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

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

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));elseroot->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 ;}

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}