V1.2 notes -- 12/18/2019
Should auto-detect the slot the Mockingboard is in.
V1.1 notes -- 12/21/2019
Added some code to detect Apple II+ vs IIe, as the text sliding code
looked worse on the IIe because the font is offset by a line.
Also reduced the volume on drums on the music a bit to try to make
it sound a bit less harsh.
V1.0 notes -- 12/20/2019
This came out of wanting to see if the Apple II could do the effect
found in the 2018 "HAPPY CHIPPIE XMAS" demo by ThePetsMode.
In the end it was sort of possible, but it might look cooler in
a 40x96 mode.
The music is "jingle.xm" by Michu, downconverted to a
It's a single scene, running at 30Hz. It uses vapor lock and cycle counting
to get some unusual things on the Apple II display.
The code is loaded at $2000 (HGR page1) and decompressed to
$4000 (HGR page2) which accounts for the static you see
at load time.
The top is text, alternating page1/page2 to allow an interlaced effect.
There's only room for 256bytes of scroll text, which is why
it's a bit abbreviated.
On the sides is snow falling on the HGR highres screen
Mid-screen the display turns to 15-color LORES to draw the sine-wave
At the bottom 40x96 page1/page2 mode is used to make the higher-res
than normal text.
The tree is updated on odd screen refreshes, the music/snow/text is
updated on even.
For more info on vapor-lock / cycle counting see some of my other
demos, the megademo is a good place
On original Apple II/II+ there are some screen glitches. This is because
the older hardware really doesn't like switching from GR to HGR mid-screen.
Also the graphics hardware timing is 1-cycle different on II+ vs IIe
so I really should be detecting and patching the code to account for this.
I am too lazy to try to fix that, so you will see the glitch: