text: export class PaperState {
    constructor() {
      if (typeof this.processMouseDown !== 'function') {
        throw "processMouseDown() should be setted";
      }
      if (typeof this.processMouseMove !== 'function') {
        throw "processMouseMove() should be setted";
      }
      if (typeof this.processMouseUp !== 'function') {
        throw "processMouseUp() should be setted";
      }
  
    }
  }