feat: add underline and strikethrough decoration options

AGENTS.md

@@ -39,4 +39,4 @@ On Linux (or with `SHINYPDF_DEVCONTAINER=true`) the Linux native assets are adde
 
 ## Current focus
 
-Open issues: more underline options (#11), template designer app (#12). Markdown follow-ups not yet built: tables, images, task lists.
+Open issues: template designer app (#12). Markdown follow-ups not yet built: tables, images, task lists.

docs/reference/text.md

@@ -198,6 +198,9 @@ container.Column(column =>
 | Italic | `Italic(bool value = true)` | same |
 | Underline | `Underline(bool value = true)` | same |
 | Strikethrough | `Strikethrough(bool value = true)` | same |
+| Decoration line | `DecorationColor(string)`, `DecorationThickness(float)`, `DecorationSolid()`, `DecorationDouble()`, `DecorationDotted()`, `DecorationDashed()`, `DecorationWavy()` | same |
+| Underline position | `UnderlinePositionAuto()`, `UnderlineAtBaseline()`, `UnderlineBelowGlyphs()` | same |
+| Strikethrough position | `StrikethroughThroughGlyphs()`, `StrikethroughAtBaseline()` | same |
 | Position | `NormalPosition()`, `Subscript()`, `Superscript()` | same |
 | Wrapping | `WrapAnywhere(bool value = true)` | same |
 | Direction | `DirectionAuto()`, `DirectionFromLeftToRight()`, `DirectionFromRightToLeft()` | same |
@@ -255,12 +258,6 @@ container.Text(text =>
 
 `Italic()`, `Underline()` and `Strikethrough()` accept an optional `bool`, so you can switch an inherited decoration off, for example `Underline(false)`.
 
-Decoration lines use the text color and the position and thickness defined by the font. There are no options for line color, thickness or style. Current behavior with sub- and superscript:
-
-- Superscript: the underline is drawn at the position of normal-sized text, so it lines up with the surrounding text.
-- Subscript: the underline follows the lowered, smaller glyphs.
-- Strikethrough follows the glyphs; its thickness is scaled to 62.5% for sub- and superscript.
-
 ```csharp
 container.Text(text =>
 {
@@ -272,6 +269,65 @@ container.Text(text =>
 });
 ```
 
+#### Decoration line color, thickness and style
+
+By default, decoration lines use the text color, the thickness defined by the font, and a solid stroke. These settings apply to both underline and strikethrough:
+
+- `DecorationColor(string value)`: line color, independent of the text color. Same color formats and validation as `FontColor`.
+- `DecorationThickness(float value)`: line thickness in points. Values `<= 0` throw `ArgumentException`. For `DecorationDouble()` it is the thickness of each of the two lines.
+- `DecorationSolid()` (default), `DecorationDouble()`, `DecorationDotted()`, `DecorationDashed()`, `DecorationWavy()`: line style. Dots, dashes and waves scale with the thickness.
+
+```csharp
+container.Text(text =>
+{
+    text.Span("spelling mistake").Underline().DecorationWavy().DecorationColor(Colors.Red.Medium);
+    text.Span(" and ");
+    text.Span("removed").Strikethrough().DecorationDouble().DecorationThickness(0.75f);
+});
+```
+
+#### Underline position with sub- and superscript
+
+The underline position decides where underlines of sub- and superscript spans are drawn. Normal text is not affected.
+
+| Method | Superscript | Subscript |
+|---|---|---|
+| `UnderlinePositionAuto()` (default) | at the position of normal-sized text, in line with the surrounding text | follows the lowered, smaller glyphs |
+| `UnderlineAtBaseline()` | at the position of normal-sized text | at the position of normal-sized text |
+| `UnderlineBelowGlyphs()` | directly below the raised glyphs | follows the lowered, smaller glyphs |
+
+Use `UnderlineAtBaseline()` for a continuous underline across formulas like `H₂O`.
+
+```csharp
+container.Text(text =>
+{
+    text.DefaultTextStyle(x => x.Underline().UnderlineAtBaseline());
+    text.Span("H");
+    text.Span("2").Subscript();
+    text.Span("O");
+});
+```
+
+#### Strikethrough position with sub- and superscript
+
+The strikethrough position decides where strikethroughs of sub- and superscript spans are drawn. Normal text is not affected.
+
+| Method | Sub- and superscript |
+|---|---|
+| `StrikethroughThroughGlyphs()` (default) | through the shifted, smaller glyphs; unless `DecorationThickness` is set, the thickness is scaled to 62.5% |
+| `StrikethroughAtBaseline()` | at the position and thickness of normal-sized text, in line with the surrounding text |
+
+Use `StrikethroughAtBaseline()` for a single continuous line across formulas like `E=mc²`.
+
+```csharp
+container.Text(text =>
+{
+    text.DefaultTextStyle(x => x.Strikethrough().StrikethroughAtBaseline());
+    text.Span("E=mc");
+    text.Span("2").Superscript();
+});
+```
+
 ### Subscript and superscript
 
 `Subscript()` and `Superscript()` render the span at 62.5% of the font size, shifted down by 10% or up by 35% of the font size. To keep strokes visually as thick as the surrounding text, the font is matched one weight step heavier (+100). `NormalPosition()` resets an inherited position.
@@ -396,6 +452,8 @@ Values used when nothing else sets a property (`TextStyle.LibraryDefault`, inter
 | Weight | Normal (400) |
 | Position | Normal |
 | Italic, underline, strikethrough, wrap anywhere | off |
+| Decoration line | text color, font thickness, solid |
+| Underline position | Auto |
 | Direction | Auto |
 | Fallback | `Noto Color Emoji` (embedded), black |
 

src/ShinyPDF.Examples/TextExamples.cs

@@ -344,6 +344,125 @@ public void SuperscriptSubscript_Effects()
                });
         }
 
