分形之树（Tree）

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[] = vEnd;

    //pVertices[1] = pVertices[0] + vSub*trunk_c;

    pVertices[].x = pVertices[].x + trunk*cosf(alfa + trunk_angle);

    pVertices[].y = pVertices[].y + trunk*sinf(alfa + trunk_angle);

    pVertices[].z = 0.0f;

    pVertices[] = vEnd;

    pVertices[].x = pVertices[].x + branch*cosf(alfa + branch_angle);

    pVertices[].y = pVertices[].y + branch*sinf(alfa + branch_angle);

    pVertices[].z = 0.0f;

    pVertices[] = pVertices[];

    pVertices[].x = pVertices[].x + branch*cosf(alfa - branch_angle);

    pVertices[].y = pVertices[].y + branch*sinf(alfa - branch_angle);

    pVertices[].z = 0.0f;

    pVertices[] = vStart + vSub*0.55f;

    pVertices[].x = pVertices[].x + branch2*cosf(alfa + branch_angle);

    pVertices[].y = pVertices[].y + branch2*sinf(alfa + branch_angle);

    pVertices[].z = 0.0f;

    pVertices[] = pVertices[];

    pVertices[].x = pVertices[].x + branch2*cosf(alfa - branch_angle);

    pVertices[].y = pVertices[].y + branch2*sinf(alfa - branch_angle);

    pVertices[].z = 0.0f;

}