Q:
In our PDFNet-based software, we support axial shadings. But in our case, any of the source colors can have an independent alpha. So, we can have a gradient going from an opaque blue to a 50% transparent red, and we need that in the exported PDF. How can we do so?
To do this, you would need to create create two axial shadings. One would contain the colors, and the other would be a SoftMask containing the transparency.
This article describes how to create a soft mask from vector content (like an axial shading):
https://groups.google.com/d/msg/pdfnet-sdk/gKO8exFlxJg/ShnV6Z64g4cJ
This article demonstrates radial softmasks, and gives example PDFs you can examine with CosEdit:
http://www.pdfvt.com/PDFVT_TransparencyGuide.html#_Toc243664699