This is a demo - not a POC for a game. A game with such quality (on sound and parallax scrollings) is not possible.
Part of the demo is cheating.
Think about it: a small one-screen intro... on a 512KB cardridge!?
As the best example, all played notes from the original MOD were generated and saved to rom: 368KB!
More than 1/3 of cputime during the show is spent by copying samples from rom to ram to be played.
Others cheats are: 52KB (out of 64KB) ram dedicated to screen (incl. 16KB just for the small wall scroll at bottom),
generated code in rom for balloons and moon, generated code for delta-packing animations in sprite,...
512KB were full quickly!
Part of the demo is not cheating.
From the nfo: promote Amstrad GX4000 as one of the most powerful 8bit platforms.
That's it: GX4000 is just too powerful!
There's no cheat there, I'm using standard features from the hardware:
* dma-AY on 3 channels
* 4096 colors - palette: 16 for background + 15 for sprites
* colorful sprites - which are zoom-able (watch those trees)
* 1-pixel H/V scroll
* splitscreens & programmable scanline interruptions
From the nfo again: that's an easy job to show that GX4000 is not the crap most of people were lauhging at.