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