Allow to have multiple content stream in a page

You can create new content stream (NewContentStreamAfter, NewContentStreamBefore) and select (SelectContentStream) which one we are editing at the moment

src/UglyToad.PdfPig.Tests/Writer/PdfDocumentBuilderTests.cs

@@ -136,7 +136,7 @@
 
             var letters = page.AddText("Hello World!", 12, new PdfPoint(30, 50), font);
 
-            Assert.NotEmpty(page.Operations);
+            Assert.NotEmpty(page.CurrentStream.Operations);
 
             var b = builder.Build();
 
@@ -186,7 +186,7 @@
 
             page.AddText("eé", 12, new PdfPoint(30, 520), font);
 
-            Assert.NotEmpty(page.Operations);
+            Assert.NotEmpty(page.CurrentStream.Operations);
 
             var b = builder.Build();
 
@@ -232,7 +232,7 @@
 
             page.AddText("eé", 12, new PdfPoint(30, 520), font);
 
-            Assert.NotEmpty(page.Operations);
+            Assert.NotEmpty(page.CurrentStream.Operations);
 
             var b = builder.Build();
 
@@ -279,7 +279,7 @@
             var letters = page.AddText("Hello World!", 16, new PdfPoint(30, 520), font);
             page.AddText("This is some further text continuing to write", 12, new PdfPoint(30, 500), font);
 
-            Assert.NotEmpty(page.Operations);
+            Assert.NotEmpty(page.CurrentStream.Operations);
 
             var b = builder.Build();
 
@@ -603,6 +603,47 @@
             WriteFile(nameof(CanCreateDocumentWithFilledRectangle), file);
         }
 
+        [Fact]
+        public void CanGeneratePageWithMultipleStream()
+        {
+            var builder = new PdfDocumentBuilder();
+
+            var page = builder.AddPage(PageSize.A4);
+
+            var file = TrueTypeTestHelper.GetFileBytes("Andada-Regular.ttf");
+
+            var font = builder.AddTrueTypeFont(file);
+
+            var letters = page.AddText("Hello", 12, new PdfPoint(30, 50), font);
+
+            Assert.NotEmpty(page.CurrentStream.Operations);
+
+            page.NewContentStreamAfter();
+
+            page.AddText("World!", 12, new PdfPoint(50, 50), font);
+
+            Assert.NotEmpty(page.CurrentStream.Operations);
+
+
+            var b = builder.Build();
+
+            WriteFile(nameof(CanGeneratePageWithMultipleStream), b);
+
+            Assert.NotEmpty(b);
+
+            using (var document = PdfDocument.Open(b))
+            {
+                var page1 = document.GetPage(1);
+
+                Assert.Equal("HelloWorld!", page1.Text);
+
+                var h = page1.Letters[0];
+
+                Assert.Equal("H", h.Value);
+                Assert.Equal("Andada-Regular", h.FontName);
+            }
+        }
+
         private static void WriteFile(string name, byte[] bytes, string extension = "pdf")
         {
             try

src/UglyToad.PdfPig/Writer/PdfDocumentBuilder.cs

@@ -308,14 +308,27 @@ namespace UglyToad.PdfPig.Writer
 
                     pageDictionary[NameToken.Resources] = new DictionaryToken(individualResources);
 
-                    if (page.Value.Operations.Count > 0)
+                    if (page.Value.ContentStreams.Count == 1)
                     {
-                        var contentStream = WriteContentStream(page.Value.Operations);
+                        var contentStream = WriteContentStream(page.Value.CurrentStream.Operations);
 
                         var contentStreamObj = context.WriteObject(memory, contentStream);
 
