This is a "bitmap effect", e.g. a visually enhanced appearing of image.
Originally, I've written it in 1997 in Assembler (under Eclipse E.O.S) and C (Watcom). The generation of the plasma and computation of the shading was done by a Turbo Pascal program.
Then in 1999, I've "ported" it under nasm for Linux/x86, using OpenPTC as the graphical library.
Then in 2001, since OpenPTC is dead, it uses SDL. To change the resolution from 320x200 to 640x480 I had to:
Originally, I wanted to use this graphical effect in Frozen-Bubble, for transitions between levels; but since it would appear to be too slow for lower-end machines, Frozen-Bubble contains simpler graphical effects (plasma-ordered fill, random points, horizontal blinds, vertical blinds, center=>edge circle, up=>down bars, top-left=>bottom-right squares).