递归画树（Qt实现）1. 问题描述2. 解决思路3. 代码实现4. 运行结果5. 小结

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我是靠谱客的博主喜悦小甜瓜，最近开发中收集的这篇文章主要介绍递归画树（Qt实现）1. 问题描述2. 解决思路3. 代码实现4. 运行结果5. 小结，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

1. 问题描述

用递归算法绘制一棵树

2. 解决思路

用二叉树的数据结构来描述树的结构，首先创建一个二叉树，创建时要初始化节点的一些信息，伪代码如下：

If  current depth is last
    then return null
End If
Create a branch
If current branch is left
    then initial the branch as a left branch
Else
    then initial the branch as a right branch
End If
Create the left branch of this recursively
Create the right branch of this recursively
return the root branch

然后再遍历二叉树，遍历的同时绘制树枝，伪代码如下：

If  current branch has left branch
    then paint the left branch
End If
If current branch has right branch
    then paint the left branch
End If
Paint the left branch of this recursively
Paint the right branch of this recursively

3. 代码实现

创建树的代码：

Branch *DrawTrees::createTree(Branch *preRoot, bool isLeft)
{
    if(preRoot->depth > depth)//判断是否到达设置的深度
        return NULL;
 
    Branch *root = new Branch();
    if(!root)
        return NULL;
 
    root->depth = preRoot->depth + 1;
    if(root->depth < 3)
    {//最底下三层的树枝角度较小
        if(isLeft)
        {
           root->angle = preRoot->angle + qrand()%15;
           root->length = preRoot->length - preRoot->length / (3+qrand()%7);
        }
        else
        {
           root->angle = preRoot->angle - qrand()%15;
           root->length = preRoot->length - preRoot->length / (3+qrand()%7);
        }
        root->width = preRoot->width * 0.8;
    }
    else
    {
        if(branchNumCount[root->depth] >= maxBranchNum[root->depth])
            return NULL;
        else
        {
            if(isLeft)
                root->angle = preRoot->angle+(45-root->depth*3+qrand()%(40-root->depth*2));
            else
                root->angle = preRoot->angle-(45-root->depth*3+qrand()%(40-root->depth*2));
 
            root->length = preRoot->length-preRoot->length/(3+qrand()%7);
            root->width = preRoot->width * 0.618;
            branchNumCount[root->depth]++;
        }
 
    }
     //计算当前树枝起点的坐标
    root->x= preRoot->x + root->length*cos(root->angle*ONEANGLE);
    root->y= preRoot->y - root->length*sin(root->angle*ONEANGLE);
     //当树枝宽带减小到1时不再减小
    if(root->width < 1)
        root->width = 1;
 
    root->left = createTree(root, true);  //递归创建左子树
    root->right = createTree(root, false); //递归创建右子树
 
    return root ;
 
}

绘制树的代码：

void DrawTrees::paintTree(Branch *root)
{
    if(!root)
        return;

    int dstX,dstY;

    if(!root->left) 
    {//左子树为空则画叶子
        dstX=root->x+1;
        dstY=root->y+1;

        painter->setPen(QPen(QBrush(QColor(0,140,0,255)),
                             LEAVE_WIDTH,
                             Qt::SolidLine,
                             Qt::RoundCap));

        painter->drawLine(root->x,root->y,dstX,dstY);

    }
    else
    {//否则画树枝
        dstX=root->left->x;
        dstY=root->left->y;

        painter->setPen(QPen(QColor(160, 82, 45),
                             root->width,
                             Qt::SolidLine,
                             Qt::RoundCap));
        painter->drawLine(root->x,root->y,dstX,dstY);
    }

    if(!root->right)
    {
        dstX=root->x+1;
        dstY=root->y+1;

        painter->setPen(QPen(QBrush(QColor(0,140,0,255)),
                                    LEAVE_WIDTH,
                                    Qt::SolidLine,
                                    Qt::RoundCap));
        painter->drawLine(root->x,root->y,dstX,dstY);
    }
    else
    {
        dstX=root->right->x;
        dstY=root->right->y;

        painter->setPen(QPen(QColor(160, 82, 45),
                             root->width,
                             Qt::SolidLine,
                             Qt::RoundCap));
        painter->drawLine(root->x,root->y,dstX,dstY);
    }

    paintTree(root->left);//递归绘制左子树
    paintTree(root->right);//递归绘制右子树

}