"Rewind 2" for the Apple IIe

Details

Video

System Requirements

• An Apple IIe with 128k RAM and Mockingboard
• It might work on a IIgs with Mockingboard
• It also might work on a IIc with Mockingboard, but the graphics won't be smooth because I don't have IIc VBLANK code that works when the Mockingboard is generating interrupts.

Downloads

Disk Images

• This is version 1.0 (26 March 2025) rewind2.dsk (140k)
  
• If you don't have real hardware it should work in emulators. Applewin (be sure to enable mockingboard sound support) and MAME both tested.
• Try it on the in-browser emulator at archive.org

Source

• You can find it in the full git repository here: You'll need cc65 to build it.
  https://github.com/deater/dos33fsprogs/demos/rewind2

Mini-faq

• Q. Why are there not many questions here yet?
  
  A. It's a busy time of year.
  
  
• Q. Can you tell me more about AUX memory and the Apple IIe double resolution modes?
  
  A. I have a writeup that I will link here when I finish.
  
  

Code Notes

Overall Framework

Effects summary

Multi-color image transition	Having one image for each color would take up too much RAM. Wrote a converter that takes a 4-color image, packs it to 4 pixels per byte, then decompresses and changing color on the fly. That sounds overly-complex you might say. Why not take a regular image and do a search/replace on the colors? Well haha let me tell you about Apple II double-hires. It packs 7 pixels across 4 bytes, with half of those bytes in a different (AUX) memory bank. So search/replace would be an intense amount of shifting/masking/etc. It's bad enough as it is, and when I modified it to use page-flipping it became even more inefficient as I had to swap banks essentially every other pixel. It turned out nice, but it's slow, and even after a lot of cycle-optimizing work it's at least 2 seconds to decompress each frame. Why not just decompress once for each color and copy? Well double hi-res image is 16k, page-flipping means another 16k, you rapidly run out of RAM at that rate. And we can't load from disk while the music is playing.
Scrolling Headphones	The tricky part here was the double-hires scroll across both memory pages (because again we are doing page flipping). Since this is Apple II there's no hardware accelerating of this, you have to manually copy 16k of data each step. (And since we are page flipping it means you actually scroll by 2 lines on alternating pages which gets a bit tricky). The AUX memory layout is a pain so for some of these things I put the code that needs to manipulate both AUX and MAIN up in the language card area with the sound player code. That way it can STA to RDAUX/WRAUX/RDMAIN/WRMAIN with impunity from up there without the executing code being swapped out from under.
Animated tape deck	This is just decompressing the three frames, nothing fancy. Well besides having to handle the page flipping. We also wait for VBLANK which is also fun as Apple IIe/IIc/IIgs all have different ways of doing it, and on IIc it requires messing with firmware interrupts (so we don't handle IIc right now)
Dancing Lady	This is in double lo-res mode. Uses page-flipping. This turned out to be easier than expected. Was going to go through all the trouble of having the parallax scrolling and double lores software sprites, only to realize it's only 24 frames of animation total and there's room to just decompress to memory and copy them over as needed. It compresses *really* well because of all the repetition.

Development Notes