NN2022100801/addons/admin/node_modules/@antv/f2/es/graphic/engine/canvas-element.js

import EventEmit from '../event/emit';

class CanvasElement extends EventEmit {
  constructor(ctx) {
    super();
    this.context = ctx; // canvas实际的宽高 (width/height) * pixelRatio

    this.width = 0;
    this.height = 0;
    this.style = {};
    this.currentStyle = {};
    this.attrs = {}; // 用来标识是CanvasElement实例

    this.isCanvasElement = true;
  }

  getContext()
  /* type */
  {
    return this.context;
  }

  getBoundingClientRect() {
    var width = this.width;
    var height = this.height; // 默认都处理成可视窗口的顶部位置

    return {
      top: 0,
      right: width,
      bottom: height,
      left: 0
    };
  }

  setAttribute(key, value) {
    this.attrs[key] = value;
  }

  addEventListener(type, listener) {
    this.on(type, listener);
  }

  removeEventListener(type, listener) {
    this.off(type, listener);
  }

  dispatchEvent(type, e) {
    this.emit(type, e);
  }

}

function supportEventListener(canvas) {
  if (!canvas) {
    return false;
  } // 非 HTMLCanvasElement


  if (canvas.nodeType !== 1 || !canvas.nodeName || canvas.nodeName.toLowerCase() !== 'canvas') {
    return false;
  } // 微信小程序canvas.getContext('2d')时也是CanvasRenderingContext2D
  // 也会有ctx.canvas, 而且nodeType也是1，所以还要在看下是否支持addEventListener


  var support = false;

  try {
    canvas.addEventListener('eventTest', function () {
      support = true;
    });
    canvas.dispatchEvent(new Event('eventTest'));
  } catch (error) {
    support = false;
  }

  return support;
}

export default {
  create(ctx) {
    if (!ctx) {
      return null;
    }

    if (supportEventListener(ctx.canvas)) {
      return ctx.canvas;
    }

    return new CanvasElement(ctx);
  }

};