iTextSharp CreateInk method: curves and corners

Question

I\'m using iTextSharp to draw markup graphics in PDF documents, using PdfAnnotation.CreateInk. I\'m trying to draw rectangles, passing in an array of five co-ordinates. I

Answer 1

Which annotation type to use

I know iTextSharp has a dedicated function for drawing rectangles, but I'm trying to use just one method to draw the various kinds of markup lines I need, and it seems that CeateInk should be able to do that.

Please be aware that iText not merely has separate functions for those different forms, these different functions also create different types of PDF annotations.

In particular the Ink annotation -- which you would like to use for all forms -- is specified as

An ink annotation (PDF 1.3) represents a freehand “scribble” composed of one or more disjoint paths.

(Section 12.5.6.13 - Ink Annotations - ISO 32000-1)

As a freehand “scribble” commonly is not considered to be a sequence of straight lines and sharp corners but instead more soft and rounded; thus, it is only natural that PDF viewers will display an ink annotation given by coordinates of the corners of a rectangle with curves rather than corners.

Of course you can use an appearance stream to provide a visualization of the appearance but that would be a small misuse of this PDF feature.

Instead I would propose you use a different kind of annotation to draw the various kinds of markup lines you need: Polyline annotations. They are specified as:

Polygon annotations (PDF 1.5) display closed polygons on the page. Such polygons may have any number of vertices connected by straight lines. Polyline annotations (PDF 1.5) are similar to polygons, except that the first and last vertex are not implicitly connected.

(Section 12.5.6.9 - Polygon and Polyline Annotations - ISO 32000-1)

iText(Sharp) provides a method for this kind of annotations, too:

/**
 * Creates a polygon or -line annotation
 * @param writer the PdfWriter
 * @param rect the annotation position
 * @param contents the textual content of the annotation
 * @param polygon if true, the we're creating a polygon annotation, if false, a polyline
 * @param vertices an array with the vertices of the polygon or -line
 * @since 5.0.2
 */
public static PdfAnnotation CreatePolygonPolyline(
    PdfWriter writer, Rectangle rect, String contents, bool polygon, PdfArray vertices)

You might eventually still have to create annotations as not all PDF viewers, in particular so called "pre-viewers", generate appearances but instead count on appearances being provided in PDFs they pre-display...

Examples

Without own appearance

using (PdfReader pdfReader = new PdfReader(inputPath))
using (PdfStamper pdfStamper = new PdfStamper(pdfReader, outputStream))
{
    PdfArray vertices = new PdfArray(new int[]{ 100, 100, 300, 300, 100, 300, 300, 100 });
    PdfAnnotation polyLine = PdfAnnotation.CreatePolygonPolyline(pdfStamper.Writer, pdfReader.GetPageSize(1),
        "", false, vertices);
    polyLine.Color = BaseColor.GREEN;
    pdfStamper.AddAnnotation(polyLine, 1);
}

adds this:

in PDF viewers supporting annotations including appearance generation according to the specification.

With own appearance

using (PdfReader pdfReader = new PdfReader(inputPath))
using (PdfStamper pdfStamper = new PdfStamper(pdfReader, outputStream))
{
    Rectangle pageSize = pdfReader.GetPageSize(1);
    PdfArray vertices = new PdfArray(new int[] { 100, 100, 300, 300, 100, 300, 300, 100 });
    PdfAnnotation polyLine = PdfAnnotation.CreatePolygonPolyline(pdfStamper.Writer, pageSize,
        "", false, vertices);
    polyLine.Color = BaseColor.GREEN;

    PdfAppearance appearance = PdfAppearance.CreateAppearance(pdfStamper.Writer, pageSize.Width, pageSize.Height);
    appearance.SetColorStroke(BaseColor.RED);
    appearance.MoveTo(100, 100);
    appearance.LineTo(300, 300);
    appearance.LineTo(100, 300);
    appearance.LineTo(300, 100);
    appearance.Stroke();

    polyLine.SetAppearance(PdfName.N, appearance);
    pdfStamper.AddAnnotation(polyLine, 1);
}

adds this

in PDF viewers supporting annotations which bring along their annotation according to the specification.

(I explicitly used a different color in my appearance to make sure the PDF viewer shows my appearance and does not create one itself.)