Wrap old content when flattening fields

DEVSIX-2741

Author: LodrKumquat

forms/src/main/java/com/itextpdf/forms/PdfAcroForm.java

@@ -635,6 +635,7 @@ public void flattenFields() {
             initialPageResourceClones.put(i, resources == null ? null : resources.clone());
         }
 
+        Set<PdfPage> wrappedPages = new LinkedHashSet<PdfPage>();
         PdfPage page;
         for (PdfFormField field : fields) {
             PdfDictionary fieldObject = field.getPdfObject();
@@ -683,7 +684,8 @@ public void flattenFields() {
                     if (page.isFlushed()) {
                         throw new PdfException(PdfException.PageAlreadyFlushedUseAddFieldAppearanceToPageMethodBeforePageFlushing);
                     }
-                    PdfCanvas canvas = new PdfCanvas(page);
+                    PdfCanvas canvas = new PdfCanvas(page, !wrappedPages.contains(page));
+                    wrappedPages.add(page);
 
                     // Here we avoid circular reference which might occur when page resources and the appearance xObject's
                     // resources are the same object

forms/src/test/java/com/itextpdf/forms/PdfFormFieldTest.java

@@ -64,6 +64,8 @@ This file is part of the iText (R) project.
 import com.itextpdf.kernel.pdf.canvas.PdfCanvas;
 import com.itextpdf.kernel.utils.CompareTool;
 import com.itextpdf.layout.Canvas;
+import com.itextpdf.layout.Document;
+import com.itextpdf.layout.element.AreaBreak;
 import com.itextpdf.layout.element.Paragraph;
 import com.itextpdf.test.ExtendedITextTest;
 import com.itextpdf.test.annotations.LogMessage;
@@ -887,4 +889,34 @@ public void regenerateMaxLenCombTest() throws IOException, InterruptedException
             Assert.fail(errorMessage);
         }
     }
+
+    @Test
+    public void wrapPrecedingContentOnFlattenTest() throws IOException, InterruptedException {
+        String filename = destinationFolder + "wrapPrecedingContentOnFlattenTest.pdf";
+        PdfDocument pdfDoc = new PdfDocument(new PdfWriter(filename));
+        PdfCanvas canvas = new PdfCanvas(pdfDoc.addNewPage());
+        canvas.setFillColor(ColorConstants.MAGENTA);
+
+        PdfAcroForm form = PdfAcroForm.getAcroForm(pdfDoc, true);
+        PdfTextFormField[] fields = new PdfTextFormField[4];
+        for (int i = 0; i < 4; i++)
+            fields[i] = PdfFormField.createText(pdfDoc, new Rectangle(90, 700 - i * 100, 150, 22), "black" + i, "black");
+        form.addField(fields[0]);
+        form.addField(fields[1]);
+        Document doc = new Document(pdfDoc);
+        doc.add(new AreaBreak());
+        canvas = new PdfCanvas(pdfDoc.getPage(2));
+        canvas.setFillColor(ColorConstants.CYAN);
+        form.addField(fields[2]);
+        form.addField(fields[3], pdfDoc.getFirstPage());
+        form.flattenFields();
+
+        pdfDoc.close();
+
+        CompareTool compareTool = new CompareTool();
+        String errorMessage = compareTool.compareByContent(filename, sourceFolder + "cmp_wrapPrecedingContentOnFlattenTest.pdf", destinationFolder, "diff_");
+        if (errorMessage != null) {
+            Assert.fail(errorMessage);
+        }
+    }
 }