PIXI兼容微信小游戏

首先导入官方的weapp-adapter，然后导入pixi.min.js，微信小程序使用ES6的module引用模块，具体参见ES6的Module。

import './libs/weapp-adapter';
import * as PIXI from './libs/pixi.min';
const { pixelRatio, windowWidth, windowHeight } = wx.getSystemInfoSync()
let game = new PIXI.Application({
width:windowWidth*pixelRatio,
height:windowHeight*pixelRatio,
view:canvas
});

let graphics = new PIXI.Graphics();
graphics.beginFill(0xfff000);
graphics.lineStyle(0, 0xffffff, 1);
graphics.drawRect(80,80,100,100);
graphics.endFill();
game.stage.addChild(graphics);
let clktext = new PIXI.Text("Click Me!",{fill:"#ffffff",fontSize:32});
clktext.interactive = true;
let times = 0;
clktext.on("pointerdown",()=>{
  clktext.text = `times${++times}`;
});
clktext.x = 200;
clktext.y = 300;
game.stage.addChild(clktext);

目录结构如下

保存运行如下：

完美运行，但是当点击屏幕的任何位置时，报错了，内容如下：

TouchEvent未定义，为什么呢？看pixi源码：

 InteractionManager.prototype.normalizeToPointerData = function normalizeToPointerData(event) {
         var normalizedEvents = [];

         if (this.supportsTouchEvents && event instanceof TouchEvent) {
             for (var i = 0, li = event.changedTouches.length; i < li; i++) {
                 var touch = event.changedTouches[i];

                 if (typeof touch.button === 'undefined') touch.button = event.touches.length ? 1 : 0;
                 if (typeof touch.buttons === 'undefined') touch.buttons = event.touches.length ? 1 : 0;
                 if (typeof touch.isPrimary === 'undefined') {
                     touch.isPrimary = event.touches.length === 1 && event.type === 'touchstart';
                 }
                 if (typeof touch.width === 'undefined') touch.width = touch.radiusX || 1;
                 if (typeof touch.height === 'undefined') touch.height = touch.radiusY || 1;
                 if (typeof touch.tiltX === 'undefined') touch.tiltX = 0;
                 if (typeof touch.tiltY === 'undefined') touch.tiltY = 0;
                 if (typeof touch.pointerType === 'undefined') touch.pointerType = 'touch';
                 if (typeof touch.pointerId === 'undefined') touch.pointerId = touch.identifier || 0;
                 if (typeof touch.pressure === 'undefined') touch.pressure = touch.force || 0.5;
                 touch.twist = 0;
                 touch.tangentialPressure = 0;
                 // TODO: Remove these, as layerX/Y is not a standard, is deprecated, has uneven
                 // support, and the fill ins are not quite the same
                 // offsetX/Y might be okay, but is not the same as clientX/Y when the canvas's top
                 // left is not 0,0 on the page
                 if (typeof touch.layerX === 'undefined') touch.layerX = touch.offsetX = touch.clientX;
                 if (typeof touch.layerY === 'undefined') touch.layerY = touch.offsetY = touch.clientY;

                 // mark the touch as normalized, just so that we know we did it
                 touch.isNormalized = true;

                 normalizedEvents.push(touch);
             }
         }
         // apparently PointerEvent subclasses MouseEvent, so yay
         else if (event instanceof MouseEvent && (!this.supportsPointerEvents || !(event instanceof window.PointerEvent))) {
                 if (typeof event.isPrimary === 'undefined') event.isPrimary = true;
                 if (typeof event.width === 'undefined') event.width = 1;
                 if (typeof event.height === 'undefined') event.height = 1;
                 if (typeof event.tiltX === 'undefined') event.tiltX = 0;
                 if (typeof event.tiltY === 'undefined') event.tiltY = 0;
                 if (typeof event.pointerType === 'undefined') event.pointerType = 'mouse';
                 if (typeof event.pointerId === 'undefined') event.pointerId = MOUSE_POINTER_ID;
                 if (typeof event.pressure === 'undefined') event.pressure = 0.5;
                 event.twist = 0;
                 event.tangentialPressure = 0;

                 // mark the mouse event as normalized, just so that we know we did it
                 event.isNormalized = true;

                 normalizedEvents.push(event);
             } else {
                 normalizedEvents.push(event);
             }

         return normalizedEvents;
     };

第四行判断event是否是TouchEvent类型，报错显示就是TouchEvent未定义，TouchEvent是window的事件类型，打印一下window，发现window里没有TouchEvent属性，所以报错

其实只要把window.TouchEvent暴露出来即可，把weapp-adapter.js源码下载下来，查看源码发现有TouchEvent，但是没有对外导出，导出一下，然后在window.js文件再导出一下，打包一下。

webpack打包一下，替换原来的weapp-adapter.js文件，发现没问题了。但是点击事件出了问题，监听不到了，怎么回事呢？

问题出在事件的点击位置的转换上，pixi源码

InteractionManager.prototype.mapPositionToPoint = function mapPositionToPoint(point, x, y) {
        var rect = void 0;

        // IE 11 fix
        if (!this.interactionDOMElement.parentElement) {
            rect = { x: 0, y: 0, width: 0, height: 0 };
        } else {
            rect = this.interactionDOMElement.getBoundingClientRect();
        }

        var resolutionMultiplier = navigator.isCocoonJS ? this.resolution : 1.0 / this.resolution;

        point.x = (x - rect.left) * (this.interactionDOMElement.width / rect.width) * resolutionMultiplier;
        point.y = (y - rect.top) * (this.interactionDOMElement.height / rect.height) * resolutionMultiplier;
    };

向上追溯源码发现this.interactionDOMElement就是new Application()时传进来的canvas，打印发现就是一个canvas，没有parent。

这个重新映射的原理很简单。简单说就是canvas的尺寸与渲染尺寸。

以iphone5为例，全屏canvas(landscape)大小是568x320而渲染尺寸(devicePixelRatio=2)是1136x640。事件监听捕获到的位置是基于canvas(设备)的，比如有个sprite在屏幕右下角，此时pixi.js获取到的点击坐标是568, 320，而sprite在渲染尺寸的位置是1136, 640，如果不进行正确的映射就无法触发pixi.js内部实现的监听函数。

因为在微信小游戏里canvas肯定是全屏的，所以直接计算position即可

PIXI.interaction.InteractionManager.prototype.mapPositionToPoint = (point, x, y) => {
    point.x = x * pixelRatio
    point.y = y * pixelRatio
}
或者

app.renderer.plugins.interaction.mapPositionToPoint = (point, x, y) => {
    point.x = x * pixelRatio
    point.y = y * pixelRatio
}

再次运行完美！

 还有一个PIXI.loader 和 ajax 相关的问题，

// weapp-adapter 源码
// src/XMLHttpRequest.js
// 添加 addEventListener 方法
addEventListener(ev, cb) {
  this[`on${ev}`] = cb
}

基本完成了。大部分内容来自简书

https://www.jianshu.com/p/38fcbcaf2930，之所以一步步去实现，主要是因为对一些东西还不了解。