Fade
Fade
Generic fade effect — takes a symbol and oscillates its foreground color
from its original color toward the terrain background (or BLACK if there
is none) over 10 frames, then completes. Mirrors Java's Fade, which
recomputes Util.oscillate(bg, symbol.getColor(outside), 10, frame) each
tick rather than stepping through a fixed set of frames.
Used for death animations and teleportation.
An optional onComplete callback is invoked when the animation finishes.