OpenGL--二次几何体

• 理论基础
  二次几何体：就是指一些常用的三维物体，如球体，圆柱体，圆盘和圆锥体等，OpenGL核心库也不能直接模拟和渲染，但我们可以使用GLU库来创建这些二次几何体。

  创建和渲染二次几何体的过程：1，创建一个二次对象 2，注册一个错误回调 3，指定二次对象的渲染属性(绘制模式，法线类型，是否生成纹理坐标，法线方向) 4，调用二次几何体渲染函数 5，删除二次对象。

注释：二次几何体opengl 3.1以后基本已经废弃了。

• 代码示例

#include "GLTools.h"

#ifdef __APPLE__
#include <glut/glut.h>
#else
#define FREEGLUT_STATIC
#include <GL/glut.h>
#endif

#ifndef CALLBACK
#define CALLBACK
#endif

GLuint startList;

//注册错误回调
void CALLBACK errorCallback(GLenum errorCode)
{
    const GLubyte *estring;

    estring = gluErrorString(errorCode);
    fprintf(stderr, "Quadric Error: %s\n", estring);
    exit(0);
}

void init(void)
{
    GLUquadricObj *qobj;
    GLfloat mat_ambient[] = { 0.5, 0.5, 0.5, 1.0 };
    GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
    GLfloat mat_shininess[] = { 50.0 };
    GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };
    GLfloat model_ambient[] = { 0.5, 0.5, 0.5, 1.0 };

    glClearColor(0.0, 0.0, 0.0, 0.0);

    glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);
    glLightfv(GL_LIGHT0, GL_POSITION, light_position);
    glLightModelfv(GL_LIGHT_MODEL_AMBIENT, model_ambient);

    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);

    startList = glGenLists(4);
    //创建二次对象
    qobj = gluNewQuadric();
    //注册错误处理回调
    gluQuadricCallback(qobj, GLU_ERROR,
                       (void(__stdcall*)())errorCallback);
    //指定二次对象的渲染属性
    gluQuadricDrawStyle(qobj, GLU_FILL); //绘制模式:填充
    gluQuadricNormals(qobj, GLU_SMOOTH);//为每个顶点生成一条法线且采用光滑着色模式
    glNewList(startList, GL_COMPILE);
    //4种二次图元渲染
    gluSphere(qobj, 0.75, 15, 10);//球体
    glEndList();

    gluQuadricDrawStyle(qobj, GLU_FILL);//填充绘制
    gluQuadricNormals(qobj, GLU_FLAT);//单色着色模式
    glNewList(startList+1, GL_COMPILE);
    gluCylinder(qobj, 0.5, 0.3, 1.0, 15, 5);//台锥体
    glEndList();

    gluQuadricDrawStyle(qobj, GLU_LINE);//线框绘制
    gluQuadricNormals(qobj, GLU_NONE);//不生成法线(没有光照)
    glNewList(startList+2, GL_COMPILE);
    gluDisk(qobj, 0.25, 1.0, 20, 4);//圆盘
    glEndList();

    gluQuadricDrawStyle(qobj, GLU_SILHOUETTE);//线框模式且同一平面的两个面不绘制它们之间的边
    gluQuadricNormals(qobj, GLU_NONE);
    glNewList(startList+3, GL_COMPILE);
    gluPartialDisk(qobj, 0.0, 1.0, 20, 4, 0.0, 225.0);//部分圆盘
    glEndList();

    gluDeleteQuadric(qobj);//删除二次对象，释放空间
}

void display(void)
{
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glPushMatrix();

    glEnable(GL_LIGHTING);
    glShadeModel (GL_SMOOTH);
    glTranslatef(-1.0, -1.0, 0.0);
    glCallList(startList);

    glShadeModel (GL_FLAT);
    glTranslatef(0.0, 2.0, 0.0);
    glPushMatrix();
    glRotatef(300.0, 1.0, 0.0, 0.0);
    glCallList(startList+1);
    glPopMatrix();

    glDisable(GL_LIGHTING);
    glColor3f(0.0, 1.0, 1.0);
    glTranslatef(2.0, -2.0, 0.0);
    glCallList(startList+2);

    glColor3f(1.0, 1.0, 0.0);
    glTranslatef(0.0, 2.0, 0.0);
    glCallList(startList+3);

    glPopMatrix();
    glFlush();
}

void reshape (int w, int h)
{
    glViewport(0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= h)
        glOrtho(-2.5, 2.5, -2.5*(GLfloat)h/(GLfloat)w,
                2.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0);
    else
        glOrtho(-2.5*(GLfloat)w/(GLfloat)h,
                2.5*(GLfloat)w/(GLfloat)h, -2.5, 2.5, -10.0, 10.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void keyboard(unsigned char key, int x, int y)
{
    switch (key) {
        case 27:
            exit(0);
            break;
    }
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(100, 100);
    glutCreateWindow(argv[0]);
    init();
    glutDisplayFunc(display); 
    glutReshapeFunc(reshape);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
    return 0;
}