This time it wasn't an Amiga demo that triggered the creation of this effect - it was the Super Nintendo Game "Super Castlevania IV"!. A friend of mine had a Super Famicom/ Super Nintendo and lots of games. Super Castlevania IV was one of it.
Tunnel Demo on a green screen
Since he was pretty good at playing all the games on the Super Nintendo he once played the whole game through and I was watching it. Castlevania IV had a lot of cool effects like areas were the whole screen turned around its center point, zooming enemies and backgrounds...
One of the levels started in a tunnel which realistically rotated around the player. To say the least: I was speechless! This tunnel effect looked so cool I just had to try to convert it to the CPC.
I had many ideas how to create it, e.g. by using a single line hardware split, using fast software routines or using a color switch effect... the last method was the first and only I've tried out. (I always wanted to use the hardware line splitting of the CPC+ to create a better version of this routine, but never did!)
Since the CPC doesn't have enough nuances of the same color to satisfy my need for different gradations for the tunnel I used a green screen and the possibility to use all 26 colors as different hues of green to enhance the visual impact of this effect.
The result looked okay, but not really satisfying. I intended to try out the other two possibilities I had in mind, but I was kept busy with other things and never got to work on that again.
Since I used a CRTC register 3 scroll trick for the Terminator scroll and these scrolling tricks always look bad on a green screen I added the rotating Tunnel as special green screen part to the Terminator scroll.
Later I got the idea that I could switch between two or three screens to create the impression of a right or left scrolling tunnel. But this idea also didn't make it into reality. Too bad!