Interface SpriteGroupMember

Anything a SpriteGroup can gate: a position in the world units the camera sees, and a per-frame advance. Both AnimatedSprite and ParticleEmitter satisfy this structurally, so a crowd of goblins and the campfire between them can share one group.

interface SpriteGroupMember {
    x: number;
    y: number;
    update(dt: number): void;
}