Lovebyte 2022 Apple II sizecoded Demos

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Presentations

Source Code

The Entries

Oldschool 512B Bootsector -- Flyer

This one is almost like a video game, flying your ship across a retro-80s landscape. The graphics take about half the space, the other half is a stripped down Mockingboard player with music by MA2E.

The graphics are done using calls into the Apple II ROM. The gateways and ship are shape tables drawn with XDRAW. (you may notice the gateways are just the ship shape scaled up). The frame rate is quite slow, there are many potential ways to speed things up but none of them are easy to do it only 256 bytes. It does do page flipping to avoid flicker. Since the code is xor-ing the shapes to the screen, we can do the invert-the-background trick with minimal extra code, but it was hard to synchronize that to the music as the frame rate is much slower than the music player.

The sound takes some shortcuts too. It assumes a Mockingboard in Slot#4 and only plays sound out of the left audio channel to save space. The player is optimized for the specific song.

This one is a boot-sector demo. You might say, aren't Apple II boot-sectors 256 bytes? Yes they are, but you can specify in the first byte how many sectors to load, so we specify two (though note, disk sectors are interleaved, so you don't just write the second sector immediately following the first, but actually at offset 7).

On Apple II machines a boot sector program is loaded at $800, the first byte is how many sectors, and then the loader (which fits entirely in 256B of ROM on the diskII controller card!) jumps to $801 to start executing. Typically the first thing you do is spend 3 bytes of code turning off the floppy motor.

As a boot sector, the remaining 140k of the floppy would be empty, which seems like a waste, so I used

Oldschool 256B -- Comet Song

I wanted to see if I could get a Mockingboard tune in a 256B demo.

Oldschool 256B -- Orb

This one is really three effects, one that's 128B and two that are roughly 64B. You might think you could save some overhead by combining them, but in reality they don't share much more than the HGR2 call.

The first effect is "Orb" which makes a neat pattern then has a growing multi-colored circle. I came across this by accident when trying to write compact Bresenham circles for hi-res Myst. The initial pattern you get when you draw a circle of radius 0. The weird colors in the growing circles are what happens if you set HCOLORs beyond the 7 that Applesoft allows (basically it indexes into code beyond the color table and uses the bit patterns as colors).

The second effect is a shimmery effect. The occasional static line is actually again indexing out of bounds. Accidental but I left it in because I thought it added character.

The final effect is endless colorful rectangles. This again was something buggy I found working on hi-res Myst. It's decoding 5 bytes as descriptions of how to draw squares, but instead of reading intentional data, it's using random data from the Applesoft ROM.

Finish: 30/32 256 Byte Oldschool Intro
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Oldschool 128B -- Stargate

Flashing light warning.

This one was a buggy result when trying to get some lo-res tunnel drawing code working. This was possibly my favorite entry for Lovebyte, a shame it didn't place better. I tried adding some sound too but wasn't able to get anything that sounded decent. (On Apple II to click the built-in speaker it takes 3 bytes to toggle a memory location. You can get music/sound of a sort if you cycle count things [a stock Apple II has no timers] but it's really hard to get anything more than clicks or static when size coding).

Finish: 11/18 128 Byte Oldschool Intro
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Oldschool 128B -- Rotate

This came out of a bug found when working on the "Thick Sine" demo. I was trying to save space by not setting the carry, and it led to the rippling effect. I realized I could use this plus page flipping to get sort of a log rotating effect. There was also enough room to click the speaker a bit.

Finish: 17/18 Oldschool 128 byte intro
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64B Intro -- dsr64

Using Apple II shape tables / XDRAW to rotate and scale the Desire logo. It also manages to page flip to avoid flicker. The compact page flipping code is in my mind more impressive than the scaled/rotating vector art.

I do lean heavily on these shape table effects in demos because you can get some impressive effects in small size, and scaled vector graphics (in software) are one of the few things the Apple II can do better than other 8-bit machines.

