AvalonEdit: Use indentation from first line on all following lines when word-wrapping.

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/NewLineElementGenerator.cs

@@ -77,6 +77,11 @@ namespace ICSharpCode.AvalonEdit.Rendering
 				}
 			}
 			
+			public override bool IsWhitespace(int visualColumn)
+			{
+				return true;
+			}
+			
 			public override bool HandlesLineBorders {
 				get { return true; }
 			}

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/SingleCharacterElementGenerator.cs

@@ -118,6 +118,11 @@ namespace ICSharpCode.AvalonEdit.Rendering
 				else
 					return -1;
 			}
+			
+			public override bool IsWhitespace(int visualColumn)
+			{
+				return true;
+			}
 		}
 		
 		sealed class TabTextElement : VisualLineElement
@@ -148,6 +153,11 @@ namespace ICSharpCode.AvalonEdit.Rendering
 				else
 					return -1;
 			}
+			
+			public override bool IsWhitespace(int visualColumn)
+			{
+				return true;
+			}
 		}
 		
 		sealed class TabGlyphRun : TextEmbeddedObject

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/TextView.cs

@@ -544,7 +544,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			VisualLine l = GetVisualLine(documentLine.LineNumber);
 			if (l == null) {
 				TextRunProperties globalTextRunProperties = CreateGlobalTextRunProperties();
-				TextParagraphProperties paragraphProperties = CreateParagraphProperties(globalTextRunProperties);
+				VisualLineTextParagraphProperties paragraphProperties = CreateParagraphProperties(globalTextRunProperties);
 				
 				while (heightTree.GetIsCollapsed(documentLine)) {
 					documentLine = documentLine.PreviousLine;
@@ -710,7 +710,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		double CreateAndMeasureVisualLines(Size availableSize)
 		{
 			TextRunProperties globalTextRunProperties = CreateGlobalTextRunProperties();
-			TextParagraphProperties paragraphProperties = CreateParagraphProperties(globalTextRunProperties);
+			VisualLineTextParagraphProperties paragraphProperties = CreateParagraphProperties(globalTextRunProperties);
 			
 			Debug.WriteLine("Measure availableSize=" + availableSize + ", scrollOffset=" + scrollOffset);
 			var firstLineInView = heightTree.GetLineByVisualPosition(scrollOffset.Y);
@@ -786,7 +786,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			};
 		}
 		
-		TextParagraphProperties CreateParagraphProperties(TextRunProperties defaultTextRunProperties)
+		VisualLineTextParagraphProperties CreateParagraphProperties(TextRunProperties defaultTextRunProperties)
 		{
 			return new VisualLineTextParagraphProperties {
 				defaultTextRunProperties = defaultTextRunProperties,
@@ -797,7 +797,7 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		
 		VisualLine BuildVisualLine(DocumentLine documentLine,
 		                           TextRunProperties globalTextRunProperties,
-		                           TextParagraphProperties paragraphProperties,
+		                           VisualLineTextParagraphProperties paragraphProperties,
 		                           VisualLineElementGenerator[] elementGeneratorsArray,
 		                           IVisualLineTransformer[] lineTransformersArray,
 		                           Size availableSize)
@@ -829,6 +829,8 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			int textOffset = 0;
 			TextLineBreak lastLineBreak = null;
 			var textLines = new List<TextLine>();
+			paragraphProperties.indent = 0;
+			paragraphProperties.firstLineInParagraph = true;
 			while (textOffset <= visualLine.VisualLength) {
 				TextLine textLine = formatter.FormatLine(
 					textSource,
@@ -840,12 +842,52 @@ namespace ICSharpCode.AvalonEdit.Rendering
 				textLines.Add(textLine);
 				textOffset += textLine.Length;
 				
+				// exit loop so that we don't do the indentation calculation if there's only a single line
+				if (textOffset >= visualLine.VisualLength)
+					break;
+				
+				if (paragraphProperties.firstLineInParagraph) {
+					paragraphProperties.firstLineInParagraph = false;
+					
+					TextEditorOptions options = this.Options;
+					double indentation = 0;
+					if (options.InheritWordWrapIndentation) {
+						// determine indentation for next line:
+						int indentVisualColumn = GetIndentationVisualColumn(visualLine);
+						if (indentVisualColumn > 0 && indentVisualColumn < textOffset) {
+							indentation = textLine.GetDistanceFromCharacterHit(new CharacterHit(indentVisualColumn, 0));
+						}
+					}
+					indentation += options.WordWrapIndentation;
+					// apply the calculated indentation unless it's more than half of the text editor size:
+					if (indentation > 0 && indentation * 2 < availableSize.Width)
+						paragraphProperties.indent = indentation;
+				}
 				lastLineBreak = textLine.GetTextLineBreak();
 			}
 			visualLine.SetTextLines(textLines);
 			heightTree.SetHeight(visualLine.FirstDocumentLine, visualLine.Height);
 			return visualLine;
 		}
+		
+		static int GetIndentationVisualColumn(VisualLine visualLine)
+		{
+			if (visualLine.Elements.Count == 0)
+				return 0;
+			int column = 0;
+			int elementIndex = 0;
+			VisualLineElement element = visualLine.Elements[elementIndex];
+			while (element.IsWhitespace(column)) {
+				column++;
+				if (column == element.VisualColumn + element.VisualLength) {
+					elementIndex++;
+					if (elementIndex == visualLine.Elements.Count)
+						break;
+					element = visualLine.Elements[elementIndex];
+				}
+			}
+			return column;
+		}
 		#endregion
 		
