=> {
        panel.innerHTML = '';
        const d = document.createDocumentFragment();

        function project({x, y}) { // -1 ~ 1
          return {
            x: 0.5 * (x + 1) * panel.clientWidth,
            y: 0.5 * (1 - y) * panel.clientHeight,
          };
        }

        let lineWidth = 0,
          color = 'black',
          x0 = 0,
          y0 = 0;

        function line(x1, y1, x2, y2) {
          const div = document.createElement('div');
          div.style.position = 'absolute';
       