从今天开始，我们开始正式的学习osg框架，今天我们学习的是osg的渲染模块，我们来看一下代码结构。
所有DrawXXX的js模块都是渲染的模块，我们逐一来简单介绍一下，第一个Drawable.js，这个模块是描述可绘制对象的类，也是我们今天要讨论的类。在osg框架中，渲染管道在准备时期首先要统计管理可绘制对象，我们来看看Drawable模块到底做了什么操作，进行了哪些管理。先贴出代码。
/* 可绘制对象*/ let StateBin = require('./StateBin'); let BoundingBox = require('../util/BoundingBox'); let BoundingSphere = require('../util/BoundingSphere'); let Vec3 = require('../util/Vec3');let Drawable = function (actor) {this._drawActor = actor;//关联的DrawActorthis._geometry = undefined;//渲染的几何Geometrythis._transform = undefined;//世界变换 FloatArray(16)this._statebin = undefined;//状态结点，原始的状态，没有额外功能时的状态this._curStatebin = undefined;//如果状态会动态变化，这里存储每一帧绘制时的状态结点this._depth = 0.0;//场景深度值，透明需要按深度排序绘制this._boundingBox = undefined;//包围盒this._boundingSphere = undefined;//包围球 }; Drawable.prototype = {setGeometry: function (g, transform) {this._geometry = g;this._transform = transform;},getGeometry: function () {return this._geometry;},getTransform: function () {return this._transform;},setStateBin: function (sb) {this._statebin = sb;},getStateBin: function () {return this._statebin;},getCurrentStateBin: function () {return this._curStatebin;},// setDepth: function (d) {// this._depth = d;// },getDepth: function () {return this._depth;},reset: function () {this._geometry = undefined;this._transform = undefined;this._statebin = undefined;this._curStatebin = undefined;this._depth = 0.0;this._boundingBox = undefined;this._boundingSphere = undefined;},valid: function () {if (this._drawActor.getBaseCamera().isBoundingBoxCulled(this.getBoundingBox())) {return false;}return true;},isTransparent: function () {return false;},//计算深度值computeDepth: function () {//根据包围盒和相机变换矩阵，确认中心点的Z值let mvmatrix = this._drawActor.getBaseCamera().getModelViewMatrix();let temp = Vec3.MemoryPool.alloc();this._depth = this.distanceZ(this.getBoundingBox().getCenter(temp), mvmatrix);Vec3.MemoryPool.free(temp);//drawable.setDepth(depth); },//相机的矩阵要取反distanceZ: function (coord, matrix) {return -(coord[0] * matrix[2] + coord[1] * matrix[6] + coord[2] * matrix[10] + matrix[14]);},getBoundingBox: function () {if(this._boundingBox === undefined){this._boundingBox = new BoundingBox();this._boundingBox.copy(this._geometry.getBoundingBox(true));if(this._transform){this._boundingBox.transformMat4(this._transform);}}return this._boundingBox;},getBoundingSphere: function () {if(this._boundingSphere === undefined) {this._boundingSphere = new BoundingSphere();let bb = this.getBoundingBox();this._boundingSphere.expandByBoundingBox(bb);}return this._boundingSphere;},getRadius: function () {return this.getBoundingSphere().getRadius();},// There are 3 cases when there is a prev / current render leaf// pSG: previousStateGraph// cSG: currentStateGraph// pRL: previousRenderLeaf// cRL: currentRenderLeaf// // A B C// +-----+ +-----+ +-----+ +-----+// | pSG | | cSG | +--+ SG +--+ | SG |// +--+--+ +--+--+ | +-----+ | +--+--+// | | | | |// +--v--+ +--v--+ +--v--+ +--v--+ +--v--+// | pSG | | cSG | | pSG | | cSG | +--+ SG +--+// +--+--+ +--+--+ +--+--+ +--+--+ | +-----+ |// | | | | | |// +--v--+ +--v--+ +--v--+ +--v--+ +--v--+ +--v--+// | pRL | | cRL | | pRL | | cRL | | pRL | | cRL |// +-----+ +-----+ +-----+ +-----+ +-----+ +-----+// // // Case A// no common parent StateGraphNode we need to// popStateSet until we find