I started just hacking games for pokes, but moved on to picking them apart to see how they worked. Some did seem to be quite a mess, but others were obviously very well structured. Starion and Starquake are the ones that stick in my mind most.
Starion's gameplay was a bit dull IMO, but the code was excellent. Aside from the full-screen countdown the vector graphics were the fastest around at the time. The line drawing was unrolled to all 8 possible directions, to be as fast as possible. The back buffer was cleared with the stack and after drawing it was copied to the display using the stack again. As expected, the vector calculations were done as fixed point with the low byte holding the fractional part. Trig used look-up tables with rotations done cummulatively rather than from scratch so visible errors crept in if not recalculated after a while. The ship data relied on most shapes being symmetrical for parallel drawing on each sides, though it didn't have to be used. All round it was the kind of things you'd expect from a Maths student/graduate. I even managed to extract enough of the whole engine to design my own shapes to rotate with the keyboard - might even still have a +D snapshot of it somewhere!
I remember Starquake for being very modular overall, so easy to hack and pick apart. Superb game too, with perfect use of colour and sound, and all running at a silky smooth 50Hz. The sprites were all drawn at the start of the interrupt, and using the stack so in-game Multiface snapshots could easily corrupt them. Interrupts were also re-enabled during their drawing, as it expected no further interrupt to occur until the next frame. Each of the scenery graphics had an 8x6 bit array for used squares, and were followed by 8 data and 1 attr byte for each used block. Room definitions just picked a graphic number and position. The bright bit was used for scenery collision detection rather than keeping track separately, with bright items being solid. If you reset the bright bit from a Multiface program (as I did) you can pass through everything! I remember extracting the sound effects routine too, which I didn't fully understand but I remember being surprisingly compact for the wide range of sounds it produced. I can't quite remember how many bytes defined each effect but I don't think it was more than about 10.
On the other side, I remember being horrified that Manic Miner and/or JSW use LDIR for moving around display data. They kept a copy of the empty room, and for each frame they would LDIR that to a working space, then add the sprites, then LDIR to the main screen. Early days I suppose, and the gameplay more than makes up for it
There were so many other great games that it's hard to know where to start listing them...
Si
