WebGL------osg框架学习二

　　今天我们继续来学习osg.js框架。上一篇我们介绍了DrawActor对象绘制操作类和Drawable可绘制对象类，我们大致知道了osg对Drawable可绘制对象的绘制流程管理。今天我们要继续介绍StateBin状态树节点类。我们来看一下StateBin，他管理的是StateSet状态，他将每个模型节点的StateSet状态信息（shaderLink，材质，depth等）包装成树节点，从而能够将状态节点递归组装成一棵状态树。我们来看看StateBin的构造函数。

/*
状态树结点
保存一个StateSet,每个StateSet都有一个唯一ID
 */
//let MemoryPool = require('../util/MemoryPool');

let StateBin = function () {
    this._stateset = undefined;
    this._parent = undefined;//StateBin
    this._children = {};//属性名为StateSet的ID，值为StateBin
    //this._children._keys = [];//StateSet的ID
    this._depth = 0;//树的深度值
};

　　首先我们可以看到StateBin的成员，this._stateset这就是模型节点的状态信息（shaderLink，材质，depth），this._parent该树节点的父节点，this._children该树节点的子节点，this._depth树的深度。这是一个典型的树节点类，熟悉数据结构的同学都明白如何递归构造一棵树，鲫鱼就不再啰嗦了。我们接下来看看StateBin的成员函数有哪些。

StateBin.prototype = {
    getStateSet: function () {
        return this._stateset;
    },
    setStateSet: function (s) {
        this._stateset = s;
    },
    getParent: function () {
        return this._parent;
    },
    reset: function () {//重置数据，一般都是根节点调用
        this._stateset = undefined;
        this._parent = undefined;

        //之所以遍历是为了StateGraph不被析构以内存复用，而不是每次都重新创建
        //然后是StateGraph的数据必须被清空，重新使用时不会出错
        // let keys = this._children.keys();
        // let l = keys.length;
        // for (let i = 0; i < l; i++) {
        //     let key = keys[i];
        //     let child = this._children[key];
        //     child.reset();
        //     //内存池
        //     //MemoryPool.StateBin.put(child);
        // }
        this._children = {};
        //this._children._keys.length = 0;
        //this._children._keys = [];
        this._depth = 0;
    },
    addStateBinChild: function (bin) {
        bin._parent = this;
        bin._depth = this._depth + 1;
        let id = bin._stateset.getID();
        this._children[id] = bin;
    },
    addStateSetChild: function (stateset) {//添加子节点，以stateset的id为key，返回新创建或者已经存在的StateBin
        let id = stateset.getID();
        let child = this._children[id];
        if (child) {
            return child;
        } else {
            let sg = new StateBin();
            //let sg = MemoryPool.StateBin.get();
            sg._parent = this;
            sg._depth = this._depth + 1;
            sg._stateset = stateset;
            this._children[id] = sg;
            //children._keys.push(id);
            return sg;
        }
    },
    removeStateBinChild: function (bin) {
        let id = bin._stateset.getID();
        let cbin = this._children[id];
        if (cbin) {
            cbin.parent = undefined;
            delete this._children[id];
        }
    },
    removeStateSetChild: function (stateset) {
        let id = stateset.getID();
        let cbin = this._children[id];
        if (cbin) {
            cbin.parent = undefined;
            delete this._children[id];
        }
    },
    removeChildren: function () {
        this._children = {};
    },
};

我们一个一个来看，getStateSet获取当前树节点的渲染状态信息this._stateset；setStateSet设置当前树节点的渲染状态信息即修改this._stateset；getParent获取当前树节点的父节点；reset初始化节点数据，将节点属性清空析构；addStateBinChild向当前树节点中加入一个子节点；addStateSetChild如果当前树节点存在id是stateset的id的子节点，就返回该子节点，如果不存在就创建一个stateset状态的子节点并返回；removeStateBinChild删除当前节点的确定id的某个子节点；removeStateSetChild删除当前节点某个状态是stateset的子节点；removeChildren删除该树节点的所有子节点。

　　我们可以清楚的看到，成员函数基本都是对树结构的操作，最后还有一个方法是对父状态的遍历继承，我们来看一下。

//父状态的匹配
StateBin.moveStateBin = function (glstate, preStateBin, curStateBin) {
    if (curStateBin === preStateBin) {//两个相同什么都不做
        return;
    }

    if (curStateBin === undefined) {
        //curStateBin已经到顶，弹出preStateBin的所有状态
        do {
            if (preStateBin._stateset !== undefined) {
                glstate.popStateSet();
            }
            preStateBin = preStateBin._parent;
        } while (preStateBin);
        return;
    }

    if (preStateBin === undefined) {
        //preStateBin已经到顶，压入curStateBin的所有状态
        //从子节点往根节点遍历获取所有的状态，但是推给glstate必须从根节点往子节点遍历
        //所以这里先塞到一个stack里面，然后再遍历stack推给glstate
        let stack = [];
        do {
            if (curStateBin._stateset !== undefined) {
                stack.push(curStateBin._stateset);
            }
            curStateBin = curStateBin._parent;
        } while (curStateBin);

        let size = stack.length - 1;
        for (let i = size; i >= 0; --i) {
            glstate.pushStateSet(stack[i]);
        }
        return;
    } else if (preStateBin._parent === curStateBin._parent) {
        // first handle the typical case which is two glstate groups
        // are neighbours.

