如何使用带有OpenGL的Nurbs知道一个特定的值位置?

I am using OpenGL to create a nurbs surface (gluNurbSurface(...)) and I would like to know how reach the normal value to the control points(black dot) to the surface market as a red dot. With this information I will be able to calculate the distance between them.

我正在使用OpenGL创建一个nurbs曲面(gluNurbSurface(…))，我想知道如何将控制点(黑点)作为一个红点到达曲面市场。有了这些信息，我就能计算出它们之间的距离。

Added In order to get another answers or improve the subjected I would like to write part of the code, I hope can get more help:

为了得到另一个答案或改进我想写的部分代码的被试，我希望能得到更多的帮助:

In this part you can observe how I initialize the nurbs.

在这一部分中，您可以观察我如何初始化nurbs。

init_surface();

   theNurb = gluNewNurbsRenderer();
   gluNurbsProperty(theNurb, GLU_SAMPLING_TOLERANCE, 50.0);
   gluNurbsProperty(theNurb, GLU_DISPLAY_MODE, GLU_FILL);
   gluNurbsCallback(theNurb, GLU_ERROR, 
                    (GLvoid (*)()) nurbsError);

Next the surface is created with their parameters.

接下来，使用它们的参数创建表面。

gluBeginSurface(theNurb);
    gluNurbsSurface(theNurb,
            U+ordenU, knotsU,
            V+ordenV, knotsV,
            V * 3,
            3,
            &ctlpoints[0][0][0],
            ordenU, ordenV,
            GL_MAP2_VERTEX_3);

   gluEndSurface(theNurb);

Remember I am using C. And in this moment I am trying to introduce the values of the nurbs into a vector with the function proposed by genpfault in the first answer but I do not know in which part I have to add them.

记住，我用的是c，在这一刻，我试图把nurbs的值引入到一个向量中，第一个答案是由genpfault提出的函数，但是我不知道我要在哪一部分添加它们。

1 个解决方案

#1

Set a GLU_NURBS_NORMAL_DATA callback via gluNurbsCallback(). A GLU_NURBS_VERTEX_DATA callback would also be useful.

通过gluNurbsCallback()设置GLU_NURBS_NORMAL_DATA回调。GLU_NURBS_VERTEX_DATA回调也很有用。

Point *userData (via gluNurbsCallbackData()) at some sort of dynamic array data-structure to hold the points/normals. If you were using C++ I'd recommend a std::vector of Eigen::Vector3fs.

点*userData(通过gluNurbsCallbackData())在某种动态数组数据结构上保存点/法线。如果您正在使用c++，我建议您使用std::: Eigen::Vector3fs的向量。

#1