dou_applet/components/echarts/wx-canvas.js

export default class WxCanvas {
  constructor(ctx, canvasId) {
    this.ctx = ctx;
    this.canvasId = canvasId;
    this.chart = null;

    WxCanvas.initStyle(ctx);
    this.initEvent();
  }

  getContext(contextType) {
    return contextType === '2d' ? this.ctx : null;
  }

  setChart(chart) {
    this.chart = chart;
  }

  attachEvent() {
    // noop
  }

  detachEvent() {
    // noop
  }

  static initStyle(ctx) {
    const styles = ['fillStyle', 'strokeStyle', 'globalAlpha',
      'textAlign', 'textBaseAlign', 'shadow', 'lineWidth',
      'lineCap', 'lineJoin', 'lineDash', 'miterLimit', 'fontSize'];

    styles.forEach((style) => {
      Object.defineProperty(ctx, style, {
        set: (value) => {
          if ((style !== 'fillStyle' && style !== 'strokeStyle')
            || (value !== 'none' && value !== null)
          ) {
            ctx[`set${style.charAt(0).toUpperCase()}${style.slice(1)}`](value);
          }
        },
      });
    });

    ctx.createRadialGradient = () => ctx.createCircularGradient(arguments);
  }

  initEvent() {
    this.event = {};
    const eventNames = [{
      wxName: 'touchStart',
      ecName: 'mousedown',
    }, {
      wxName: 'touchMove',
      ecName: 'mousemove',
    }, {
      wxName: 'touchEnd',
      ecName: 'mouseup',
    }, {
      wxName: 'touchEnd',
      ecName: 'click',
    }];

    eventNames.forEach((name) => {
      this.event[name.wxName] = (e) => {
        const touch = e.mp.touches[0];
        this.chart.getZr().handler.dispatch(name.ecName, {
          zrX: name.wxName === 'tap' ? touch.clientX : touch.x,
          zrY: name.wxName === 'tap' ? touch.clientY : touch.y,
        });
      };
    });
  }
}