PdfPCell background color ignoring alpha channel of an rgba

[alaingaudreau]

Is it expected behavior for PdfPCell to ignore the alpha channel value when you setBackgroundColor with a Color(r,g,b,a)?

I haven't seen anything in the docs/javadocs for this class regarding the alpha channel.

[razilein]

https://github.com/LibrePDF/OpenPDF/blob/master/openpdf/src/main/java/com/lowagie/text/pdf/PdfContentByte.java#L2262

I've found this. The alpha channel is ignored, because it's value is not delivered at this point.

The alpha channel should be delivered to this method:
https://github.com/LibrePDF/OpenPDF/blob/master/openpdf/src/main/java/com/lowagie/text/pdf/PdfContentByte.java#L2166

But I don't know how to set this. I've found that there is the parameter "S" which is for transparency.

See https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/PDF32000_2008.pdf
on page 347 (Table 144)

Maybe someone else can help with this example:

    private static void cellWithRgb(Document doc) {
        PdfPCell redCell = new PdfPCell(new Paragraph("Red"));
        redCell.setBackgroundColor(new Color(255, 0, 0, 50));
        
        PdfPCell greenCell = new PdfPCell(new Paragraph("Green"));
        greenCell.setBackgroundColor(new Color(0, 255, 0, 100));
        
        PdfPCell blueCell = new PdfPCell(new Paragraph("Blue"));
        blueCell.setBackgroundColor(new Color(0, 204, 255, 255));

        final PdfPTable table = new PdfPTable(1);
        table.addCell(redCell);
        table.addCell(greenCell);
        table.addCell(blueCell);

        doc.add(table);
    }

[sixdouglas]

Here you have an example of the ContentByte in use:

https://github.com/LibrePDF/OpenPDF/blob/master/pdf-toolbox/src/test/java/com/lowagie/examples/directcontent/colors/Transparency.java

With this sample you see how to write table using DirectContent:

https://github.com/LibrePDF/OpenPDF/blob/master/pdf-toolbox/src/test/java/com/lowagie/examples/directcontent/pageevents/EndPage.java

Maybe you can manage using this for the background color. Here is a sample of code.

Document document = new Document(PageSize.A4, 50, 50, 50, 50);
try {
    PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream("transparency-1.pdf"));
    document.open();
    Rectangle page = document.getPageSize();
    PdfContentByte cb = writer.getDirectContent();
    cb.saveState();
    PdfGState gs1 = new PdfGState();
    gs1.setFillOpacity(0.5f);
    cb.setGState(gs1);
    PdfPTable head = new PdfPTable(3);
    for (int k = 1; k <= 6; ++k) {
        PdfPCell cell = new PdfPCell(new Phrase("head " + k));
        cell.setBackgroundColor(new Color(0, 204, 255));
        head.addCell(cell);
    }
    head.setTotalWidth(page.getWidth() - document.leftMargin() - document.rightMargin());
    head.writeSelectedRows(0, -1, document.leftMargin(), page.getHeight() - document.topMargin() + head.getTotalHeight(), cb);
    cb.restoreState();
    cb.sanityCheck();
}
catch (Exception de) {
    de.printStackTrace();
}
document.close();

But as you can see the borders and the text inherit also of the transparency :/

[mkl-public]

Related: https://stackoverflow.com/a/56954685/1729265

Support for transparent cell background colors has been added in iText 5.5.7, more exactly in git commit 09ccaa728830a404e92fc3040dd3626198576fef.
Depending on the exact version of iText you may try and use a PdfPCellEvent implementation instead of setting the background color with setBackgroundColor. In that implementation you'd have to first save the graphics state, then set a PdfGState with transparency, fill the cell rectangle with the color, and restore the graphics state again.

[sixdouglas]

@asturio maybe we need to build a release to make these changes available to all

[testn]

so this one should be closed?