                         pageDictionary[NameToken.Contents] = new IndirectReferenceToken(contentStreamObj.Number);
                     }
+                    else if (page.Value.ContentStreams.Count > 1)
+                    {
+                        var streamTokens = page.Value.ContentStreams.Select(contentStream =>
+                        {
+                            var streamToken = WriteContentStream(contentStream.Operations);
+
+                            var contentStreamObj = context.WriteObject(memory, streamToken);
+
+                            return new IndirectReferenceToken(contentStreamObj.Number);
+                        }).ToList();
+
+                        pageDictionary[NameToken.Contents] = new ArrayToken(streamTokens);
+                    }
 
                     var pageRef = context.WriteObject(memory, new DictionaryToken(pageDictionary));
 

src/UglyToad.PdfPig/Writer/PdfPageBuilder.cs

@@ -27,7 +27,7 @@
     public class PdfPageBuilder
     {
         private readonly PdfDocumentBuilder documentBuilder;
-        private readonly List<IGraphicsStateOperation> operations = new List<IGraphicsStateOperation>();
+        private readonly List<ContentStream> contentStreams;
         private readonly Dictionary<NameToken, IToken> resourcesDictionary = new Dictionary<NameToken, IToken>();
 
         //a sequence number of ShowText operation to determine whether letters belong to same operation or not (letters that belong to different operations have less changes to belong to same word)
@@ -35,8 +35,6 @@
 
         private int imageKey = 1;
 
-        internal IReadOnlyList<IGraphicsStateOperation> Operations => operations;
-
         internal IReadOnlyDictionary<NameToken, IToken> Resources => resourcesDictionary;
 
         /// <summary>
@@ -52,13 +50,59 @@
         /// <summary>
         /// Access to the underlying data structures for advanced use cases.
         /// </summary>
-        public AdvancedEditing Advanced { get; }
+        public ContentStream CurrentStream { get; private set; }
+
+        /// <summary>
+        /// Access to
+        /// </summary>
+        public IReadOnlyList<ContentStream> ContentStreams { get; }
 
         internal PdfPageBuilder(int number, PdfDocumentBuilder documentBuilder)
         {
             this.documentBuilder = documentBuilder ?? throw new ArgumentNullException(nameof(documentBuilder));
             PageNumber = number;
-            Advanced = new AdvancedEditing(operations);
+
+            CurrentStream = new ContentStream();
+            ContentStreams = contentStreams = new List<ContentStream>()
+            {
+                CurrentStream
+            };
+        }
+
+        /// <summary>
+        /// Allow to append a new content stream before the current one and select it
+        /// </summary>
+        public void NewContentStreamBefore()
+        {
+            var index = Math.Max(contentStreams.IndexOf(CurrentStream) - 1, 0);
+
+            CurrentStream = new ContentStream();
+            contentStreams.Insert(index, CurrentStream);
+        }
+
+        /// <summary>
+        /// Allow to append a new content stream after the current one and select it
+        /// </summary>
+        public void NewContentStreamAfter()
+        {
+            var index = Math.Min(contentStreams.IndexOf(CurrentStream) + 1, contentStreams.Count);
+
+            CurrentStream = new ContentStream();
+            contentStreams.Insert(index, CurrentStream);
+        }
+
+        /// <summary>
+        /// Select a content stream from the list, by his index
+        /// </summary>
+        /// <param name="index">index of the content stream to be selected</param>
+        public void SelectContentStream(int index)
+        {
+            if (index < 0 || index >= ContentStreams.Count)
+            {
+                throw new IndexOutOfRangeException(nameof(index));
+            }
+
+            CurrentStream = ContentStreams[index];
         }
 
         /// <summary>
@@ -71,16 +115,16 @@
         {
             if (lineWidth != 1)
             {
-                operations.Add(new SetLineWidth(lineWidth));
+                CurrentStream.Add(new SetLineWidth(lineWidth));
             }
 
-            operations.Add(new BeginNewSubpath((decimal)from.X, (decimal)from.Y));
-            operations.Add(new AppendStraightLineSegment((decimal)to.X, (decimal)to.Y));
-            operations.Add(StrokePath.Value);
+            CurrentStream.Add(new BeginNewSubpath((decimal)from.X, (decimal)from.Y));
+            CurrentStream.Add(new AppendStraightLineSegment((decimal)to.X, (decimal)to.Y));
+            CurrentStream.Add(StrokePath.Value);
 
             if (lineWidth != 1)
             {
-                operations.Add(new SetLineWidth(1));
+                CurrentStream.Add(new SetLineWidth(1));
             }
         }
 
