Features/support overprinting

Directory.Build.targets

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Update="SixLabors.ImageSharp" Version="3.0.*" />
+    <PackageReference Update="SixLabors.ImageSharp" Version="3.1.*" />
   </ItemGroup>
 
   <!-- Disable auto imports/usings from ImageSharp -->

samples/Synercoding.FileFormats.Pdf.ConsoleTester/Program.cs

@@ -216,6 +216,10 @@ public static void Main(string[] args)
 
                     page.Content.AddShapes(trimBox, static (trim, context) =>
                     {
+                        context.SetExtendedGraphicsState(new ExtendedGraphicsState()
+                        {
+                            Overprint = true
+                        });
                         context.SetStroke(new SpotColor(new Separation(LowLevel.PdfName.Get("CutContour"), PredefinedColors.Magenta), 1));
                         context.Rectangle(trim);
                         context.Stroke();

src/Synercoding.FileFormats.Pdf/ExtendedGraphicsState.cs

@@ -0,0 +1,23 @@
+namespace Synercoding.FileFormats.Pdf;
+
+/// <summary>
+/// Class representing an ExtGState dictionary.
+/// </summary>
+public sealed record class ExtendedGraphicsState
+{
+    /// <summary>
+    /// A flag specifying whether to apply overprint.
+    /// There are two separate overprint parameters: one for stroking and one for all other painting operations.
+    /// Specifying an <see cref="Overprint"/> entry sets both parameters
+    /// unless there is also an <see cref="OverprintNonStroking"/> entry in the same graphics state parameter dictionary,
+    /// in which case the <see cref="Overprint"/> entry sets only the overprint parameter for stroking.
+    /// </summary>
+    public bool? Overprint { get; set; }
+
+    /// <summary>
+    /// A flag specifying whether to apply overprint for painting operations other than stroking.
+    /// If this entry is absent, the <see cref="Overprint"/> entry, if any, sets this parameter.
+    /// </summary>
+    public bool? OverprintNonStroking { get; set; }
+}
+

src/Synercoding.FileFormats.Pdf/GraphicState.cs → src/Synercoding.FileFormats.Pdf/GraphicsState.cs

@@ -7,9 +7,9 @@ namespace Synercoding.FileFormats.Pdf;
 /// <summary>
 /// Class representing the grahpic state of a PDF at a certain moment in time.
 /// </summary>
-public sealed class GraphicState
+public sealed class GraphicsState
 {
-    internal GraphicState()
+    internal GraphicsState()
     {
         CTM = Matrix.Identity;
         Fill = PredefinedColors.Black;
@@ -111,9 +111,9 @@ internal GraphicState()
     /// </summary>
     public double TextRise { get; internal set; }
 
-    internal GraphicState Clone()
+    internal GraphicsState Clone()
     {
-        return new GraphicState()
+        return new GraphicsState()
         {
             CTM = CTM,
             Fill = Fill,

src/Synercoding.FileFormats.Pdf/IContentContext.cs

@@ -19,7 +19,7 @@ public interface IContentContext<TSelf>
     /// <summary>
     /// Represents the current graphic state
     /// </summary>
-    GraphicState GraphicState { get; }
+    GraphicsState GraphicState { get; }
 
     /// <summary>
     /// Wrap the <paramref name="contentOperations"/> in save and restore state operators
@@ -40,7 +40,7 @@ public interface IContentContext<TSelf>
     Task<TSelf> WrapInStateAsync<T>(T data, Func<T, TSelf, Task> contentOperations);
 
     /// <summary>
-    /// Concatenate a matrix to <see cref="GraphicState.CTM"/>
+    /// Concatenate a matrix to <see cref="GraphicsState.CTM"/>
     /// </summary>
     /// <param name="matrix">The matrix to concat</param>
     /// <returns>This <see cref="IContentContext{TSelf}"/> to enable chaining operations</returns>
@@ -94,5 +94,12 @@ public interface IContentContext<TSelf>
     /// <param name="dashPattern">The dash pattern to set</param>
     /// <returns>This <see cref="IContentContext{TSelf}"/> to enable chaining operations</returns>
     TSelf SetDashPattern(Dash dashPattern);
+
+    /// <summary>
+    /// Set an extended graphics state (ExtGState) dictionary.
+    /// </summary>
+    /// <param name="extendedGraphicsState">The state to apply.</param>
+    /// <returns>This <see cref="IContentContext{TSelf}"/> to enable chaining operations</returns>
+    TSelf SetExtendedGraphicsState(ExtendedGraphicsState extendedGraphicsState);
 }
 

