iTextSharp Adding Background Color to Watermark Text - vb.net

Question

I am adding watermark text to PDFs in a class library I have created. The code I posted below works fine, however the watermark is sometimes difficult to read because it overlays with content on the PDF. How would I go about adding a white background color around the watermark text? I basically would like the watermark text to be surrounded inside a white rectangle the size of the text. Thanks
Public Function AddWatermarkText(ByVal tempDirectory As String) As String
' Just return the full path of the PDF if we don't need to add a watermark.
If Me.Document.RevRank <> 0 OrElse Me.Document.ReleaseDate Is Nothing Then Return Me.FullPath
Dim reader As iTextSharp.text.pdf.PdfReader = Nothing
Dim stamper As iTextSharp.text.pdf.PdfStamper = Nothing
Dim gstate As New iTextSharp.text.pdf.PdfGState()
Dim overContent As iTextSharp.text.pdf.PdfContentByte = Nothing
Dim rect As iTextSharp.text.Rectangle = Nothing
Dim watermarkFont As iTextSharp.text.pdf.BaseFont = Nothing
Dim folderGuid As Guid = Guid.NewGuid()
Dim outputFile As String = tempDirectory & System.IO.Path.DirectorySeparatorChar & folderGuid.ToString() & System.IO.Path.DirectorySeparatorChar _
& Me.Document.Prefix & Me.Document.BaseNumber & Me.Document.Revision & ".pdf"
' Create the temp directory to place the new PDF in.
If Not My.Computer.FileSystem.DirectoryExists(tempDirectory) Then My.Computer.FileSystem.CreateDirectory(tempDirectory)
My.Computer.FileSystem.CreateDirectory(tempDirectory & System.IO.Path.DirectorySeparatorChar & folderGuid.ToString())
reader = New iTextSharp.text.pdf.PdfReader(Me.FullPath)
rect = reader.GetPageSizeWithRotation(1)
stamper = New iTextSharp.text.pdf.PdfStamper(reader, New System.IO.FileStream(outputFile, IO.FileMode.Create))
watermarkFont = iTextSharp.text.pdf.BaseFont.CreateFont(iTextSharp.text.pdf.BaseFont.HELVETICA_BOLD, _
iTextSharp.text.pdf.BaseFont.CP1252, _
iTextSharp.text.pdf.BaseFont.NOT_EMBEDDED)
gstate.FillOpacity = 0.9F
gstate.StrokeOpacity = 1.0F
' Add the watermark to each page in the document.
For i As Integer = 1 To reader.NumberOfPages()
overContent = stamper.GetOverContent(i)
With overContent
.SaveState()
.SetGState(gstate)
.SetColorFill(iTextSharp.text.BaseColor.BLUE)
.Fill()
.BeginText()
.SetFontAndSize(watermarkFont, 8)
.SetTextMatrix(30, 30)
If Me.Document.RevRank = 0 AndAlso Me.Document.ReleaseDate IsNot Nothing Then
.ShowTextAligned(iTextSharp.text.Element.ALIGN_LEFT, UCase(String.Format("CONTROLLED DOCUMENT – THIS COPY IS THE LATEST REVISION AS OF {0}" _
, Date.Now.ToString("ddMMMyyyy"))), 10, rect.Height - 15, 0)
End If
.Fill()
.EndText()
.RestoreState()
End With
Next
stamper.Close()
reader.Close()
Return outputFile
End Function

Answer 1

I usually like to have code that you can just plop in but unfortunately you're code is a little too domain-specific to provide a direct answer (lots of Me.* that we have to guess at) but I can still get you there with a little code refactoring.
To do what you want to do you have to measure the string that you are drawing and then draw a rectangle to those dimensions. The PDF spec doesn't have a concept of "background color" for text and any implementation that makes it look like it does is really just drawing rectangles for you. (Yes, you can highlight text but that's an Annotation which is different.)
So first I'm going to pull things out into variables so that we can reuse and adjust them easier:
''//Text to measure and draw
Dim myText As String = UCase(String.Format("CONTROLLED DOCUMENT – THIS COPY IS THE LATEST REVISION AS OF {0}", Date.Now.ToString("ddMMMyyyy")))
''//Font size to measure and draw with
Dim TextFontSize As Integer = 8
''//Original X,Y positions that we were drawing the text at
Dim TextX As Single = 10
Dim TextY As Single = rect.Height - 15
Next we need to calculate the width and height. The former is easy but the latter requires us to first get the Ascent and Descent of the text and then calculate the difference.
''//Calculate the width
Dim TextWidth As Single = watermarkFont.GetWidthPoint(myText, TextFontSize)
''//Calculate the ascent and decent
Dim TextAscent As Single = watermarkFont.GetAscentPoint(myText, TextFontSize)
Dim TextDescent As Single = watermarkFont.GetDescentPoint(myText, TextFontSize)
''//The height is the difference between the two
Dim TextHeight As Single = TextAscent - TextDescent
(NOTE: I'm not sure if GetWidthPoint(), GetAscentPoint() and GetDescentPoint() work as desired with multi-line text.)
Then you probably want to have some padding between the box and text:
''//Amount of padding around the text when drawing the box
Dim TextPadding As Single = 2
Lastly, somewhere before you setup and draw the text you want to first draw the rectangle:
''//Set a background color
.SetColorFill(BaseColor.YELLOW)
''//Create a rectangle
.Rectangle(TextX - TextPadding, TextY - TextPadding, TextWidth + (TextPadding * 2), TextHeight + (TextPadding * 2))
''//Fill it
.Fill()