 		#region Arrange

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/VisualLineElement.cs

@@ -200,6 +200,14 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			return -1;
 		}
 		
+		/// <summary>
+		/// Gets whether the specified offset in this element is considered whitespace.
+		/// </summary>
+		public virtual bool IsWhitespace(int visualColumn)
+		{
+			return false;
+		}
+		
 		/// <summary>
 		/// Gets whether the <see cref="GetNextCaretPosition"/> implementation handles line borders.
 		/// If this property returns false, the caller of GetNextCaretPosition should handle the line

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/VisualLineText.cs

@@ -57,6 +57,13 @@ namespace ICSharpCode.AvalonEdit.Rendering
 			return new TextCharacters(text, 0, text.Length, this.TextRunProperties);
 		}
 		
+		/// <inheritdoc/>
+		public override bool IsWhitespace(int visualColumn)
+		{
+			int offset = visualColumn - this.VisualColumn + parentVisualLine.FirstDocumentLine.Offset + this.RelativeTextOffset;
+			return char.IsWhiteSpace(parentVisualLine.Document.GetCharAt(offset));
+		}
+		
 		/// <inheritdoc/>
 		public override TextSpan<CultureSpecificCharacterBufferRange> GetPrecedingText(int visualColumnLimit, ITextRunConstructionContext context)
 		{

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/Rendering/VisualLineTextParagraphProperties.cs

@@ -7,11 +7,13 @@ using System.Windows.Media.TextFormatting;
 
 namespace ICSharpCode.AvalonEdit.Rendering
 {
-	class VisualLineTextParagraphProperties : TextParagraphProperties
+	sealed class VisualLineTextParagraphProperties : TextParagraphProperties
 	{
 		internal TextRunProperties defaultTextRunProperties;
 		internal TextWrapping textWrapping;
 		internal double tabSize;
+		internal double indent;
+		internal bool firstLineInParagraph;
 		
 		public override double DefaultIncrementalTab {
 			get { return tabSize; }
@@ -20,10 +22,10 @@ namespace ICSharpCode.AvalonEdit.Rendering
 		public override FlowDirection FlowDirection { get { return FlowDirection.LeftToRight; } }
 		public override TextAlignment TextAlignment { get { return TextAlignment.Left; } }
 		public override double LineHeight { get { return double.NaN; } }
-		public override bool FirstLineInParagraph { get { return false; } }
+		public override bool FirstLineInParagraph { get { return firstLineInParagraph; } }
 		public override TextRunProperties DefaultTextRunProperties { get { return defaultTextRunProperties; } }
 		public override TextWrapping TextWrapping { get { return textWrapping; } }
 		public override TextMarkerProperties TextMarkerProperties { get { return null; } }
-		public override double Indent { get { return 0; } }
+		public override double Indent { get { return indent; } }
 	}
 }

src/Libraries/AvalonEdit/ICSharpCode.AvalonEdit/TextEditorOptions.cs

@@ -267,5 +267,42 @@ namespace ICSharpCode.AvalonEdit
 				}
 			}
 		}
+		
+		double wordWrapIndentation = 100;
+		
+		/// <summary>
+		/// Gets/Sets the indentation used for all lines except the first when word-wrapping.
+		/// The default value is 0.
+		/// </summary>
+		[DefaultValue(100)]
+		public virtual double WordWrapIndentation {
+			get { return wordWrapIndentation; }
+			set {
+				if (double.IsNaN(value) || double.IsInfinity(value))
+					throw new ArgumentOutOfRangeException("value", value, "value must not be NaN/infinity");
+				if (value != wordWrapIndentation) {
+					wordWrapIndentation = value;
+					OnPropertyChanged("WordWrapIndentation");
+				}
+			}
+		}
+		
+		bool inheritWordWrapIndentation = true;
+		
+		/// <summary>
+		/// Gets/Sets whether the indentation is inherited from the first line when word-wrapping.
+		/// The default value is true.
+		/// </summary>
+		/// <remarks>When combined with <see cref="WordWrapIndentation"/>, the inherited indentation is added to the word wrap indentation.</remarks>
+		[DefaultValue(true)]
+		public virtual bool InheritWordWrapIndentation {
+			get { return inheritWordWrapIndentation; }
+			set {
+				if (value != inheritWordWrapIndentation) {
+					inheritWordWrapIndentation = value;
+					OnPropertyChanged("InheritWordWrapIndentation");
+				}
+			}
+		}
 	}
 }