Add type PencilMarkViewNode (Closes #367).

src/Sudoku.Gdip/Gdip/DrawingConfigurations.cs

@@ -205,6 +205,11 @@ public sealed class DrawingConfigurations
 	/// </summary>
 	public Color WheelTextColor { get; set; } = Color.Black;
 
+	/// <summary>
+	/// Indicates pencilmark text color.
+	/// </summary>
+	public Color PencilmarkTextColor { get; set; } = Color.DimGray;
+
 	/// <summary>
 	/// The color palette. This property stores a list of customized colors to be used as user-defined colors.
 	/// </summary>
@@ -256,4 +261,9 @@ public sealed class DrawingConfigurations
 	/// Indicates the font of wheel text.
 	/// </summary>
 	public FontData WheelFont { get; set; } = new("MiSans", 12F, FontStyle.Regular);
+
+	/// <summary>
+	/// Indicates the font of pencilmarks.
+	/// </summary>
+	public FontData PencilmarkFont { get; set; } = new("Segoe UI", 12F, FontStyle.Regular);
 }

src/Sudoku.Gdip/Gdip/FontData.cs

@@ -45,4 +45,22 @@ public bool Equals([NotNullWhen(true)] FontData? other)
 
 	[GeneratedOverriddingMember(GeneratedGetHashCodeBehavior.CallingHashCodeCombine, nameof(FontName), nameof(FontSize), nameof(FontStyle))]
 	public override partial int GetHashCode();
+
+
+	/// <summary>
+	/// Creates a <see cref="Font"/> instance via the current <see cref="FontData"/> instance.
+	/// </summary>
+	/// <returns>
+	/// The <see cref="Font"/> instance created. Please note that the created result should use <see langword="using"/> statement
+	/// to limit the lifestyle:
+	/// <code><![CDATA[
+	/// using var font = data.CreateFont();
+	/// ]]></code>
+	/// </returns>
+	[MethodImpl(MethodImplOptions.AggressiveInlining)]
+	public Font CreateFont()
+	{
+		var (fontName, fontSize, fontStyle) = this;
+		return new(fontName, fontSize, fontStyle);
+	}
 }

src/Sudoku.Gdip/Gdip/IGridImageGenerator.cs

@@ -242,6 +242,7 @@ private static Font GetFont(string? fontName, float size, decimal scale, FontSty
 	partial void DrawClockfaceDot(Graphics g);
 	partial void DrawNeighborSigns(Graphics g);
 	partial void DrawWheel(Graphics g);
+	partial void DrawPencilmarks(Graphics g);
 }
 
 partial class GridImageGenerator
@@ -359,7 +360,6 @@ partial void DrawView(Graphics g)
 		DrawLinks(g);
 		DrawUnknownValue(g);
 
-#if ENHANCED_DRAWING_APIS
 		// Shapes
 		DrawBorderBar(g);
 		DrawKropkiDot(g);
@@ -371,7 +371,7 @@ partial void DrawView(Graphics g)
 		DrawClockfaceDot(g);
 		DrawNeighborSigns(g);
 		DrawWheel(g);
-#endif
+		DrawPencilmarks(g);
 	}
 
 	/// <summary>
@@ -1316,7 +1316,7 @@ partial void DrawWheel(Graphics g)
 		using var font = new Font(fontName, fontSize, fontStyle);
 		using var textBrush = new SolidBrush(textColor);
 
-		var positions = (stackalloc PointF[4]);
+		scoped var positions = (stackalloc PointF[4]);
 		foreach (var wheelNode in wheelNodes)
 		{
 			if (wheelNode is not (var cell, _) { Identifier: var identifier, DigitString: var digitString })
@@ -1335,9 +1335,9 @@ partial void DrawWheel(Graphics g)
 			g.DrawEllipse(pen, rect);
 
