Still Alive for the Apple II
in roughly 16k
By Deater (Vince Weaver)
vince@deater.net
BACKGROUND
~~~~~~~~~~
A few years back I implemented Valve's Portal in Applesoft BASIC.
At the end it played Still Alive, but in horrible single-channel
speaker beeps. I always wanted to have this sound better.
So here is the end result. Still Alive in 6-Channel Mockingboard
Sound in 80 column with cursor effects. Also in 40 column if
your display can't handle 80 cols. And if you don't have a
Mockingboard, then a simpler version using P. Lutus'
Electric Duet 2-channel audio for the stock speaker.
Fun fact:
The letter 'Z' does not appear at all in the lyrics to the song.
(Noticed when I had to edge comparison for uppercase off by one)
Challenges:
+ 6-channel audio. Really its 4-channel (from a MOD file)
but it actually does load and play audio on all 6 channels.
+ Fitting it all in 48k (want to avoid disk routines if can)
+ Printing the ASCII art (naive implementation takes longer than 50Hz)
The ASCII art is roughly 7k. Thought of decompressing
on the fly, but the LZ4 code is not re-entrant and
the music is already decompressing on the fly.
+ Re-using the Lyrics for both the Mockingboard and Electric Duet
versions.
+ Squeezing the compressed image into memory leaving room for
all the code to be decompressed while leaving enough
room that DOS still has room to load things. It's
an *extremely* tight fit.
+ An odd issue where the 80col display would get corrupted
if we set HIRES without explicitly setting LORES
before doing PR#3
Goal: Binary fits in 16k (16384 bytes)
note size (bytes)
--------------------- ------
initial music player: 2078
add raw ascii art: 9142
add 3-channel music+lyrics,then slim a bit: 18787
initial 40 col support: 18864
have art loading properly 40col: 18910
lz4 encode the ascii art: 15529
revert because lz4 code not re-entrant: 18910
add 4-channel music (KR4): 20128
add cursor (a bit distracting): 20162
feature complete 40 col: 20180
intial 80 col support: 20191
80 col cursor: 20344
strip out some unneeded text printing: 19962
merge ED and MB code: 24993
properly select between versions: 25001
merge the ED and MB lyrics: 22828
80 column ED, wait for keypress+reboot at end: 22852
Crazy compression:
Remove mockingboard detection: 16343
Memory Map:
0000: Zero Page
0100: Stack
0400: Text Page 0 (AUX 0400: 80 column text)
2000: HGR Page0
4000: HGR Page1
9600: DOS 37.5k
C000: I/O Space
D000: ROM
FFFF: END
Plan:
Load compressed 16k image ($4000) at $5900 - $9900
We use MAXFILES 1 to give us some extra room
just before DOS
Decompress ENDING sequence at $1800 - $4000
(writes background to HGR graphics automatically)
STILL_ALIVE:
+ $0800 - $5900
$2e2d of code
$2282 of KR4 music *or*
$0842 of ED music
+ Sound buffers ($3800, 14k) at $5e00 - $9600
b08d7e5851