src/Synercoding.FileFormats.Pdf/ITextContentContext.cs

@@ -101,7 +101,7 @@ public interface ITextContentContext : IContentContext<ITextContentContext>
     ITextContentContext ShowTextOnNextLine(string text);
 
     /// <summary>
-    /// Operation to show text on the next line and setting the <see cref="GraphicState.WordSpacing"/> and <see cref="GraphicState.CharacterSpacing"/>
+    /// Operation to show text on the next line and setting the <see cref="GraphicsState.WordSpacing"/> and <see cref="GraphicsState.CharacterSpacing"/>
     /// </summary>
     /// <param name="text">The text to show</param>
     /// <param name="wordSpacing">The word spacing to set</param>

src/Synercoding.FileFormats.Pdf/Internals/PageContentContext.cs

@@ -6,15 +6,15 @@ namespace Synercoding.FileFormats.Pdf.Internals;
 
 internal class PageContentContext : IPageContentContext
 {
-    public PageContentContext(ContentStream contentStream, GraphicState graphicState)
+    public PageContentContext(ContentStream contentStream, GraphicsState graphicState)
     {
         RawContentStream = contentStream;
         GraphicState = graphicState;
     }
 
     public ContentStream RawContentStream { get; }
 
-    public GraphicState GraphicState { get; }
+    public GraphicsState GraphicState { get; }
 
     public IPageContentContext AddImage(Image image)
     {
@@ -155,4 +155,11 @@ public async Task<IPageContentContext> AddShapesAsync<T>(T data, Func<T, IShapeC
 
         return this;
     }
+
+    public IPageContentContext SetExtendedGraphicsState(ExtendedGraphicsState extendedGraphicsState)
+    {
+        RawContentStream.SetExtendedGraphicsState(extendedGraphicsState);
+
+        return this;
+    }
 }

src/Synercoding.FileFormats.Pdf/Internals/ShapesContentContext.cs

@@ -6,15 +6,15 @@ namespace Synercoding.FileFormats.Pdf.Internals;
 
 internal class ShapesContentContext : IShapeContentContext
 {
-    public ShapesContentContext(ContentStream contentStream, GraphicState graphicState)
+    public ShapesContentContext(ContentStream contentStream, GraphicsState graphicState)
     {
         RawContentStream = contentStream;
         GraphicState = graphicState;
     }
 
     public ContentStream RawContentStream { get; }
 
-    public GraphicState GraphicState { get; }
+    public GraphicsState GraphicState { get; }
 
     public IShapeContentContext ConcatenateMatrix(Matrix matrix)
     {
@@ -204,4 +204,11 @@ public IShapeContentContext EndPathNoStrokeNoFill()
 
         return this;
     }
+
+    public IShapeContentContext SetExtendedGraphicsState(ExtendedGraphicsState extendedGraphicsState)
+    {
+        RawContentStream.SetExtendedGraphicsState(extendedGraphicsState);
+
+        return this;
+    }
 }

src/Synercoding.FileFormats.Pdf/Internals/TextContentContext.cs

@@ -7,15 +7,15 @@ namespace Synercoding.FileFormats.Pdf.Internals;
 
 internal class TextContentContext : ITextContentContext
 {
-    public TextContentContext(ContentStream contentStream, GraphicState graphicState)
+    public TextContentContext(ContentStream contentStream, GraphicsState graphicState)
     {
         RawContentStream = contentStream;
         GraphicState = graphicState;
     }
 
     public ContentStream RawContentStream { get; }
 
-    public GraphicState GraphicState { get; }
+    public GraphicsState GraphicState { get; }
 
     public ITextContentContext ConcatenateMatrix(Matrix matrix)
     {
@@ -225,4 +225,11 @@ public ITextContentContext ShowTextOnNextLine(string text, double wordSpacing, d
 
         return this;
     }
+
+    public ITextContentContext SetExtendedGraphicsState(ExtendedGraphicsState extendedGraphicsState)
+    {
+        RawContentStream.SetExtendedGraphicsState(extendedGraphicsState);
+
+        return this;
+    }
 }

src/Synercoding.FileFormats.Pdf/LowLevel/ContentStream.cs

@@ -387,6 +387,20 @@ public ContentStream Paint(PdfName resource)
         return this;
     }
 
