Skip to content

Latest commit

 

History

History
76 lines (58 loc) · 3.43 KB

README.md

File metadata and controls

76 lines (58 loc) · 3.43 KB
Raw

Bad Apple Demo

This demo is the classic Bad Apple demo or "how to fit a 3min video on a CPU absolutely not made for that". Watch it on YouTube

How to run

Download the release.

Open BAD_DATA.DSK file in your favourite emulator (I tested Mame and AppleWin). It will run automatically. When requested to flip the disk, insert BAD_APPLE_DATA.DSK in the same drive. Hit enter, and enjoy !

Background information

I decided to do it after watching the demo from Onslaught on C64. It sounded sad to me that the Apple didn't run the Bad Apple :-)

It was made specifically for the Apple ][+ with floppy disk because that's the computer I had when I was a kid. I also chose that machine because of its hardware limitations.

For those interested, my code is here, "as is".

Compression

If you're really interested, look at the kmean.py file. That's the compressor. This is what it does:

  1. drop some frames in the original video (chosen wisely)
  2. compute the delta between each frame, let's call that d-frames
  3. cut each d-frame in tiles of 8x8 pixels
  4. reduce the set of all tiles of all d-frames using k-means approach (basic Lloyd algorithm + euclidean distance; now that I think about it, euclidean distance may be replaced with IoU distance, could be better)
  5. use a form of RLE encoding to compress each run of tiles in d-frame (this gives "stripes")
  6. use a Huffman style dictionary to compress each stripe. Huffman is not practical on low performance machines, so I had to make an "approximation" to reach a better speed/compression balance.
  7. store the data on the disk (regular Prodos sectors, not a file)

Steps 4 and 6 are clearly the more sophisticated ones.

The code is not super optimized and neither is the compressor. Giving it more time, I think I could improve some more the screen size of the video. For example, I have the impression that using 16x16 tiles might be more efficient, but in that case, the k-means approach must be tuned some more.

Decompression

The decompressor is, of course written in assembler (6502 is 1MHz).

It has several gotcha's:

  • The Apple 2 has no timer. So if one wants to play a video at constant speed, one has to figure out a time base. For that I use the rotation speed of the disk drive. How clever :-)
  • The Apple 2 has no graphics CPU, no tricks whatsoever to accelerate drawing so one has to move memory a lot, which affect performance a lot.
  • Reading disk sectors is CPU blocking, so I have to read sectors out of order and mix reading and drawing on the screen in a way that the animation has no hiccup's.
  • Huffman decompression is quite tricky, I've spent a lot of time to get it to work and fast enough.
  • I need most of the memory to store Huffman's table and 8x8 tiles. So I have to remove Prodos (fortunately, I could find RWTS routines source code)

If you ever have the opportunity to run it on real Apple, please send me a video. That would be a very much apprciated gift. It works on real hardware !

For those old enough and in the specific niche, I used to be called The Wizard of the Imphobia group. By that time it was customary to send some greetings, so greetings to Scorpio, PL, Darkness, the Overseas team, my family,...