 			// Draw strings.
-			positions[0] = new(x, y - ch * SqrtOf2 / 2/* - fontSize / 4*/); // fontSize / 4: a little offset correction.
+			positions[0] = new(x, y - ch * SqrtOf2 / 2);
 			positions[1] = new(x + ch * SqrtOf2 / 2, y);
-			positions[2] = new(x, y + ch * SqrtOf2 / 2/* + fontSize / 4*/);
+			positions[2] = new(x, y + ch * SqrtOf2 / 2);
 			positions[3] = new(x - ch * SqrtOf2 / 2, y);
 			for (var i = 0; i < 4; i++)
 			{
@@ -1352,4 +1352,41 @@ partial void DrawWheel(Graphics g)
 			}
 		}
 	}
+
+	/// <summary>
+	/// Draw pencilmarks.
+	/// </summary>
+	/// <param name="g"><inheritdoc cref="RenderTo(Graphics)" path="/param[@name='g']"/></param>
+	[Conditional("ENHANCED_DRAWING_APIS")]
+	partial void DrawPencilmarks(Graphics g)
+	{
+		if (this is not
+			{
+				View.PencilMarkNodes: var pencilmarkNodes,
+				Calculator: { CellSize: var (_, ch) } calc,
+				Preferences: { PencilmarkFont: var fontData, PencilmarkTextColor: var textColor }
+			})
+		{
+			return;
+		}
+
+		using var font = fontData.CreateFont();
+		using var textBrush = new SolidBrush(textColor);
+
+		foreach (var pencilmarkNode in pencilmarkNodes)
+		{
+			if (pencilmarkNode is not (var cell, _) { Notation: var notation })
+			{
+				continue;
+			}
+
+			var renderingSize = g.MeasureString(notation, font);
+			var (_, th) = renderingSize;
+			var (centerX, centerY) = calc.GetMousePointInCenter(cell);
+			var position = new PointF(centerX, centerY - ch / 2 + th / 2);
+
+			// Draw text.
+			g.DrawString(notation, font, textBrush, position, DefaultStringFormat);
+		}
+	}
 }

src/Sudoku.Presentation/Presentation/Nodes/Shapes/PencilMarkViewNode.cs

@@ -0,0 +1,38 @@
+namespace Sudoku.Presentation.Nodes.Shapes;
+
+/// <summary>
+/// Defines a pencil-mark view node.
+/// </summary>
+public sealed partial class PencilMarkViewNode : SingleCellMarkViewNode
+{
+	/// <summary>
+	/// Initializes a <see cref="PencilMarkViewNode"/> instance via the specified values.
+	/// </summary>
+	/// <param name="cell">The cell.</param>
+	/// <param name="notation">The notation.</param>
+	[MethodImpl(MethodImplOptions.AggressiveInlining)]
+	public PencilMarkViewNode(int cell, string notation) : base(DisplayColorKind.Normal, cell, Direction.None) => Notation = notation;
+
+
+	/// <summary>
+	/// Indicates the notation.
+	/// </summary>
+	public string Notation { get; }
+
+
+	/// <inheritdoc/>
+	[MethodImpl(MethodImplOptions.AggressiveInlining)]
+	public override bool Equals([NotNullWhen(true)] ViewNode? other)
+		=> other is PencilMarkViewNode comparer
+		&& Identifier == comparer.Identifier && Cell == comparer.Cell && Notation == comparer.Notation;
+
+	[GeneratedOverriddingMember(GeneratedGetHashCodeBehavior.CallingHashCodeCombine, nameof(Identifier), nameof(Cell), nameof(Notation))]
+	public override partial int GetHashCode();
+
+	[GeneratedOverriddingMember(GeneratedToStringBehavior.RecordLike, nameof(Identifier), nameof(Cell), nameof(Notation))]
+	public override partial string ToString();
+
+	/// <inheritdoc/>
+	[MethodImpl(MethodImplOptions.AggressiveInlining)]
+	public override PencilMarkViewNode Clone() => new(Cell, Notation);
+}

src/Sudoku.Presentation/Presentation/View.cs

@@ -107,6 +107,11 @@ private View()
 	/// </summary>
 	public IEnumerable<WheelViewNode> WheelNodes => _nodes.OfType<WheelViewNode>();
 
+	/// <summary>
+	/// Indicates pencilmark nodes that the current data type stores.
+	/// </summary>
+	public IEnumerable<PencilMarkViewNode> PencilMarkNodes => _nodes.OfType<PencilMarkViewNode>();
+
 
 	/// <summary>
 	/// Indicates the empty instance.