Introduction:
After the release of my very first Apple II intro at Kansasfest 2023, I straight on continued AppleII coding and created a few very smaller non-realtime effects to be released towards the tail-end of 2023. Hoping to keep my newly minted Apple II knowledge fresh.
However other projects took over soon after and when Kansasfest 2024 came around, I hadn't touched the Apple II in almost a year :D Time to get busy again!
Development:
Most of getting to know the platforms and research on the "Double-Dither" screenmode was done the previous year during the development of Overboard (2023). Basically the double-dither mode sets up a 2x2 ditherpattern between any of the 15-colors available in LORES Apple II mode by using 80-columns mode in an interesting way. You can read all about the specifics about this videomode here.
For the intro effect itself, I was trying to go for a variation on the trigonometry-free tunnel that I had designed for Venturo on the Atari ST back in 2022. Since the setup and overhead already took quite a chunk out of the size-budget I was betting that calculating this kind of shape would be possible on a smaller sizebudget (around 160 bytes).
Here is a step by step for the calculations:
* Calculate Absolute Centerpoint X and mirrored AY coordinate ( ax=abs(x-20) ay=(y-22) )
* Calculate UZ space that is bended 45 degrees ( U=ax-ay Z=ax+ay )
* Calculate Final UV values ( X=(U*4)/Z Y=127/Z ) using a custom taylored division routine
* Calculate Final Color Texture using binary operation( color = (X&Y) )
* Transform the Colorindex value over time for masking different parts in and out
* Lookup the final colorindex in the Double-Dither color-lookup tables.
With this, The intro was polished, finished and delivered just in time for release at Kansasfest 2024.
Conclusion:
Getting this intro done was a hard one, mainly due to lack of motivation for doing demoscene stuff. But as I promised the folks at Kansasfest and myself a new demoscene release I mustered just about enough energy to get this thing released. And for the platform and size I think it turned out nicely.
For more information, you can check out the intro at demozoo: Datura (2024)