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69 lines
2.5 KiB
Plaintext
69 lines
2.5 KiB
Plaintext
KFEST18 SUPER RASTERBAR 2K DEMO
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by deater (Vince Weaver) vince@deater.net
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http://www.deater.net/weave/vmwprod/kfest18/
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Written for the Kansasfest Hackfest. Won 2nd place.
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I started work on this on the morning of Wed Jul 18th and finished
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early in the AM on Saturday July 21st.
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NOTE: If you run the demo and the sound is scratchy and/or the graphics
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corrupted, reboot until it works. Sometimes the vapor-lock doesn't
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happen like it should and I'm not sure why.
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How it works:
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The Apple II lo-res mode is usually limited to 40x48 mode.
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However, there are two graphics pages that can be flipped
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between with a soft-switch.
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If you switch between page0 and page1 at just the right time
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(every 2 scan lines) you can create a pseudo 40x96 graphics
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mode, using all 15 lo-res colors.
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This is *not* double lo-res (that requires 128k of RAM + IIe
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and is an 80x48 graphics mode). This mode in theory will
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work on an original II.
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Of course there's no VBLANK notification or HSCAN interrupts
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on Apple II. So you have to read the "floating bus" to find
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out when a scan line begins, and then count cycles to find
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out where to switch things.
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All the calculations for the raster bar, mockingboard sound,
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and scrolling text are done during the 4550 cycles of VBLANK.
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To save space, only two channels of audio are played.
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More technical info:
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I made the music from the sheet music using a weird text-editor
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based tracker I've written. There's a one off conversion tool
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in my separate vmw-meter.git repository called "ym5_to_kf"
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that takes the generated ym5 and strips it down for the demo.
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I did not do any size optimization at all, in fact the opposite
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as I am cycle counting here, so lots of time spent wasting cycles
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so both sides of branches match up. Also on 6502 if a branch
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crosses a page boundary it takes a cycle penalty, so to simplify
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things I have .align codes all over.
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This doesn't matter though because I compress with qkumba's lz4
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and that forgives many sins.
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For the timing loops, I have a simple nested timing loop with X and Y.
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I have a C program I use that I input how many cycles I want and it
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prints all possible options with 10 cycles or so. If no exact match
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is possible I pad with NOPs or similar to get the right amount.
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This was all written in 6502 assembly, using ca65 asm on Linux
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and tested in AppleWin running under wine.
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Greets:
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Code by: deater (Vince Weaver)
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LZ4 code: qkumba
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Music: Muda Kingdom from Super Mario Land (gameboy) by Hirokazu Tanaka
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transcribed from sheet music by G-Han
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