+    /// <summary>
+    /// Set an extended graphics state (ExtGState) dictionary using a gs operator..
+    /// </summary>
+    /// <param name="state">The state to apply.</param>
+    /// <returns>The <see cref="ContentStream"/> to support chaining operations.</returns>
+    public ContentStream SetExtendedGraphicsState(ExtendedGraphicsState state)
+    {
+        var name = Resources.AddExtendedGraphicsState(state);
+
+        InnerStream.Write(name).Space().Write("gs").NewLine();
+
+        return this;
+    }
+
     /// <summary>
     /// Write the operator (m) to the stream
     /// </summary>

src/Synercoding.FileFormats.Pdf/LowLevel/Graphics/LineJoinStyle.cs

@@ -9,7 +9,7 @@ public enum LineJoinStyle
     /// The outer edges of the strokes for the two segments shall be extended until they meet at an angle.
     /// </summary>
     /// <remarks>
-    /// If the segments meet at too sharp an angle (see <see cref="GraphicState.MiterLimit"/>), a bevel join shall be used instead.
+    /// If the segments meet at too sharp an angle (see <see cref="GraphicsState.MiterLimit"/>), a bevel join shall be used instead.
     /// </remarks>
     MiterJoin = 0,
     /// <summary>

src/Synercoding.FileFormats.Pdf/LowLevel/Internal/PageResources.cs

@@ -9,12 +9,15 @@ internal sealed class PageResources : IDisposable
 {
     private const string PREFIX_IMAGE = "Im";
     private const string PREFIX_SEPARATION = "Sep";
+    private const string PREFIX_EXTGSTATE = "ExGs";
 
     private readonly TableBuilder _tableBuilder;
     private readonly Map<PdfName, Image> _images;
     private readonly Dictionary<Separation, (PdfName Name, PdfReference Id)> _separations;
     private readonly Dictionary<Type1StandardFont, PdfReference> _standardFonts;
+    private readonly Dictionary<ExtendedGraphicsState, (PdfName Name, PdfReference Id)> _extendedGraphicsStates;
 
+    private int _stateCounter = 0;
     private int _separationCounter = 0;
     private int _imageCounter = 0;
 
@@ -24,11 +27,15 @@ internal PageResources(TableBuilder tableBuilder)
         _images = new Map<PdfName, Image>();
         _separations = new Dictionary<Separation, (PdfName Name, PdfReference Id)>();
         _standardFonts = new Dictionary<Type1StandardFont, PdfReference>();
+        _extendedGraphicsStates = new Dictionary<ExtendedGraphicsState, (PdfName Name, PdfReference Id)>();
     }
 
     public IReadOnlyDictionary<PdfName, Image> Images
         => _images.Forward;
 
+    public IReadOnlyDictionary<ExtendedGraphicsState, (PdfName Name, PdfReference Id)> ExtendedGraphicsStates
+        => _extendedGraphicsStates;
+
     internal IReadOnlyDictionary<Separation, (PdfName Name, PdfReference Id)> SeparationReferences
         => _separations;
 
