Bad Apple

Bad Apple is a popular Japanese shadow-art animation video that runs as a demo on many computer platforms. This is another version for the TI-99/4A home computer.

Screenshots

You can watch the full video on Youtube.

Features

• Data: 4.5 MB in cartridge ROM.
• Player code: 394 bytes of assembly (TMS990 processor).
• Animation: 256x192 pixels at 25 fps or 30 fps (TMS9918 video processor).
• Sound: chiptune at 50 fps or 60 fps (TMS9919/SN76489 sound processor).
• Vocals: linear predictive coding at 40 fps (TMS5200 speech synthesizer).

Requirements

• TI-99/4A home computer.
• A programmable cartridge with at least 4.5 MB of ROM/RAM.

or:

• An emulator for the TI-99/4A, such as Mame.

Downloading

You can download the latest binary from Github.

Building

If you want to build the demo yourself, you'll need a couple of tools. These are readily available for Linux distributions, but other platforms should work as well.

• A Java runtime environment, version 14 or higher, for the video tools.
• The ImageMagick image toolkit (Debian package imagemagick), for creating the titles.
• The ffmpeg video converter (Debian package ffmpeg), for extracting the video frames.
• The sox sound tool (Debian package sox), for converting the speech audio files.
• My video tools for the TI-99/4A, for computing the speech coefficients and for tying the animation, music, and vocals together.
• The xdt99 cross-development tools, for assembling the final video player.

You'll need to download the data files manually:

• The video as data/BadApple.webm.
• The music as data/BadAppleMusic.vgm.
• The vocals as data/BadAppleVocals.wav.

On Linux, you can then run the build script. Building for a European 50Hz PAL system (the default):

./build.sh pal

or building for a US 60Hz NTSC system:

./build.sh ntsc

Alternatively, you can run its commands manually.

You'll then have

• a raw cartridge ROM file out/romc.bin.
• a cartridge file out/BadApple.rpk that is suitable for emulators like Mame.

Running

The easiest way is to use the Mame emulator (version 0.243 or higher).

On Linux, you can run the script to launch Mame with the proper options. Emulating a European 50Hz PAL system (the default):

./run.sh pal

or emulating a US 60Hz NTSC system:

./run.sh ntsc

Alternatively, you can run the Mame command manually.

Once Mame is running and showing the TI-99/4A home screen:

1. Press any key.
2. Press 2 for "BAD APPLE" or 3 for "BAD APPLE WITH VOCALS".

You can exit Mame by pressing Insert and then Esc.

Implementation

I have created an optimized video format and a video player that essentially send streams of bytes to the video processor (TMS9918), the sound processor (TMS9919/SN76489), and the speech synthesizer (TMS5200). The project grew to the point that the video tools are now a separate project. The tools are more generally useful for creating and playing videos on the TI-99/4A.

The animation of Bad Apple has been sampled down to 256x192 monochrome pixels at 25 Hz. The video tools compress them losslessly. The player runs in bitmap mode. It updates the necessary characters in the screen image table of 32x24 characters and their corresponding patterns of 8x8 pixels each, in the pattern definition table. Since the video is monochrome (except for the postcredits), it doesn't need to update the color definition table, which keeps the frame rate sufficiently high.

The music was available as a chiptune at 50 fps, in VGM format. The video tools convert and simplify those data to streams of data for the sound processor.

The vocals were available as a sound file. I've converted them to linear predictive coding (LPC) speech coefficients at 40 fps, using the my own ConvertWavToLpcd tool from the video tools. It computes and quantizes the coefficients specifically for the speech synthesizer. The sound file has a lot of echo/reverb/overdub, which makes it particularly hard to analyze and convert. After a lot of tweaking, the current final result is fair.

Other versions

The animation is a hallmark test for retrocomputing. These are many versions for platforms from the 1980s.

Computer	Developer	Video	Processor	Video processor	Sound processor	Video performance	Sound performance
TI-99/4A	Tursi	video	TMS9900 @ 3 MHz	TMS9918	TMS9919	192x128 pixels @ 16 fps	PCM @ 13.8 kHz
TI-99/4A	Asmusr		TMS9900 @ 3 MHz	TMS9918	TMS9919	VQ @ 15 fps	/
TI-99/4A	Eric Lafortune		TMS9900 @ 3 MHz	TMS9918	TMS9919 + TMS5200	256x192 pixels @ 25 fps	Chiptune + vocals
ZX Spectrum	?	video	Z80 @ 3.5 MHZ	ULA	2 x AY/YM	256×192 pixels
C64	Algorithm / Onslaught	video	6510 @ 1 MHz	VIC-II	SID 6581	VQ @ 12 fps	Chiptune
MSX1	Pyhesti	video	Z80 @ 3.5 MHz	TMS9918	AY-3-8910	VQ	Chiptune
MSX TurboR	Ryun	video	Z80 @ 3.5 MHz	TMS9958	AY-3-8910	256x192 pixels @ 30 fps	PCM @ 15.75 kHz
MSX TurboR	Yeongman Seo	video	Z80 @ 3.5 MHz	TMS9958	AY-3-8910	256x192 pixels @ 12 fps	PCM @ 11 kHz
BBC Micro	Bitshifters	video	6502 @ 2MHz	SAA5050	SN76489	40x25 chars @ 25 fps	Chiptune @ 50 fps
Intellivision	Decle	video	CP1610 @ 895 kHz	AY-3-8900-1	AY-3-8914	80x48 pixels @ 30 fps
Sega Master System	Psidum et al.	video	Z80 @ 3.59 MHz	YM2602	SN76489	256x192 pixels @ 25 fps
Sega Megadrive	?	video	68000 @ 7.6 MHz	YM7101	YM2612	320x224 pixels @ 30 fps	ADPCM @ 13 kHz
NEC PC-6601	タイニーP	video	Z80 @ 4 MHz	ìPD8049	AY-3-8910 + µPD7752	256x192 pixels @ 9 fps	Chiptune + vocals

The demos all have different strengths. Versions with PCM audio render the original music and audio. Also notably, the BBC Micro version and the C64 version run off floppy disks!

Acknowledgements

Team Shanghai Alice developed the orginal video game Touhou. Masayoshi Minoshima and Nomico created a remix of the music. A collaborative group led by Anira created the video.

Inverse Phase composed the chiptune, originally for the demo on the BBC Micro version.

Secondary German extracted an acapella version of the song (video, audio).

License

This Bad Apple demo for the TI-99/4A is released under the GNU General Public License, version 2.

Enjoy!

Eric Lafortune