Above are current work in progress screenshots showing the state of Daggorath's graphics.
Before going with the implementation shown, I looked a lot into how to take the frame buffer pixels and convert to something that looks authentic. There is a large body of existing work on processing emulator frame buffers but no existing work I found looked promising. For many games with iconic pixel art, the best bet seems to be to just display square pixels, completely unfiltered. That is not the case for Daggorath however, lines are the iconic element in its graphics.
I decided to try starting with line primitives and work from there to reproduce the original look of the game. I have kept what worked out well: maintaining the same line width the as original; rounding the corners to match the rounding caused by the CRT beam; and, a lot of fiddly work to get the dotted lines to have correct screen area and positioning. I am very happy with how the first person view looks, it feels correct to me and it meets my goal of avoiding distracting artifacts never present in the original.
Overall though, things feel wrong if the display is just black and white. On original hardware everything displayed is subject to considerable color artifacting due to limitations of the video hardware. The text is most affected, almost solid in color. To mimic this I have colored the text in my reproduction to match. Sort of. It does not look right, but overall the coloring is represented. I am not really happy with it but don't have any ideas on how to improve it either.
Time permitting I will experiment with a mild phosphor glow effect but otherwise this may be as good as I can get it.