The Camborne School of Mines Geothermal Energy Project had a home-grown 3-dimensional display package, written in Fortran and running on DEC Vax machines. Working for Haydn Scholes, with other maintainers, I added patches including (most strenuously) additions to extend from wireframe into 3D polygon display
It looks dated now but was perfect for the technology of the time. I did various amendments but the meatiest involved some serious maths for the display of solid objects. Up until then, all the display was lines and crosses, which is a whole deal less difficult than solids, where you cannot just plot one object on top of another.
I used "Newells" algorithm, lots of trigonometry and brainache, plus of course help from the cleverer guys around me. The various intermediate buggy results looked like they had been scrambled by the wrong end of Scotty''s teleporter, but eventually things came right. The purpose was to display data from a rock-fracture modelling package. The geophysicists (in whose mathematical shadow I cowered) had some clever predictions of how fluids and rock mixed under pressure 2km - 6km below ground, and could guess at structures of 3D crazy paving fracture networks.