There weren't really any dead ends. Mostly because I started with a very simple naive way to draw polygons and improved it incrementally. I didn't implement all those steps, but convinced myself that they would work. I started with a generic plot-individual-pixels-into-tilemap routine. Going by tile-rows and columns with special casing solid tiles came next. That required "convexity" in x direction but at that point I was only thinking of triangles. Then I noticed that avoiding overdraw and working with a tesselation of the screen is probably faster. A that point I also extended it from triangles to polygons. While fleshing out the details of everything I noticed that I don't have to be exact for right-side edges if I draw the polygons in the right order.

There actually was an extension I did, that was scrapped because it just didn't look good. At some point there was support for dithering. That helps with the low color precision of the Mega Drive (3-bit/channel). It only supported 50% checkerboard dither though, which looked odd when animated. I toyed with some ideas on how to improve upon that and discussed them within our demo group, but in the end the decision was to not use dithering.