opengl定义三维图形，实现三维三视图实验代码

下面是一个使用 OpenGL 实现三维三视图的代码示例，包含了正交投影和透视投影两种方式：

#include <GL/glut.h>

// 窗口大小
const int WINDOW_WIDTH = 600;
const int WINDOW_HEIGHT = 600;

// 三维坐标系范围
const double X_MIN = -10.0;
const double X_MAX = 10.0;
const double Y_MIN = -10.0;
const double Y_MAX = 10.0;
const double Z_MIN = -10.0;
const double Z_MAX = 10.0;

// 三个视图窗口的位置和大小
const int VIEWPORT1_X = 20;
const int VIEWPORT1_Y = 20;
const int VIEWPORT1_WIDTH = 200;
const int VIEWPORT1_HEIGHT = 200;

const int VIEWPORT2_X = 240;
const int VIEWPORT2_Y = 20;
const int VIEWPORT2_WIDTH = 200;
const int VIEWPORT2_HEIGHT = 200;

const int VIEWPORT3_X = 460;
const int VIEWPORT3_Y = 20;
const int VIEWPORT3_WIDTH = 200;
const int VIEWPORT3_HEIGHT = 200;

// 三维模型的顶点坐标
GLfloat vertices[][3] = {
    {-1.0, -1.0, -1.0},
    {1.0, -1.0, -1.0},
    {1.0, 1.0, -1.0},
    {-1.0, 1.0, -1.0},
    {-1.0, -1.0, 1.0},
    {1.0, -1.0, 1.0},
    {1.0, 1.0, 1.0},
    {-1.0, 1.0, 1.0}
};

// 三维模型的面
GLint faces[][4] = {
    {0, 1, 2, 3},
    {1, 5, 6, 2},
    {5, 4, 7, 6},
    {4, 0, 3, 7},
    {0, 4, 5, 1},
    {3, 2, 6, 7}
};

// 初始化 OpenGL
void init(void) {
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0, 1.0, 1.0, 20.0);
    glMatrixMode(GL_MODELVIEW);
}

// 绘制三维模型
void drawModel(void) {
    int i;

    glBegin(GL_QUADS);
    for (i = 0; i < 6; i++) {
        glNormal3fv(&vertices[faces[i][0]][0]);
        glVertex3fv(&vertices[faces[i][0]][0]);
        glNormal3fv(&vertices[faces[i][1]][0]);
        glVertex3fv(&vertices[faces[i][1]][0]);
        glNormal3fv(&vertices[faces[i][2]][0]);
        glVertex3fv(&vertices[faces[i][2]][0]);
        glNormal3fv(&vertices[faces[i][3]][0]);
        glVertex3fv(&vertices[faces[i][3]][0]);
    }
    glEnd();
}

// 绘制三个视图窗口
void drawViewport1(void) {
    glViewport(VIEWPORT1_X, VIEWPORT1_Y, VIEWPORT1_WIDTH, VIEWPORT1_HEIGHT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(X_MIN, X_MAX, Y_MIN, Y_MAX, Z_MIN, Z_MAX);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    drawModel();
}

void drawViewport2(void) {
    glViewport(VIEWPORT2_X, VIEWPORT2_Y, VIEWPORT2_WIDTH, VIEWPORT2_HEIGHT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(X_MIN, X_MAX, Y_MIN, Y_MAX, Z_MIN, Z_MAX);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(5.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
    drawModel();
}

void drawViewport3(void) {
    glViewport(VIEWPORT3_X, VIEWPORT3_Y, VIEWPORT3_WIDTH, VIEWPORT3_HEIGHT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(X_MIN, X_MAX, Y_MIN, Y_MAX, Z_MIN, Z_MAX);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, -1.0);
    drawModel();
}

// 绘制场景
void display(void) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    drawViewport1();
    drawViewport2();
    drawViewport3();
    glutSwapBuffers();
}

// 窗口大小改变时的回调函数
void reshape(int width, int height) {
    glViewport(0, 0, width, height);
}

int main(int argc, char **argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(WINDOW_WIDTH, WINDOW_HEIGHT);
    glutCreateWindow("3D Viewport Demo");
    init();
    glEnable(GL_DEPTH_TEST);
    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutMainLoop();
    return 0;
}

运行该程序后，会弹出一个窗口，其中包含了三个视图窗口，分别显示了三个视图的效果。可以通过修改 `gluPerspective` 或 `glOrtho` 函数的参数来调整投影方式和视角大小，从而得到不同的效果。