opengl 绘制地球

要使用OpenGL绘制地球，可以按照以下步骤进行：

1.创建一个OpenGL窗口和环境。

2.加载地球的纹理图像，并将其映射到一个球体上。

3.创建一个球体的顶点缓冲区，并将其绑定到OpenGL上下文中。

4.编写着色器程序来绘制球体，并将其绑定到OpenGL上下文中。

5.使用OpenGL命令来绘制球体，并将其显示在OpenGL窗口中。

以下是一个简单的OpenGL绘制球体的代码示例：

#include <GL/glut.h>

#include <iostream>

#include <cmath>

using namespace std;

#define PI 3.14159265358979323846

// 地球半径

const double EARTH_RADIUS = 6378.137;

// 角度转弧度

double Angle2Radian(double angle) {

  return angle * PI / 180.0;

}

// 绘制球体

void DrawSphere(double r) {

  const int n = 50;

  const int m = 50;

  double angle1, angle2;

  double x1, y1, z1, x2, y2, z2;

  double step1 = PI / n;

  double step2 = 2 * PI / m;

  for (int i = 0; i < n; i++) {

    angle1 = i * step1;

    angle2 = angle1 + step1;

    glBegin(GL_TRIANGLE_STRIP);

    for (int j = 0; j <= m; j++) {

      x1 = r * sin(angle1) * cos(j * step2);

      y1 = r * sin(angle1) * sin(j * step2);

      z1 = r * cos(angle1);

      x2 = r * sin(angle2) * cos(j * step2);

      y2 = r * sin(angle2) * sin(j * step2);

      z2 = r * cos(angle2);

      // 绘制三角形

      glVertex3d(x1, y1, z1);

      glVertex3d(x2, y2, z2);

    }

    glEnd();

  }

}

// 显示回调函数

void Display() {

  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  // 绘制球体

  DrawSphere(EARTH_RADIUS);

  glFlush();

}

// 窗口大小变化回调函数

void Reshape(int w, int h) {

  glViewport(0, 0, w, h);

  glMatrixMode(GL_PROJECTION);

  glLoadIdentity();

  gluPerspective(45.0, (double)w / (double)h, 1.0, 1000.0);

  glMatrixMode(GL_MODELVIEW);

  glLoadIdentity();

  gluLookAt(0, 0, 1000, 0, 0, 0, 0, 1, 0);

}

// 初始化函数

void Init() {

  glEnable(GL_DEPTH_TEST);

  glEnable(GL_TEXTURE_2D);

  // 加载地球纹理图像

  GLuint tex = 0;

  glGenTextures(1, &tex);

  glBindTexture(GL_TEXTURE_2D, tex);

  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);

  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

  glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 1024, 512, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);

  // 设置材质属性

  GLfloat mat_ambient[] = {0.0, 0.0, 0.0, 1.0};

  GLfloat mat_diffuse[] = {1.0, 1.0, 1.0, 1.0};

  GLfloat mat_specular[] = {1.0, 1.0, 1.0, 1.0};

  GLfloat mat_shininess[] = {100.0};

  glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);

  glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);

  glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);

  glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);

  glEnable(GL_LIGHTING);

  glEnable(GL_LIGHT0);

  // 设置光源属性

  GLfloat light_position[] = {0.0, 0.0, 500.0, 1.0};

  GLfloat light_ambient[] = {0.0, 0.0, 0.0, 1.0};

  GLfloat light_diffuse[] = {1.0, 1.0, 1.0, 1.0};

  GLfloat light_specular[] = {1.0, 1.0, 1.0, 1.0};

  glLightfv(GL_LIGHT0, GL_POSITION, light_position);

  glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);

  glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);

  glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);

}

// 主函数

int main(int argc, char *argv[]) {

  glutInit(&argc, argv);

  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);

  glutInitWindowSize(800, 600);

  glutCreateWindow("OpenGL Sphere");

  glutDisplayFunc(Display);

  glutReshapeFunc(Reshape);

  Init();

  glutMainLoop();

  return 0;

}