That's a pretty nice effect, totally possible on the PCE/Turbo. But what's hard to tell from the video is whether it's really transparent. It looks to me like it's alternating between the static BG and the warped BG 60 times a second. When there's that slowdown, the alternation slows down as well.
I wouldn't call it "transparent" therefore.
Of course its not a 'true' transparency, thats why I call it an 'effect'.
And yes, it is alternating between two bgs, which I think is pretty impressive considering what they're doing.
It looks best seeing it on real hardware, but it turns out great in Magic Engine too.
There are also a bunch of space bgs that don't warp, but scroll seperately. They're also cool, but the warping bg is what always stood out most for me.
I have never ever ever witnessed any slowdown in Vasteel whatsoever...and I've played through it dozens of times, both characters, on every possible battlefield. Never come across even a second of slowdown at all. I always thought it was awesome that it had zero slowdown.
The way I remember it, there were times when I'd be running from a diagonal lazer and it'd slowdown slightly. But its been a while so maybe I'm mixing memories with another game.
There's definitely some big flicker in a couple spots, like the base with the foreground columns. But overall it runs perfectly almost everywhere.