c++ - 在opengl中创建一个分形树

Question

在 opengl 中创建分形时遇到一点问题。这是我当前的代码

void generateTree(){
  Point3f startPoint({0.0f,0.0f,0.0f});
  Point3f endPoint({1.0f,0.0f,0.0f});
  float rotation = 90.0f;
  glutWireSphere(0.05, 4, 4);
  _generateTreeBranches(startPoint,1.0f,rotation,0);
}

void _generateTreeBranches(const Point3f& newPosition,
                       float length,
                       float rotation,
                       const int depth)
{
  if(depth > MAX_DEPTH) return;
  cout << "at depth = " << depth << endl;


  if(depth == 0){
      glColor3f(1.0f,1.0f,1.0f);
  }else if(depth == 1){
      glColor3f(1.0f,0.0f,0.0f);
  }else{
      glColor3f(0.0f,1.0f,0.0f);
  }

  glTranslatef(newPosition.x,newPosition.y,newPosition.z);
  glRotatef(rotation, 0.0f, 0.0f, 1.0f);
  drawLine(length);
  glRotatef(-rotation, 0.0f, 0.0f, 1.0f);
  glTranslatef(-newPosition.x,-newPosition.y,-newPosition.z);



  const float newLength = length * BRANCH_LENGTH_DECREASE_FACTOR;
  int nextDepth = depth + 1;
  Point3f nextPosition = {newPosition.x+length, newPosition.y, newPosition.z};

  float leftRotation = rotation + CHILD_BRANCH_ANGLE * nextDepth;
  _generateTreeBranches(nextPosition,newLength,leftRotation,nextDepth);

  float rightRotation = rotation - CHILD_BRANCH_ANGLE * nextDepth;
  _generateTreeBranches(nextPosition,newLength,rightRotation,nextDepth);

}

虽然旋转似乎是正确的，但定位不正确。新分支不是从父分支的终点开始绘制的。有人可以帮我解决这个问题。查看完整代码 here

Answer 1

nextPosition 的公式不正确，因为它没有考虑当前分支所面对的方向

 Point3f nextPosition = {newPosition.x+length, newPosition.y, newPosition.z};

应该是这样的(请仔细检查):

Point3f nextPosition = {newPosition.x+length*cos(rotation), newPosition.y+length*sin(rotation), newPosition.z};

另外，请像这样立即使用 glLoadIdentity() 重置矩阵:

glTranslatef(newPosition.x,newPosition.y,newPosition.z);
glRotatef(rotation, 0.0f, 0.0f, 1.0f);
drawLine(length);
glLoadIdentity();

它会比你试图做的更清楚。