the common parent and then// pushStateSet from the common parent to the current RenderLeaf// // Case B// common parent StateGraphNode so we apply the current stateSet// // Case C// the StateGraphNode is common to the previous RenderLeaf so we dont need// to do anything except if we used an insertStateSetdraw: function (glstate, preDrawable) {//先接受状态，再渲染几何let curStateGraph = this._statebin;let curStateGraphStateSet = curStateGraph.getStateSet();let curStateGraphParent = curStateGraph.getParent();let preStateGraph;let preStateGraphParent;if(preDrawable !== undefined){preStateGraph = preDrawable._statebin;preStateGraphParent = preStateGraph.getParent();if(preStateGraphParent !== curStateGraphParent){//A StateBin.moveStateBin(glstate, preStateGraphParent, curStateGraphParent);glstate.applyStateSet(curStateGraphStateSet);}else if(preStateGraph !== curStateGraph){//B glstate.applyStateSet(curStateGraphStateSet);}else{// in osg we call apply but actually we dont need// except if the stateSetStack changed.// for example if insert/remove StateSet has been used// if (glstate._stateSetStackChanged(idLastDraw, lastStateSetStackSize )) {// glstate.applyStateSet(curStateGraphStateSet);// } }}else{//如果preLeaf为空，第一个绘制的几何，状态遍历到根节点全部push到GLState中 StateBin.moveStateBin(glstate, undefined, curStateGraphParent);glstate.applyStateSet(curStateGraphStateSet);}let camera = this._drawActor.getBaseCamera();glstate.applyModelMatrix(this._transform, camera.getModelViewMatrix(), camera.getProjectionMatrix());this._geometry.draw(glstate);return true;}, }; module.exports = Drawable;// set: function (stateGraph, geometry, , depth) { // this._statebin = stateGraph; // this._geometry = geometry; // // this._depth = depth; // }, // drawGeometry: function (glstate) { // //let program = glstate.getLastProgramApplied(); // //let programID = program.getID(); // //let programCaches = glstate.getProgramCaches(); // //let obj = programCaches[programID]; // // if(!obj){//程序不存在，创建一个新的 // // obj = new CacheUniformApply(glstate, program); // // programCaches[programID] = obj; // // } // // //从相机获取modelview和projection // //着色器暂时不需要透视矩阵 // //let modelview = this._camera.get // // // // //glstate.applyModelViewMatrix(this._modelview); // //glstate.applyProjectionMatrix(this._projection); // glstate.applyTransformMatrix(this._transform); // //this._modelview = this._camera.getModelViewMatrix(); // //Mat4.mul(this._modelview, this._modelview, this._transform); // //this._projection = this._camera.getProjectionMatrix(); // glstate.applyModelMatrix(this._transform, this._camera.getModelViewMatrix(), this._camera.getProjectionMatrix()); // // // //let gluniforms = program.getGLUniformsCache(); // //let modelviewloc = gluniforms[glstate._modelViewMatrixUniform.getName()]; // //let viewloc = gluniforms[glstate._viewMatrixUniform.getName()]; // // //obj.apply(glstate, this._modelview, this._modelworld, this._view, this._projection, this._normal); // this._geometry.draw(glstate); // },
我们先来看看Drawable的构造函数，截取构造函数代码
let Drawable = function (actor) {this._drawActor = actor;//关联的DrawActorthis._geometry = undefined;//渲染的几何Geometrythis._transform = undefined;//世界变换 FloatArray(16)this._statebin = undefined;//状态结点，原始的状态，没有额外功能时的状态this._curStatebin = undefined;//如果状态会动态变化，这里存储每一帧绘制时的状态结点this._depth = 0.0;//场景深度值，透明需要按深度排序绘制this._boundingBox = undefined;//包围盒this._boundingSphere = undefined;//包围球 };