+        [Test]
+        public void SuperscriptSubscript_UnderlinePosition()
+        {
+            RenderingTest
+               .Create()
+               .PageSize(800, 300)
+               .ProduceImages()
+               .ShowResults()
+               .Render(container =>
+               {
+                   container
+                        .Padding(25)
+                        .DefaultTextStyle(x => x.FontSize(30).Underline())
+                        .Column(column =>
+                        {
+                            column.Spacing(25);
+
+                            column.Item().Text(text =>
+                            {
+                                text.Span("Auto: E = mc");
+                                text.Span("2").Superscript();
+                                text.Span(", H");
+                                text.Span("2").Subscript();
+                                text.Span("O");
+                            });
+
+                            column.Item().Text(text =>
+                            {
+                                text.DefaultTextStyle(x => x.UnderlineAtBaseline());
+
+                                text.Span("Baseline: E = mc");
+                                text.Span("2").Superscript();
+                                text.Span(", H");
+                                text.Span("2").Subscript();
+                                text.Span("O");
+                            });
+
+                            column.Item().Text(text =>
+                            {
+                                text.DefaultTextStyle(x => x.UnderlineBelowGlyphs());
+
+                                text.Span("Below glyphs: E = mc");
+                                text.Span("2").Superscript();
+                                text.Span(", H");
+                                text.Span("2").Subscript();
+                                text.Span("O");
+                            });
+                        });
+               });
+        }
+
+        [Test]
+        public void SuperscriptSubscript_StrikethroughPosition()
+        {
+            RenderingTest
+               .Create()
+               .PageSize(800, 200)
+               .ProduceImages()
+               .ShowResults()
+               .Render(container =>
+               {
+                   container
+                        .Padding(25)
+                        .DefaultTextStyle(x => x.FontSize(30).Strikethrough())
+                        .Column(column =>
+                        {
+                            column.Spacing(25);
+
+                            column.Item().Text(text =>
+                            {
+                                text.Span("Through glyphs: (E = mc");
+                                text.Span("2").Superscript();
+                                text.Span("), H");
+                                text.Span("2").Subscript();
+                                text.Span("O");
+                            });
+
+                            column.Item().Text(text =>
+                            {
+                                text.DefaultTextStyle(x => x.StrikethroughAtBaseline());
+
+                                text.Span("Baseline: (E = mc");
+                                text.Span("2").Superscript();
+                                text.Span("), H");
+                                text.Span("2").Subscript();
+                                text.Span("O");
+                            });
+                        });
+               });
+        }
+
+        [Test]
+        public void DecorationStyles()
+        {
+            RenderingTest
+               .Create()
+               .PageSize(600, 420)
+               .ProduceImages()
+               .ShowResults()
+               .Render(container =>
+               {
+                   container
+                        .Padding(25)
+                        .DefaultTextStyle(x => x.FontSize(24))
+                        .Column(column =>
+                        {
+                            column.Spacing(15);
+
+                            column.Item().Text("Solid underline").Underline();
+                            column.Item().Text("Double underline").Underline().DecorationDouble();
+                            column.Item().Text("Dotted underline").Underline().DecorationDotted();
+                            column.Item().Text("Dashed underline").Underline().DecorationDashed();
+                            column.Item().Text("Wavy red underline").Underline().DecorationWavy().DecorationColor(Colors.Red.Medium);
+                            column.Item().Text("Thick blue underline").Underline().DecorationThickness(3).DecorationColor(Colors.Blue.Medium);
+                            column.Item().Text("Dashed strikethrough").Strikethrough().DecorationDashed();
+                        });
+               });
+        }
+
         [Test]
         public void ParagraphSpacing()
         {

src/ShinyPDF.UnitTests/TestEngine/MockCanvas.cs

@@ -18,6 +18,7 @@ internal class MockCanvas : ICanvas
         public void Scale(float scaleX, float scaleY) => ScaleFunc(scaleX, scaleY);
 
         public void DrawRectangle(Position vector, Size size, string color) => DrawRectFunc(vector, size, color);
+        public void DrawTextDecoration(Position vector, float width, float thickness, string color, TextDecorationStyle style) => throw new NotImplementedException();
         public void DrawText(SKTextBlob skTextBlob, Position position, TextStyle style) => throw new NotImplementedException();
         public void DrawImage(SKImage image, Position position, Size size) => DrawImageFunc(image, position, size);
 

src/ShinyPDF.UnitTests/TestEngine/OperationRecordingCanvas.cs

@@ -16,6 +16,7 @@ internal class OperationRecordingCanvas : ICanvas
         public void Scale(float scaleX, float scaleY) => Operations.Add(new CanvasScaleOperation(scaleX, scaleY));
 
         public void DrawRectangle(Position vector, Size size, string color) => Operations.Add(new CanvasDrawRectangleOperation(vector, size, color));
+        public void DrawTextDecoration(Position vector, float width, float thickness, string color, TextDecorationStyle style) => throw new NotImplementedException();
         public void DrawText(SKTextBlob skTextBlob, Position position, TextStyle style) => throw new NotImplementedException();
         public void DrawImage(SKImage image, Position position, Size size) => Operations.Add(new CanvasDrawImageOperation(position, size));