the setXORColor()

[bhowardsoftware]

I recently switched from a paid for PDF library to PDFBox and pdfbox-graphics2d. Working great!

The only issue is we need an setXORColor() equivalent. Based on other discussions (e.g. stackexchange) others have the same need. However, when you get to the root of what developers really need you find it is just the blend mode from the PDF Spec.

Here is the idea:

• add a method setPDFBlendMode(x) to the PdfBoxGraphics2D
• x could be a constant for the various PDF blend modes - including multiply
• Adjust where PdfBoxGraphics2D sets the Composite to set the blend mode.

I have hacked the source to do this based on an unused AlphaComposit constant and it works well. I can share my one line of code (below) but this could be done better with the above idea. No problem taking a stab at it, but I don't know how this group makes things happen.

added line 475 as shown below.
case AlphaComposite.DST_ATOP:
break;
to
case AlphaComposite.DST_ATOP:
blendMode = COSName.MULTIPLY; // ok, a hack! But gets the same as setXORMode(Color.white);setColor(color);
break;

Regardless - good library! saved me from crafting my own (again).

[rototor]

Well, as I'm the sole maintainer and very busy since some years now with a lot of other stuff, I would really appreciate if you could just provide a PR with this change. In this PR should be

• this change
• a test driver extending PdfBoxGraphics2DTestBase and exporting an example using XOR. See e.g., FontTest::testAntonioFont() for a minimal example. Those test driver export both a PNG drawn with the normal Java Graphics2D API and an PDF export to compare the results. They are not strictly speaking a formal test driver, as there is no assert in them. They are just to exercise the code paths and. The check that the result is fine has to always be done manually. I.e., by comparing the PNG with the PDF. They are stored in the Maven target directory.

You can target the 3.0 version for PDFBox 3 or the 0.n version for PDFBox 2, what ever you need. I'll port that to the other version. I can also create a new release if you need that.

But for more I currently just lack the time. And at the moment it does not look like that this is changing anytime soon...