首先我们看到第一个私有属性是DrawActor，我们看看DrawActor是个什么模块，先贴出DrawActor类代码。
/* 绘制对象角色每个DrawActor管理自己的渲染数据，自己的状态树，自己的相机树 如果该功能销毁直接销毁对应的DrawActor资源 但是他引用的状态，相机并不是他管理 不想把各个DrawActor搅和在一起，逻辑混乱绘制分几种情况，全自动，全手动，半自动 全自动-所有的绘制流程从一开始数据构造好后就不会再变更，只需在初始化时确认好 后续直接渲染即可 半自动-部分绘制流程是固定的，部分绘制流程是动态的，比如构件场景下，需要点选高亮等功能变化 全手动-所有的绘制流程都是动态的，每一帧都需要重新构造每个drawable，部分功能数据*/ let Drawable = require('./Drawable'); let StateBin = require('./StateBin'); let NodeVisitor = require('../util/NodeVisitor'); let CullStack = require('./CullStack'); let Mat4 = require('../util/Mat4'); let Group = require('../core/Group'); let Geode = require('../core/Geode'); let MatrixTrasform = require('../core/MatrixTransform'); let SceneRoot = require('../scene/SceneRoot'); let Geometry = require('../core/Geometry');let DrawActor = function (renderer) {NodeVisitor.call(this, NodeVisitor.TRAVERSE_CHILDREN);CullStack.call(this);//为正确渲染准备的数据this._renderer = renderer;//所属的渲染器，固有资产，不会变更this._baseCamera = this._renderer.getMainCamera();//相机，默认为主相机this._baseState = new StateBin();//状态this._sceneRoot = undefined;//所属的场景根节点//渲染的对象this._drawables = [];// this._drawIndex = 0;//当前绘制的索引数，需要固定帧率渲染的地方使用// this._currentStateBin = undefined;//当前处理的状态树结点，临时数据// //this._fixed = false;//是否启用固定帧率this._valid = true;//直接屏蔽渲染的标记 };DrawActor.prototype = Object.create(NodeVisitor.prototype); Object.assign(DrawActor.prototype, CullStack.prototype); DrawActor.prototype.constructor = DrawActor; Object.assign(DrawActor.prototype, {setBaseCamera: function (camera) {//设置当前相机，可以自由设置自己独特的相机this._baseCamera = camera;},getBaseCamera: function () {return this._baseCamera;},getBaseStateBin: function () {return this._baseState;},getBaseStateSet: function () {return this._baseState.getStateSet();},//复原场景根节点的状态revertBaseState: function () {if (this._sceneRoot) {this._baseState.setStateSet(this._sceneRoot.getStateSet());}},//与场景的唯一联系，一定要先定义好场景的几何和状态再调用setSceneRootsetSceneRoot: function (root) {this._sceneRoot = root;//一定要先定义好场景根节点的状态，否则会出错！！！//this._baseState.setStateSet(root.getStateSet()); },createDrawable: function () {//base overridereturn new Drawable(this);//创建对应类型的Drawable },addDrawable: function (drawable) {this._drawables.push(drawable);},getDrawables: function () {return this._drawables;},valid: function (valid) {if (valid !== undefined) {this._valid = valid;}return this._valid;},//遍历apply: function (node) {this[node.typeID](node);},//重载，压入一个状态pushStateSet: function (stateset) {if (stateset) {//添加StateGraph子节点，更新当前活动的StateGraph为新的状态this._currentStateBin = this._currentStateBin.addStateSetChild(stateset);}},//重载，弹出一个状态popStateSet: function (stateset) {if (stateset) {this._currentStateBin = this._currentStateBin.getParent();}},//重载pushDrawable: function (geometry) {let drawable = this.createDrawable();drawable.setStateBin(this._currentStateBin);drawable.setGeometry(geometry, this.getCurrentTransformMatrix());this.addDrawable(drawable);},//根重载，绘制当前Actor下的drawables，绘制不需要固定帧率，永远在第一帧里绘制完毕draw: function (glstate, preCamera) {if (!this._valid) {//不再绘制return preCamera;}this.drawCamera(preCamera);//循环遍历一遍drawables，绘制实体let preDrawable = undefined;let l = this._drawables.length;for (let i = this._drawIndex; i < l; i++) {let drawable = this._drawables[i];if (drawable.valid()) {drawable.draw(glstate, preDrawable);//成功绘制的preDrawable = drawable;}this._drawIndex++;}return this._baseCamera;},//每个新帧绘制之前的重置工作drawReset: function () {this._baseCamera.setClearFlag(false);this._drawIndex = 0;},//当前Actor的对象是否全部绘制完毕drawFinished: function () {return this._drawables.length === this._drawIndex;},//绘制相机状态(视口，清空)drawCamera: function (preCamera) {if (preCamera === this._baseCamera) {//重复的不再处理return;}//视口何时都需要设置let glstate = this._renderer.getGLState();glstate.applyAttribute(this._baseCamera.getViewport());//以下是每个相机只需要处理一次的事情if (!this._baseCamera.getClearFlag()) {//更新视锥体，确保剔除正确，每帧相机的投影矩阵和视图矩阵可能都会变化this._baseCamera.updateCullFrustum();//清空颜色和深度，但如果是主相机不再需要，在最开始就已经清空let clearmask = this._baseCamera.getClearMask();if (clearmask !== 0x0) {let gl = glstate.getWebGLContext();if (clearmask & gl.COLOR_BUFFER_BIT) {let color = this._baseCamera.getClearColor();//清空颜色gl.clearColor(color[0], color[1], color[2], color[3]);}if (clearmask & gl.DEPTH_BUFFER_BIT) {let depth = this._baseCamera.getClearDepth();//清空深度gl.depthMask(true);gl.clearDepth(depth);}gl.clear(clearmask);}this._baseCamera.setClearFlag(true);}},//根重载，线段求交，返回相交的drawable对象linesegmentIntersect: function (start, end, threshold) {let LineSegmentIntersector = require('../util/LineSegmentIntersector');let intersector = new LineSegmentIntersector();intersector.initialize(start, end, threshold);let length = this._drawables.length;for (let i = 0; i < length; i++) {let drawable = this._drawables[i];if (drawable.valid()) {//没有隐藏，没有被剔除的drawable进行相交运算 intersector.intersect(drawable);}}//线段求交结果需要根据ratio排序return intersector.getIntersections();}, });DrawActor.prototype[SceneRoot.typeID] = function (root) {this._baseState.removeChildren();this._baseState.setStateSet(root.getStateSet());this._currentStateBin = this._baseState;this.pushTransformMatrix(root.getRootTransform());//变换矩阵中先推入一个单位矩阵作为根节点，非常重要this.traverse(root);this.popTransformMatrix();this._currentStateBin = undefined; }; DrawActor.prototype[MatrixTrasform.typeID] = function (node) {//模型矩阵变换let lastModelMatrix = this.getCurrentTransformMatrix();let mmatrix = undefined;if (lastModelMatrix) {mmatrix = Mat4.clone(lastModelMatrix);} else {mmatrix = Mat4.new();}node.computeLocalToWorldMatrix(mmatrix);this.pushTransformMatrix(mmatrix);//状态let stateset = node.getStateSet();this.pushStateSet(stateset);this.traverse(node);this.popStateSet(stateset);this.popTransformMatrix(); }; DrawActor.prototype[Geode.typeID] = function (geode) {this[Group.typeID](geode); }; DrawActor.prototype[Group.typeID] = function (group) {let stateset = group.getStateSet();this.pushStateSet(stateset);this.traverse(group);this.popStateSet(stateset); }; DrawActor.prototype[Geometry.typeID] = function (geometry) {//Geometry已经是叶子，不需要继续递归了let stateset = geometry.getStateSet();this.pushStateSet(stateset);this.pushDrawable(geometry);this.popStateSet(stateset); }; module.exports = DrawActor; // reset: function () { // this._drawables.length = 0;//置空 // this._sceneRoot = undefined; // }, // polytopeIntersect: function () { // // }, // sphereIntersect: function () { // // },
