23 lines
1.1 KiB
Plaintext
23 lines
1.1 KiB
Plaintext
512 byte bootsector demo for the Apple II
|
|
|
|
I had more elaborate plans for this one, including having the duck
|
|
appear randomly over the screen. Ran out of time and also out of bytes.
|
|
|
|
I also wanted a quacking noise, but couldn't figure out how to do that
|
|
in the bytes available.
|
|
|
|
This is an actual bootsector (well, Apple II has 256 byte disk sectors,
|
|
but the disk boot ROM will let you specify more than one to load). Apple
|
|
II loads the boot sector starting at $800, which is a problem for a
|
|
Lo-res demo as that's also the location of lo-res PAGE2 graphics. So I
|
|
had to waste a chunk of code to move the code out of the way before
|
|
running it.
|
|
|
|
The spinning lo-res logo is actually using the hi-res shape table routines.
|
|
How is that possible? It draws a small rotating copy of the logo to
|
|
the upper-left corner of the (not-displayed) hi-res screen. Then the code
|
|
copies this (while adding more colors) to the lo-res screen. It's hard
|
|
to do this quickly, to save time and space it actually destroys the hi-res
|
|
image by shifting it down to zero while reading it out,
|
|
but this is actually good as then we don't have to clear the screen.
|