似乎每一个有关分形的教程都要讲到分形树，大概是因为树是生活中最常见的分形实物吧。这一节将展示下如何一步一步地生长出一棵树来。其实现算法不难，就是在每一次生长迭代中，使线段生长出几条新的线段来。

核心代码:

static void FractalTree(const Vector3& vStart, const Vector3& vEnd,                         Yreal trunk_angle, Yreal branch_angle, Yreal trunk_c, Yreal branch_c,                         Vector3* pVertices){    Vector3 vSub = vEnd - vStart;    Yreal len = D3DXVec3Length(&vSub);    Yreal alfa = atan2f(vSub.y, vSub.x);    Yreal trunk = len*trunk_c;    Yreal branch = len*branch_c;    Yreal branch2 = branch*1.25f;    pVertices[0] = vEnd;    //pVertices[1] = pVertices[0] + vSub*trunk_c;    pVertices[1].x = pVertices[0].x + trunk*cosf(alfa + trunk_angle);    pVertices[1].y = pVertices[0].y + trunk*sinf(alfa + trunk_angle);    pVertices[1].z = 0.0f;    pVertices[2] = vEnd;    pVertices[3].x = pVertices[2].x + branch*cosf(alfa + branch_angle);    pVertices[3].y = pVertices[2].y + branch*sinf(alfa + branch_angle);    pVertices[3].z = 0.0f;    pVertices[4] = pVertices[2];    pVertices[5].x = pVertices[4].x + branch*cosf(alfa - branch_angle);    pVertices[5].y = pVertices[4].y + branch*sinf(alfa - branch_angle);    pVertices[5].z = 0.0f;    pVertices[6] = vStart + vSub*0.55f;    pVertices[7].x = pVertices[6].x + branch2*cosf(alfa + branch_angle);    pVertices[7].y = pVertices[6].y + branch2*sinf(alfa + branch_angle);    pVertices[7].z = 0.0f;    pVertices[8] = pVertices[6];    pVertices[9].x = pVertices[8].x + branch2*cosf(alfa - branch_angle);    pVertices[9].y = pVertices[8].y + branch2*sinf(alfa - branch_angle);    pVertices[9].z = 0.0f;}

软件截图：

 

树的生成需要若干个参数：树干的偏角，树枝的偏角，树干的生长长度，树枝的生长长度，修改下参数可以得到如下形状的树：

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