我们可以看到，DrawActor是将要被绘制的对象，分成全自动（初始化模型数据就构造Drawable，准备渲染）、半自动（事件触发后构造Drawable，等待渲染）、全手动（用户自己构造Drawable，用户自己将Drawable排入渲染队列）。我们看到，DrawActor的构造函数包含的私有属性有this._renderer渲染器、this._baseCamera待渲染模块所属相机、this._baseState状态（对应shader里的uniform参数）、this._sceneRoot所属场景根节点、this._drawables包含的渲染对象、this._drawIndex当前绘制的索引数（代表本次绘制是第几次绘制，如果一此不能全部绘制完，就分多次绘制，例如模型增长）、this._currentStateBin当前处理的状态树节点、this._valid屏蔽渲染的标记（true：加入渲染队列，false：不加入渲染队列）。
我们再来看看DrawActor的成员函数都做了什么，我们依次来看。
1.setBaseCamera设置参考相机，这就是设置当前绘制对象的观察相机。2.getBaseCamera获取参考相机。3.getbaseStateBin获取状态信息，包括当前渲染对象绑定的shader，uniform参数以及frameBuffer材质。4.getBaseStateSet同样是获取当前渲染对象的状态信息，shader，uniform，材质信息，depth深度缓冲等。5.revertBaseState恢复场景根节点状态，包括shader，uniform参数，材质信息，depth深度缓存。6.setSceneRoot设置场景根节点。7.createDrawable创建渲染对象。8.addDrawable追加渲染对象进入绘制对象数组。9.getDrawable返回渲染对象数组。10.valid标记当前渲染对象是否被屏蔽。11.apply取出每个渲染节点。12.pushStateSet向stateBin中加入stateSet，这里说明一点，stateSet是stateBin的属性。13.popStateSet从stateBin中取出stateSet属性参数。14.pushDrawable创建渲染对象drawable然后加入drawActor的drawable渲染对象数组。15.draw这才是drawActor的核心功能函数，同学们，鲫鱼为大家隆重介绍绘制函数，或者叫渲染函数，这就是将所有的drawable渲染对象进行遍历渲染的功能函数。16.drawReset每一帧绘制之前的整理重置。17.drawFinished判断当前drawActor绘制对象是否全部将drawable数组中的渲染对象绘制完毕。18.drawCamera绘制相机状态（视口，深度缓冲），如果没有渲染对象私有独立的相机，就操作主相机。19.linesegmentIntersection射线碰撞，重载父类方法。
依次看一下上面的函数，我们大致了解了DrawActor类处理的是渲染流程管理的工作。我们接下来继续看Drawable类的其他属性。我们再贴出一次drawable的构造函数。
let Drawable = function (actor) {this._drawActor = actor;//关联的DrawActorthis._geometry = undefined;//渲染的几何Geometrythis._transform = undefined;//世界变换 FloatArray(16)this._statebin = undefined;//状态结点，原始的状态，没有额外功能时的状态this._curStatebin = undefined;//如果状态会动态变化，这里存储每一帧绘制时的状态结点this._depth = 0.0;//场景深度值，透明需要按深度排序绘制this._boundingBox = undefined;//包围盒this._boundingSphere = undefined;//包围球 };
我们已经看过了this._drawActor，也知道了drawActor是管理渲染的类。接下来我们看this._geometry渲染的几何体成员对象。this._transform空间变换矩阵。this._statebin状态节点，用来添加stateSet状态参数对象。this._currStatebin，保存每一帧的临时状态stateSet。this._depth场景深度值，作用于主相机或渲染对象私有相机（如果有私有相机的话）。this._boundingBox包围盒。this._boundingSphere包围球。这些就是Drawable类的成员。我们马上来看一下Drawable的成员函数。
Drawable成员函数。贴出代码。
setGeometry: function (g, transform) {this._geometry = g;this._transform = transform;},getGeometry: function () {return this._geometry;},getTransform: function () {return this._transform;},setStateBin: function (sb) {this._statebin = sb;},getStateBin: function () {return this._statebin;},getCurrentStateBin: function () {return this._curStatebin;},// setDepth: function (d) {// this._depth = d;// },getDepth: function () {return this._depth;},reset: function () {this._geometry = undefined;this._transform = undefined;this._statebin = undefined;this._curStatebin = undefined;this._depth = 0.0;this._boundingBox = undefined;this._boundingSphere = undefined;},valid: function () {if (this._drawActor.getBaseCamera().isBoundingBoxCulled(this.getBoundingBox())) {return false;}return true;},isTransparent: function () {return false;},//计算深度值computeDepth: function () {//根据包围盒和相机变换矩阵，确认中心点的Z值let mvmatrix = this._drawActor.getBaseCamera().getModelViewMatrix();let temp = Vec3.MemoryPool.alloc();this._depth = this.distanceZ(this.getBoundingBox().getCenter(temp), mvmatrix);Vec3.MemoryPool.free(temp);//drawable.setDepth(depth); },//相机的矩阵要取反distanceZ: function (coord, matrix) {return -(coord[0] * matrix[2] + coord[1] * matrix[6] + coord[2] * matrix[10] + matrix[14]);},getBoundingBox: function () {if(this._boundingBox === undefined){this._boundingBox = new BoundingBox();this._boundingBox.copy(this._geometry.getBoundingBox(true));if(this._transform){this._boundingBox.transformMat4(this._transform);}}return this._boundingBox;},getBoundingSphere: function () {if(this._boundingSphere === undefined) {this._boundingSphere = new BoundingSphere();let bb = this.getBoundingBox();this._boundingSphere.expandByBoundingBox(bb);}return this._boundingSphere;},getRadius: function () {return this.getBoundingSphere().getRadius();},