@@ -105,4 +112,16 @@ internal PdfName AddSeparation(Separation separation)
 
         return name;
     }
+
+    internal PdfName AddExtendedGraphicsState(ExtendedGraphicsState extendedGraphicsState)
+    {
+        if (_extendedGraphicsStates.TryGetValue(extendedGraphicsState, out var tuple))
+            return tuple.Name;
+
+        var key = PREFIX_EXTGSTATE + Interlocked.Increment(ref _stateCounter).ToString().PadLeft(6, '0');
+        var name = PdfName.Get(key);
+        _extendedGraphicsStates[extendedGraphicsState] = (name, _tableBuilder.ReserveId());
+
+        return name;
+    }
 }

src/Synercoding.FileFormats.Pdf/LowLevel/ObjectStream.cs

@@ -159,6 +159,18 @@ public ObjectStream Write(PdfPage page)
                         }
                     }));
                 }
+
+                if (resources.ExtendedGraphicsStates.Count != 0)
+                {
+                    stream.Write(PdfName.Get("ExtGState"), resources.ExtendedGraphicsStates.Values, static (extGStates, stream) => stream.Dictionary(extGStates, static (extendedGStates, dict) =>
+                    {
+                        foreach (var (name, reference) in extendedGStates)
+                        {
+                            dict.Write(name, reference);
+                        }
+                    }));
+                }
+
             }));
 
             // Content stream
@@ -217,6 +229,22 @@ public ObjectStream Write(PdfReference reference, Separation separation)
         return this;
     }
 
+    public ObjectStream Write(PdfReference reference, ExtendedGraphicsState state)
+    {
+        if (!_tableBuilder.TrySetPosition(reference, InnerStream.Position))
+            return this;
+
+        _indirectDictionary(reference, state, static (state, dict) =>
+        {
+            if (state.Overprint.HasValue)
+                dict.Write(PdfName.Get("OP"), state.Overprint.Value);
+            if (state.OverprintNonStroking.HasValue)
+                dict.Write(PdfName.Get("op"), state.OverprintNonStroking.Value);
+        });
+
+        return this;
+    }
+
     private void _indirectDictionary<T>(PdfReference reference, T data, Action<T, PdfDictionary> dictionaryAction)
     {
         InnerStream

src/Synercoding.FileFormats.Pdf/LowLevel/PdfDictionary.cs

@@ -146,6 +146,22 @@ public PdfDictionary Write(PdfName key, int value)
         return this;
     }
 
+    /// <summary>
+    /// Write a boolean to the dictionary
+    /// </summary>
+    /// <param name="key">The key of the item in the dictionary</param>
+    /// <param name="value">The boolean to write</param>
+    /// <returns>The <see cref="PdfDictionary"/> to support chaining operations.</returns>
+    public PdfDictionary Write(PdfName key, bool value)
+    {
+        _stream
+            .Write(key)
+            .Space()
+            .Write(value);
+
+        return this;
+    }
+
     /// <summary>
     /// Write a text to the dictionary
     /// </summary>

src/Synercoding.FileFormats.Pdf/LowLevel/PdfStream.cs

@@ -56,6 +56,18 @@ public PdfStream Write(char c)
         return WriteByte((byte)( c & 0xFF ));
     }
 
+    /// <summary>
+    /// Write a <see cref="bool"/> to the stream
+    /// </summary>
+    /// <param name="b">The boolean to write.</param>
+    /// <returns>The calling <see cref="PdfStream"/> to support chaining operations.</returns>
+    public PdfStream Write(bool b)
+    {
+        return b
+            ? Write("true")
+            : Write("false");
+    }
+
     /// <summary>
     /// Write a <see cref="int"/> to the stream
     /// </summary>

src/Synercoding.FileFormats.Pdf/PdfPage.cs

@@ -26,7 +26,7 @@ internal PdfPage(TableBuilder tableBuilder, PageTree parent)
         Resources = new PageResources(_tableBuilder);
         var contentStream = new ContentStream(tableBuilder.ReserveId(), Resources);
 
-        Content = new PageContentContext(contentStream, new GraphicState());
+        Content = new PageContentContext(contentStream, new GraphicsState());
     }
 
     internal PdfReference Parent

src/Synercoding.FileFormats.Pdf/PdfWriter.cs

@@ -233,6 +233,9 @@ private void _writePageAndResourcesToObjectStream(PdfPage page)
         foreach (var (separation, (_, refId)) in page.Resources.SeparationReferences)
             _objectStream.Write(refId, separation);
 
+        foreach (var (state, (_, refId)) in page.Resources.ExtendedGraphicsStates)
+            _objectStream.Write(refId, state);
+
         _objectStream.Write(page.Content.RawContentStream);
     }