@@ -96,23 +140,23 @@
         {
             if (lineWidth != 1)
             {
-                operations.Add(new SetLineWidth(lineWidth));
+                CurrentStream.Add(new SetLineWidth(lineWidth));
             }
 
-            operations.Add(new AppendRectangle((decimal)position.X, (decimal)position.Y, width, height));
+            CurrentStream.Add(new AppendRectangle((decimal)position.X, (decimal)position.Y, width, height));
 
             if (fill)
             {
-                operations.Add(FillPathEvenOddRuleAndStroke.Value);
+                CurrentStream.Add(FillPathEvenOddRuleAndStroke.Value);
             }
             else
             {
-                operations.Add(StrokePath.Value);
+                CurrentStream.Add(StrokePath.Value);
             }
 
             if (lineWidth != 1)
             {
-                operations.Add(new SetLineWidth(lineWidth));
+                CurrentStream.Add(new SetLineWidth(lineWidth));
             }
         }
 
@@ -124,8 +168,8 @@
         /// <param name="b">Blue - 0 to 255</param>
         public void SetStrokeColor(byte r, byte g, byte b)
         {
-            operations.Add(Push.Value);
-            operations.Add(new SetStrokeColorDeviceRgb(RgbToDecimal(r), RgbToDecimal(g), RgbToDecimal(b)));
+            CurrentStream.Add(Push.Value);
+            CurrentStream.Add(new SetStrokeColorDeviceRgb(RgbToDecimal(r), RgbToDecimal(g), RgbToDecimal(b)));
         }
 
         /// <summary>
@@ -136,8 +180,8 @@
         /// <param name="b">Blue - 0 to 1</param>
         internal void SetStrokeColorExact(decimal r, decimal g, decimal b)
         {
-            operations.Add(Push.Value);
-            operations.Add(new SetStrokeColorDeviceRgb(CheckRgbDecimal(r, nameof(r)),
+            CurrentStream.Add(Push.Value);
+            CurrentStream.Add(new SetStrokeColorDeviceRgb(CheckRgbDecimal(r, nameof(r)),
                 CheckRgbDecimal(g, nameof(g)), CheckRgbDecimal(b, nameof(b))));
         }
 
@@ -149,8 +193,8 @@
         /// <param name="b">Blue - 0 to 255</param>
         public void SetTextAndFillColor(byte r, byte g, byte b)
         {
-            operations.Add(Push.Value);
-            operations.Add(new SetNonStrokeColorDeviceRgb(RgbToDecimal(r), RgbToDecimal(g), RgbToDecimal(b)));
+            CurrentStream.Add(Push.Value);
+            CurrentStream.Add(new SetNonStrokeColorDeviceRgb(RgbToDecimal(r), RgbToDecimal(g), RgbToDecimal(b)));
         }
 
         /// <summary>
@@ -158,7 +202,7 @@
         /// </summary>
         public void ResetColor()
         {
-            operations.Add(Pop.Value);
+            CurrentStream.Add(Pop.Value);
         }
 
         /// <summary>
@@ -244,15 +288,15 @@
 
             var letters = DrawLetters(text, fontProgram, fm, fontSize, textMatrix);
 
-            operations.Add(BeginText.Value);
-            operations.Add(new SetFontAndSize(font.Name, fontSize));
-            operations.Add(new MoveToNextLineWithOffset((decimal)position.X, (decimal)position.Y));
+            CurrentStream.Add(BeginText.Value);
+            CurrentStream.Add(new SetFontAndSize(font.Name, fontSize));
+            CurrentStream.Add(new MoveToNextLineWithOffset((decimal)position.X, (decimal)position.Y));
             var bytesPerShow = new List<byte>();
             foreach (var letter in text)
             {
                 if (char.IsWhiteSpace(letter))
                 {
-                    operations.Add(new ShowText(bytesPerShow.ToArray()));
+                    CurrentStream.Add(new ShowText(bytesPerShow.ToArray()));
                     bytesPerShow.Clear();
                 }
 