都是设置和获取属性的函数，包括包围盒和包围球。接下来我们来看看最核心的部分，隆重介绍draw绘制函数，请看代码。
// There are 3 cases when there is a prev / current render leaf// pSG: previousStateGraph// cSG: currentStateGraph// pRL: previousRenderLeaf// cRL: currentRenderLeaf// // A B C// +-----+ +-----+ +-----+ +-----+// | pSG | | cSG | +--+ SG +--+ | SG |// +--+--+ +--+--+ | +-----+ | +--+--+// | | | | |// +--v--+ +--v--+ +--v--+ +--v--+ +--v--+// | pSG | | cSG | | pSG | | cSG | +--+ SG +--+// +--+--+ +--+--+ +--+--+ +--+--+ | +-----+ |// | | | | | |// +--v--+ +--v--+ +--v--+ +--v--+ +--v--+ +--v--+// | pRL | | cRL | | pRL | | cRL | | pRL | | cRL |// +-----+ +-----+ +-----+ +-----+ +-----+ +-----+// // // Case A// no common parent StateGraphNode we need to// popStateSet until we find the common parent and then// pushStateSet from the common parent to the current RenderLeaf// // Case B// common parent StateGraphNode so we apply the current stateSet// // Case C// the StateGraphNode is common to the previous RenderLeaf so we dont need// to do anything except if we used an insertStateSetdraw: function (glstate, preDrawable) {//先接受状态，再渲染几何let curStateGraph = this._statebin;let curStateGraphStateSet = curStateGraph.getStateSet();let curStateGraphParent = curStateGraph.getParent();let preStateGraph;let preStateGraphParent;if(preDrawable !== undefined){preStateGraph = preDrawable._statebin;preStateGraphParent = preStateGraph.getParent();if(preStateGraphParent !== curStateGraphParent){//A StateBin.moveStateBin(glstate, preStateGraphParent, curStateGraphParent);glstate.applyStateSet(curStateGraphStateSet);}else if(preStateGraph !== curStateGraph){//B glstate.applyStateSet(curStateGraphStateSet);}else{// in osg we call apply but actually we dont need// except if the stateSetStack changed.// for example if insert/remove StateSet has been used// if (glstate._stateSetStackChanged(idLastDraw, lastStateSetStackSize )) {// glstate.applyStateSet(curStateGraphStateSet);// } }}else{//如果preLeaf为空，第一个绘制的几何，状态遍历到根节点全部push到GLState中 StateBin.moveStateBin(glstate, undefined, curStateGraphParent);glstate.applyStateSet(curStateGraphStateSet);}let camera = this._drawActor.getBaseCamera();glstate.applyModelMatrix(this._transform, camera.getModelViewMatrix(), camera.getProjectionMatrix());this._geometry.draw(glstate);return true;},
我将注释也贴了出来，我们可以看到，渲染绘制是分三种情况的，首先我们要了解一下StateGraph渲染属性这个来源于osg的概念。stateGraph是渲染的状态属性，包括本次渲染绑定的shader，uniform参数，frameBuffer材质属性，depth深度属性。好了，大致了解了StateGraph后我们再来了解一下RenderLeaf渲染叶这个同样来自osg的概念。RenderLeaf是渲染叶，需要注意的是渲染叶保存的是sceneTree的节点状态，而不是场景树的几何和transform信息。好了，了解了这两个概念我们来看看这三种情况。A.前一帧stateGraph和后一帧stateGraph没有同一个父节点；B.前后两帧stateGraph有同一个父节点；C.前后两帧renderLeaf有共同父节点。针对这三种情况，处理的方式不同，需要注意。鲫鱼也才开始逐步研究osg框架，理解不到位之处请各位方家海涵。
好了，今天讲述的是osg的渲染模块中的一部分DrawActor和Drawable两个模块。下一篇会进一步讲述渲染模块。欢迎大家讨论，祝大家元旦快乐。本文系原创，如需引用，请注明出处：https://www.cnblogs.com/ccentry/p/10199157.html
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