How to draw vertical gradient in iTextSharp?

问题

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.SetShadingFill(pattern);
pdfContentByte.Rectangle(0, 0, document.PageSize.Width, 70);
pdfContentByte.Fill();

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 like some one did here (Does iTextsharp support multi color diagonal gradients?) did not solve the problem. I also tried to rotate the document but that didn't work as well.

回答1:

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));
    document.open();
    PdfShading shading = PdfShading.simpleAxial(writer,
            0, pageSize.getHeight(),
            0, 0,
            BaseColor.WHITE, BaseColor.GREEN);
    PdfShadingPattern pattern = new PdfShadingPattern(shading);
    PdfContentByte canvas = writer.getDirectContent();
    canvas.setShadingFill(pattern);
    canvas.rectangle(0, 0, pageSize.getWidth(), pageSize.getHeight());
    canvas.fill();
    document.close();
}

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

来源：https://stackoverflow.com/questions/34433510/how-to-draw-vertical-gradient-in-itextsharp

标签

itext

gradient