MirrorGrid constructor
defaultFg/defaultBg fill empty/newly-grown cells. They must match the
engine's blank-cell colors (the configured default fg/bg) so untouched rows
— which the engine never sends partial damage for — render in the right
color from the first frame instead of a stale hardcoded default.
Implementation
MirrorGrid({int defaultFg = 0xD8D8D8, int defaultBg = 0x181818})
: _defaultFg = defaultFg,
_defaultBg = defaultBg;