MorphPiece constructor
Creates a plain piece: mass and content, no morph identity.
Implementation
const MorphPiece({
required this.id,
required this.rect,
this.radius = 20,
this.solid = true,
this.bumpScale = 0.6,
this.bumpRecoil = 140,
this.channel,
this.child,
}) : morphable = false;