Add Gradient Shading using Stamper - itext

Question

I have code that uses iTextSharp to add a variety of colored rectangles to an existing PDF document using the PdfStamper object with code like the following:
Dim reader As New PdfReader(byte_contets_of_PDF_file)
Dim stamper As New PdfStamper(reader, someOutputBuffer)
Dim under As PdfContentByte = stamper.GetUnderContent(pageNumber)
under.SetColorFill(BaseColors.RED)
under.Rectangle(x, y, rectWidth, rectHeight)
under.Fill()
This works swimmingly for drawing monochromatic rectangles on an existing PDF document, but I was hoping I could place rectangles that use a color gradient.
My research has turned up examples using the PdfShading and PdfShadingPattern objects, but those require a PdfWriter. To my understanding, the PdfWriter is used for creating new PDFs and not for updating existing PDFs.
Is it possible to add rectangles to an existing PDF document that have a gradient?
Thanks

Answer 1

I assume you have read the answer to this question: How to add a shading pattern to a custom shape
I assume that your problem is that you don't know which parameter to use instead of writer.
If that is the case, use 'stamper.GetOverContent(p)' instead of writer.DirectContent and use stamper.Writer instead of writer:
int p = 1; // or whatever page number applies
PdfContentByte canvas = stamper.GetOverContent(p);
float x = 36;
float y = 740;
float side = 70;
PdfShading axial = PdfShading.SimpleAxial(writer, x, y,
x + side, y, BaseColor.PINK, BaseColor.BLUE);
PdfShadingPattern shading = new PdfShadingPattern(axial);
canvas.SetShadingFill(shading);
canvas.MoveTo(x,y);
canvas.LineTo(x + side, y);
canvas.LineTo(x + (side / 2), (float)(y + (side * Math.sin(Math.PI / 3))));
canvas.ClosePathFillStroke();