@@ -262,10 +306,10 @@
 
             if (bytesPerShow.Count > 0)
             {
-                operations.Add(new ShowText(bytesPerShow.ToArray()));
+                CurrentStream.Add(new ShowText(bytesPerShow.ToArray()));
             }
 
-            operations.Add(EndText.Value);
+            CurrentStream.Add(EndText.Value);
 
             return letters;
         }
@@ -322,16 +366,16 @@
 
             resourcesDictionary[NameToken.Xobject] = xobjects.With(key, new IndirectReferenceToken(reference));
 
-            operations.Add(Push.Value);
+            CurrentStream.Add(Push.Value);
             // This needs to be the placement rectangle.
-            operations.Add(new ModifyCurrentTransformationMatrix(new []
+            CurrentStream.Add(new ModifyCurrentTransformationMatrix(new []
             {
                 (decimal)placementRectangle.Width, 0,
                 0, (decimal)placementRectangle.Height,
                 (decimal)placementRectangle.BottomLeft.X, (decimal)placementRectangle.BottomLeft.Y
             }));
-            operations.Add(new InvokeNamedXObject(key));
-            operations.Add(Pop.Value);
+            CurrentStream.Add(new InvokeNamedXObject(key));
+            CurrentStream.Add(Pop.Value);
 
             return new AddedImage(reference, info.Width, info.Height);
         }
@@ -361,16 +405,16 @@
 
             resourcesDictionary[NameToken.Xobject] = xobjects.With(key, new IndirectReferenceToken(image.Reference));
 
-            operations.Add(Push.Value);
+            CurrentStream.Add(Push.Value);
             // This needs to be the placement rectangle.
-            operations.Add(new ModifyCurrentTransformationMatrix(new[]
+            CurrentStream.Add(new ModifyCurrentTransformationMatrix(new[]
             {
                 (decimal)placementRectangle.Width, 0,
                 0, (decimal)placementRectangle.Height,
                 (decimal)placementRectangle.BottomLeft.X, (decimal)placementRectangle.BottomLeft.Y
             }));
-            operations.Add(new InvokeNamedXObject(key));
-            operations.Add(Pop.Value);
+            CurrentStream.Add(new InvokeNamedXObject(key));
+            CurrentStream.Add(Pop.Value);
         }
 
         /// <summary>
@@ -439,16 +483,16 @@
 
             resourcesDictionary[NameToken.Xobject] = xobjects.With(key, new IndirectReferenceToken(reference));
 
-            operations.Add(Push.Value);
+            CurrentStream.Add(Push.Value);
             // This needs to be the placement rectangle.
-            operations.Add(new ModifyCurrentTransformationMatrix(new[]
+            CurrentStream.Add(new ModifyCurrentTransformationMatrix(new[]
             {
                 (decimal)placementRectangle.Width, 0,
                 0, (decimal)placementRectangle.Height,
                 (decimal)placementRectangle.BottomLeft.X, (decimal)placementRectangle.BottomLeft.Y
             }));
-            operations.Add(new InvokeNamedXObject(key));
-            operations.Add(Pop.Value);
+            CurrentStream.Add(new InvokeNamedXObject(key));
+            CurrentStream.Add(Pop.Value);
 
             return new AddedImage(reference, png.Width, png.Height);
         }
@@ -531,7 +575,7 @@
         /// <summary>
         /// Provides access to the raw page data structures for advanced editing use cases.
         /// </summary>
-        public class AdvancedEditing
+        public class ContentStream
         {
             /// <summary>
             /// The operations making up the page content stream.
@@ -539,11 +583,16 @@
             public List<IGraphicsStateOperation> Operations { get; }
 
             /// <summary>
-            /// Create a new <see cref="AdvancedEditing"/>.
+            /// Create a new <see cref="ContentStream"/>.
             /// </summary>
-            internal AdvancedEditing(List<IGraphicsStateOperation> operations)
+            internal ContentStream()
             {
-                Operations = operations;
+                Operations = new List<IGraphicsStateOperation>();
+            }
+
+            internal void Add(IGraphicsStateOperation newOperation)
+            {
+                Operations.Add(newOperation);
             }
         }