        // glstate has changed so need to pop old glstate.
        if (preStateBin._stateset !== undefined) {
            glstate.popStateSet();
        }
        // and push new glstate.
        if (curStateBin._stateset !== undefined) {
            glstate.pushStateSet(curStateBin._stateset);
        }
        return;
    }

    //先弹出状态，保证preStateBin和curStateBin达到树节点平级
    //无法确定两个树节点谁的深度值更多，两个都做一次循环
    while (preStateBin._depth > curStateBin._depth) {
        if (preStateBin._stateset !== undefined) {
            glstate.popStateSet();
        }
        preStateBin = preStateBin._parent;
    }

    // use return path to trace back steps to curStateBin.
    let stack = [];
    // need to pop back up to the same depth as the curr glstate group.
    while (curStateBin._depth > preStateBin._depth) {
        if (curStateBin._stateset !== undefined) {
            stack.push(curStateBin._stateset);
        }
        curStateBin = curStateBin._parent;
    }

    // now pop back up both parent paths until they agree.
    // should be this to conform with above case where two StateBin
    // nodes have the same parent
    //继续遍历直到两个树节点相同
    while (preStateBin !== curStateBin) {
        if (preStateBin._stateset !== undefined) {//pre的从GLState中出栈
            glstate.popStateSet();
        }
        preStateBin = preStateBin._parent;

        if (curStateBin._stateset !== undefined) {//当前的入栈，临时保存
            stack.push(curStateBin._stateset);
        }
        curStateBin = curStateBin._parent;
    }

    //遍历结束后，从临时栈中推入GLState里
    for (let i = stack.length - 1, l = 0; i >= l; --i) {
        glstate.pushStateSet(stack[i]);
    }
};

这段代码我们仔细来看一下。

第一件事比较当前节点状态和前一个节点状态，相同则直接返回。

if (curStateBin === preStateBin) {//两个相同什么都不做
        return;
    }

接下来如果前后节点状态不同，就继续下面的事情，我们来看下面接下来做了什么事。接下来是判断当前遍历到的状态节点是否已经是树的叶子节点，如果是叶子节点就向树根部遍历，依次弹出上一级父节点直到遍历到整棵树的根节点。弹出是靠glstate这个参数来操作实现的注意一下。遍历到根节点并弹出状态后就直接返回了。

if (curStateBin === undefined) {
        //curStateBin已经到顶，弹出preStateBin的所有状态
        do {
            if (preStateBin._stateset !== undefined) {
                glstate.popStateSet();
            }
            preStateBin = preStateBin._parent;
        } while (preStateBin);
        return;
    }

我们再看看接下来还做了什么操作，这个看注释就能理解他的操作。

if (preStateBin === undefined) {
        //preStateBin已经到顶，压入curStateBin的所有状态
        //从子节点往根节点遍历获取所有的状态，但是推给glstate必须从根节点往子节点遍历
        //所以这里先塞到一个stack里面，然后再遍历stack推给glstate
        let stack = [];
        do {
            if (curStateBin._stateset !== undefined) {
                stack.push(curStateBin._stateset);
            }
            curStateBin = curStateBin._parent;
        } while (curStateBin);

        let size = stack.length - 1;
        for (let i = size; i >= 0; --i) {
            glstate.pushStateSet(stack[i]);
        }
        return;
    } else if (preStateBin._parent === curStateBin._parent) {
        // first handle the typical case which is two glstate groups
        // are neighbours.

        // glstate has changed so need to pop old glstate.
        if (preStateBin._stateset !== undefined) {
            glstate.popStateSet();
        }
        // and push new glstate.
        if (curStateBin._stateset !== undefined) {
            glstate.pushStateSet(curStateBin._stateset);
        }
        return;
    }

随后我们看看最后的操作。这波操作就是为了比较currStateBin和preStateBin这两个树节点的深度和对其向树根部的操作。

//先弹出状态，保证preStateBin和curStateBin达到树节点平级
    //无法确定两个树节点谁的深度值更多，两个都做一次循环
    while (preStateBin._depth > curStateBin._depth) {
        if (preStateBin._stateset !== undefined) {
            glstate.popStateSet();
        }
        preStateBin = preStateBin._parent;
    }

    // use return path to trace back steps to curStateBin.
    let stack = [];
    // need to pop back up to the same depth as the curr glstate group.
    while (curStateBin._depth > preStateBin._depth) {
        if (curStateBin._stateset !== undefined) {
            stack.push(curStateBin._stateset);
        }
        curStateBin = curStateBin._parent;
    }

    // now pop back up both parent paths until they agree.
    // should be this to conform with above case where two StateBin
    // nodes have the same parent
    //继续遍历直到两个树节点相同
    while (preStateBin !== curStateBin) {
        if (preStateBin._stateset !== undefined) {//pre的从GLState中出栈
            glstate.popStateSet();
        }
        preStateBin = preStateBin._parent;

        if (curStateBin._stateset !== undefined) {//当前的入栈，临时保存
            stack.push(curStateBin._stateset);
        }
        curStateBin = curStateBin._parent;
    }

    //遍历结束后，从临时栈中推入GLState里
    for (let i = stack.length - 1, l = 0; i >= l; --i) {
        glstate.pushStateSet(stack[i]);
    }

　　StateBin渲染状态树是对osg的StateSet单个模型渲染状态的管理数据结构，几乎在整个DrawActor的过程中都要大量应用，他的重要性不言而喻，鲫鱼也是一知半解的在学习这个数据结构，希望大家多提出宝贵的见解，多多斧正，谢谢同学们的支持关注。今天就到这里，下周再见。本文系原创，引用请注明出处：https://www.cnblogs.com/ccentry/p/10224312.html