This is a vapor-lock cycle-counting demo for the Apple II.
It might eventually become a full game.
Video
Capture of older v0.5 on actual Apple IIe hardware.
A more recent capture of v0.8 with some minor changes in the
AppleWin emulator:
Updated video
Controls
Level 3: Use A/Z for up and down, space to shoot.
Level 6: Use arrow keys, anything else quits.
Notes
This game will run on an original Apple II from 1977! The magic
is all in cycle counting and
Vapor Lock.
No double lores or double hires
is used.
The title is 40x48 interlaced lores, switching between page1 and page2
each scanline to give the illusion of more than 15 colors.
Level 3 uses the 40x192 beam-racing mode to get some really smooth
vertical motion. This is the same mode from my
rasterbars demo.
Level 6 has a line of textmode at top, then the rest of
the screen is a complex split of HGR and GR.
Eventually the plan is to switch between page1/page2 to get
40x96 higher-quality rasterbars.
Future notes
Right now the cycle counting is pretty elaborate, but the rasterbars are
only 40x48 not 40x96. This is because you can't switch HI/LO and PAGE1/PAGE2
both in time to do the bar effect. It should be possible to do this in
the end if we mirror the HGR image on both PAGE1/PAGE2, but this takes
16k of RAM so will have to wait a bit (for reasons that will eventually
be revealed). [note from 2026 I can't remember what my 2018 self
was talking about here]
The other trouble is having to write the graphics/sprites to both
PAGE1 and PAGE2, we might have to interlace every other frame for
that to work.
Screenshots
New 40x192 enhanced Level3:
Mixed hires/lores/text Level6:
System Requirements
Should in theory work on any Apple II system with 48k of RAM.
Only tested on Apple IIe Platinum. Works in AppleWin and newer versions
of MAME.
Certain modes probably won't work on older Apple IIgs systems with the
broken lo-res PAGE2 support but I haven't checked. I'm not sure if
the usual workaround will work or not.
Downloads:
You can try it on the Internet Archive
here,
but as of 2026 the version
of MAME they use in-browser doesn't seem to support the PAGE1/PAGE2
page-flipping.
Development Log
3 October 2026
Released 0.8. Mostly cleaned up to use the QLOAD infrastructure and
made the code modular, also improved key handling as Saturn.
Otherwise should be no changes in functionality.
13 June 2019
Released 0.7 which makes the surrounding game a bit easier to use.
Returns to title screen after game over, which is nice, but some data
structures aren't cleaned up 100% and it will be a pain to fix that.
Released 0.6 which adds the new 40x192 15-color "Level3". This came out
of my rasterbars demo, as someone asked me if the mode was good for
anything useful. Game has its issues, but it is playable.
8 October 2018
Released version 0.5. This code was reused in the
Apple II Megademo.
