c++ - 使用 txt 文件中的数据根据​​时间围绕其顶点旋转圆锥体

Question

我有一个 txt 文件，其中的数据是顶部旋转(3D 中)质心位置的时间函数。所以我想用一个圆锥体来表示这个顶部，我拥有的数据应该代表圆锥体基础的中心，及时围绕顶点旋转。

我有一个代表圆锥体的代码，我设法弄清楚了如何围绕底部旋转它。但是我没有设法围绕它的 Vertex 旋转它。我也不知道如何用我的数据移动圆锥体。

#include <GL\glut.h>

GLfloat xRotated, yRotated, zRotated;
// Cone
GLdouble base=1;
GLdouble height=1.5;
GLint slices =50;
GLint stacks =50;


void displayCone(void)
{
    glMatrixMode(GL_MODELVIEW);
    // clear the drawing buffer.
    glClear(GL_COLOR_BUFFER_BIT);
    // clear the identity matrix.
    glLoadIdentity();
    // traslate the draw by z = -4.0
    // Note this when you decrease z like -8.0 the drawing will looks       far , or smaller.
    glTranslatef(0.0,0.0,-4.5);
    // Red color used to draw.
    glColor3f(0.8, 0.2, 0.1); 
    // changing in transformation matrix.
    // rotation about X axis
    glRotatef(xRotated,1.0,0.0,0.0);
    // rotation about Y axis
    glRotatef(yRotated,0.0,1.0,0.0);
    // rotation about Z axis
    glRotatef(zRotated,0.0,0.0,1.0);
    // scaling transfomation 
    glScalef(1.0,1.0,1.0);
    // built-in (glut library) function , draw you a Cone.

    glutSolidCone(base,height,slices,stacks);
    // Flush buffers to screen

    glFlush();        
    // sawp buffers called because we are using double buffering 
    // glutSwapBuffers();
}


void idleCone(void)
{
    xRotated += 0.1;
    yRotated += 0.1;
    zRotated += 0.1; 

    displayCone();
}


int main (int argc, char **argv)
{
    //Initialize GLUT
    glutInit(&argc, argv);
    //double buffering used to avoid flickering problem in animation
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);  
    // window size
    glutInitWindowSize(400,350);
    // create the window 
    glutCreateWindow("Cone Rotating Animation");
    glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
    xRotated = yRotated = zRotated = 30.0;
    xRotated=33;
    yRotated=40;
    glClearColor(0.0,0.0,0.0,0.0);
    //Assign  the function used in events
    glutDisplayFunc(displayCone);
    glutReshapeFunc(reshapeCone);
    glutIdleFunc(idleCone);
    //Let start glut loop
    glutMainLoop();
    return 0;
}  

我已经设法用 Gnuplot 表示质心在 3D 中移动，但是用一个用 OpenGL 旋转的圆锥体来表现会更漂亮

Answer 1

如果你想围绕它的顶部旋转圆锥体，那么你必须以这种方式平移圆锥体，圆锥体的顶部在原点:

glTranslatef(0.0, 0.0, -height);

这必须在应用旋转和缩放之前完成。自 glTranslate (和其他矩阵变换)将当前矩阵乘以一个新的变换矩阵，glTranslate 指令必须在其他模型变换(如 glRotate 和 glScale:

void displayCone(void)
{
    glMatrixMode(GL_MODELVIEW);
    // clear the drawing buffer.
    glClear(GL_COLOR_BUFFER_BIT);
    // clear the identity matrix.
    glLoadIdentity();
    // traslate the draw by z = -4.0
    // Note this when you decrease z like -8.0 the drawing will looks       far , or smaller.
    glTranslatef(0.0,0.0,-4.5);
    // Red color used to draw.
    glColor3f(0.8, 0.2, 0.1); 
    // changing in transformation matrix.
    // rotation about X axis
    glRotatef(xRotated,1.0,0.0,0.0);
    // rotation about Y axis
    glRotatef(yRotated,0.0,1.0,0.0);
    // rotation about Z axis
    glRotatef(zRotated,0.0,0.0,1.0);

    // scaling transfomation 
    glScalef(1.0,1.0,1.0);
    // built-in (glut library) function , draw you a Cone.

    // move the peak of the cone to the origin
    glTranslatef(0.0, 0.0, -height);

    glutSolidCone(base,height,slices,stacks);
    // Flush buffers to screen

    glFlush();        
    // sawp buffers called because we are using double buffering 
    // glutSwapBuffers();
}

---

根据评论扩展:

Could you add a short code snipped to help me understanding what I should do to rotate the cone with the datas stored in the array ?

查看如何逐行读取文件 Read file line by line using ifstream in C++ .在以下示例中，将数据存储到 std::vector ，其中每个元素包含的 std::array共 3 个 GLfloat:

#include <vector>
#include <array>
#include <fstream>
#include <string>
#include <sstream>

void ReadData( const char *fileName, std::vector<std::array<GLfloat, 3>> &data )
{
    std::ifstream dataFile(fileName);
    std::string line;
    while (std::getline(dataFile, line))
    {
        std::istringstream insstr(line);
        GLfloat x, y, z;
        if (!(insstr >> x >> y >> z))
            break; // reading error

        data.push_back( { x, y, z } );
    }
}

读取数据并通过索引访问 3 个角度(例如 j):

std::vector<std::array<GLfloat, 3>> data;

ReadData( "mydata.txt", data );

xRotated = data[j][0];
yRotated = data[j][1];
zRotated = data[j][2];