The Sega Saturn and Transparency
Last year, I wrote a fairly complete Genesis (MegaDrive) emulator in C++, for education purposes, that contains a full VDP emulation. The VDP in Megadrive is the father of the VDPs on Saturn, so you can have a look to see how it works:
https://github.com/rasky/genemuThe code should be quite easy to read, as I wrote it to be close to what the hardware does, without any additional complexity for optimizations.