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I can make a horizontal gradient, but how do I make it vertical?

I am trying to draw a vertical gradient at the bottom of an iTextSharp pdf document:

PdfShading shading = PdfShading.SimpleAxial(pdfWriter, 0, document.PageSize.Height, document.PageSize.Width, 0, BaseColor.WHITE, BaseColor.GREEN);
PdfShadingPattern pattern = new PdfShadingPattern(shading);
pdfContentByte.Rectangle(0, 0, document.PageSize.Width, 70);
This creates a gradient at the exact position I want it to be created, but the gradient is horizontal from left (white) to right (green). I want the gradient to be vertical from top (white) to bottom (green). Modifying the coordinates did not solve the problem. I also tried to rotate the document but that didn't work as well.

Posted on StackOverflow on Dec 23, 2015 by Norman

You are using the wrong coordinates. In Java, you'd need something like this:

public void createPdf(String dest) throws IOException, DocumentException {
    Rectangle pageSize = new Rectangle(150, 300);
    Document document = new Document(pageSize);
    PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream(dest));
    PdfShading shading = PdfShading.simpleAxial(writer,
            0, pageSize.getHeight(),
            0, 0,
            BaseColor.WHITE, BaseColor.GREEN);
    PdfShadingPattern pattern = new PdfShadingPattern(shading);
    PdfContentByte canvas = writer.getDirectContent();
    canvas.rectangle(0, 0, pageSize.getWidth(), pageSize.getHeight());

See GradientTopToBottom for the full sample code.

Do you see the difference?

  • You go from the left-top corner (0, document.PageSize.Height) to the right-bottom corner (document.PageSize.Width, 0). That's a diagonal.

  • You want to go from the top (0, document.PageSize.Height) to the bottom (0, 0) which leads to the following result: gradient_top_to_bottom.pdf

    Gradient from top to bottom

    Gradient from top to bottom