pause property

ValueNotifier<bool> pause

@en: control the game pause through external means.
Suitable for creating multiple flutter_graph_widget
and keeping alive without causing the game engine to consume too much computation

@zh: 从外部决定游戏是否暂停
适用于创建了多个 flutter_graph_widget，
并且 keepAlive 的情况下，又不想让游戏引擎占用过高计算量

Implementation

ValueNotifier<bool> pause = ValueNotifier(false);