Finish: 4/18 Oldschool 64-byte Intro
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64B Intro -- Thick Sine

Another effect I came across when trying to do something else, in this case I was trying to draw circles. The big challenge here was getting a sine lookup table in a space this small. The Applesoft ROM actually has a cosine table of sorts built in (for use in the shapetable stuff) but it's missing a term. That's why there's a gap in the middle of the sine. It's possible to fix this with another couple of bytes, but I couldn't figure out how to do that and get it to fit under 64B.

Finish: 14/18 Oldschool 64-byte Intro
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32B Intro -- Fuzzball

This one is actually only 29 bytes and I could probably shave a few more bytes off if I set my mind to it.

This is another hi-res shape table thing. Again found by accident. It's walking throuh RAM/ROM a page at a time and using what it finds as a shapetable, rotating by (360/64) degrees each step. Because it's hitting uninitialized RAM, the actual effect you get varies on what kind of RAM you have in your Apple II or emulator.

A simple speaker click in the main loop makes for surprisingly nice sound effects.

Finish: 4/18 Oldschool 32-byte Intro
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CALL -151
E7: 20 D8 F3 C8 84 E7 A0 00 A2 8C A9 60 20 11 F4 2C
F7: 30 C0 A9 00 A8 20 5D F6 E6 FA 4C ED 00
E7G

16B Intro -- Xdraw Wave

Found this while once again searching the Applesoft ROM for a pattern that would make a good shape-table effect. Rotated this time, and it ended up making a nice purple/green effect with the composite artifacts.

The code loads at address $E7 in the zero page, which seems like an odd choice. This is because $E7 is where the ROM looks for the HGR_SCALE value for how big to scale the shapes. By starting our code there that starts with JSR ($20) it sets up the scale to be 32 without us having to do a separate load/store instruction.

Finish: 8/17 16B Oldschool Intro
Download:

CALL -151
E7: 20 D8 F3 AA 20 11 F4 A0 F0 A9 05 20 5D F6 F0 F7
E7G

16B Intro Showcase -- Xdraw Diamond

Another xdraw/shapetable effect. I found this one by accident while trying to save space by making the rotate value be the same as the hi/low address location for the shape table. I actually like this better than the xdraw_wave submission but I had already submitted that one, which is why we ended up with two similar submissions to this competition.

Finish: 6/17 16B Oldschool Intro
Download:

CALL -151
E7: 20 D8 F3 AA 20 11 F4 A9 E7 AA A8 20 5D F6 F0 F7
E7G

8B Intro Showcase -- Tiny Gr

I finally managed an 8B demo that does graphics! This is tricky on the Apple II because setting graphics mode takes 3 bytes, and a loop takes at least 2 bytes, which only would leave 3 bytes for the effect. I was stuck on this for a while, but then I discovered on systems with Applesoft in ROM (which is the majority of Apple IIs you'll come across), at boot the token parsing code is copied to the zero page at address $B1. If you drop your code into the middle of this, you can re-use some of the loop code for free.

In our case, the original loop is incrementing a memory location, loading the value there, doing some stuff, and branching conditionally. We drop in the middle, change the address of the memory access to be further along in RAM (to make it get to the exciting part within the minute deadline), switch to graphics mode, call the character-out routine (which in graphics mode prints/scrolls lo-res graphics) and finally we change the conditional branch to check the overflow flag (which isn't being set, so in effect making it a BRANCH ALWAYS branch).

What this is doing is just reading bytes from RAM and printing them, so the effect will vary based on the RAM in your system. I actually find this recording (on an Apple IIe Platinum) to be a lot more boring than what you get on a II+ which has more stripes. It plays some sound as it hits BEL characters, and then once it hits the $C000 I/O region it clicks through the SPEAKER area, switches to hi-res mode, and then finally crashes.

Finish: 8B showcase, no voting
Download:

CALL -151
B9: 78 2C 50 C0 20 F0 FD 50
B9G