That was done with only 2 constraints: to use real memory snapshots (real ROM and VRAM snapshot from MAME), and to have a pixel-perfect output.
That being said, this picture of my DE1 FPGA board rendering a similar image from Metal Slug 1 might not seem like anything new.
That's because the added constraint isn't quite visible in the resulting image: all the signals used to produce it are 100% accurate (= exactly the same as the ones generated by a real NeoGeo system) !
No hackery and over-complicated logic, just a bunch of guesses that fit in just right.
Sprites stil seem to be a long way to go, but most of the required timings and video access slots are correct now, so it's really a matter of getting the SDRAM to work, filling it with some sprite graphics, and make the line buffers work.
That's about all I'll be able to do on that DE1 board due to the lack of memory. Keep in mind that Metal Slug does run in simulation, but isn't running on the board here, it's ony graphics ROMs and a VRAM snapshot.
Free post because no expenses :)