Alignments.Right;
+                        break;
+                    case "center":
+                        style.Alignment = TextBlockStyle.Alignments.Center;
+                        break;
+                    }
+                }
+                context.StyleStack.Push(style);
+            }
+        }
+
+        private static void ProcessCenter(ref ParsingContext context, ref HtmlTag tag)
+        {
+            if (tag.IsSlash)
+            {
+                context.StyleStack.Pop();
+            }
+            else
+            {
+                var style = context.StyleStack.Peek();
+                style.Alignment = TextBlockStyle.Alignments.Center;
+                context.StyleStack.Push(style);
+            }
+        }
+
         private static Asset FindAsset(string name, System.Type type)
         {
             var ids = Content.GetAllAssetsByType(type);

Source/Engine/UI/GUI/Common/RichTextBox.cs

@@ -50,5 +50,14 @@ namespace FlaxEngine.GUI
                 BackgroundSelectedBrush = new SolidColorBrush(style.BackgroundSelected),
             };
         }
+
+        /// <inheritdoc />
+        protected override void OnSizeChanged()
+        {
+            base.OnSizeChanged();
+
+            // Refresh textblocks since thos emight depend on control size (eg. align right)
+            UpdateTextBlocks();
+        }
     }
 }

Source/Engine/UI/GUI/TextBlockStyle.cs

@@ -32,11 +32,32 @@ namespace FlaxEngine.GUI
             /// </summary>
             Bottom = 4,
 
+            /// <summary>
+            /// Block will be aligned to the left edge of the layout (horizontally).
+            /// </summary>
+            Left = 8,
+            
+            /// <summary>
+            /// Block will be aligned to center of the layout (horizontally).
+            /// </summary>
+            Center = 16,
+            
+            /// <summary>
+            /// Block will be aligned to the right edge of the layout (horizontally).
+            /// </summary>
+            Right = 32,
+
             /// <summary>
             /// Mask with vertical alignment flags.
             /// </summary>
             [HideInEditor]
             VerticalMask = Top | Middle | Bottom,
+
+            /// <summary>
+            /// Mask with horizontal alignment flags.
+            /// </summary>
+            [HideInEditor]
+            HorizontalMask = Left | Center | Right,
         }
 
         /// <summary>