There are only a couple changes that I've left in:
1. On normal missions, the edge of the screen still doesn't slow you down.
2. The shop still does not have the old bug where selling was based on the price of the next item.
3. Not sure about this, but some powerups don't spawn if they're of no use to you; I believe this was not in the original, but it's been left in anyway.
4. Not sure about this either, but I believe the original had the 3-way spread much wider. This has not been adjusted for Classic difficulty.
Other than those three, Classic difficulty is now exactly the same,
including a re-implementation of the whole "score" system where destroying
a ship nets you money instantly and the absurd system where you buy only
10 plasma capacity at a time. I might adjust 1, 3, and/or 4 above later
on.
Limited damage prevention to only at the "low" and "critical" levels,
plus added a delay for when damage is first inflicted by rays.
This prevents ships with multiple concentrated shots from having
a disadvantage, and it helps make rays easier to avoid at the same
time (just get out of the ray in time and you don't take damage).
Of course, neither of these apply to Classic difficulty, although
the ray damage delay does apply to Nightmare difficulty (which,
given how unpredictable rays are, I think is quite reasonable).
Limits the damage you take somewhat. Basically, this is intended
to prevent sudden deaths; if it doesn't look like you're dying,
you probably won't suddenly get axed. Of course, this is disabled
in Classic difficulty.
The mistake caused the Classic game to deviate from the original
by not allowing Kline to drop mines in the Elamale mission. For
some reason I accidentally put that check in for Moebo instead.
Whoops!
At first I was going to just not bother with the resizing thing, but
then I found out that SDL actually has a scaling function built-in.
So rather than depending on SDL_gfx for this one purpose that never
sees the light of day in practice, I have handed that job over to
that function.
The fake "windowed fullscreen" is less invasive, but it sometimes
causes ugly artifacts and as a general rule isn't really all that
useful.
However, I also defined it in defs.h, so that it can be more easily
changed in the future.