#include "stdlib.h"  
#include <OpenGL/glext.h>  
#include <GLUT/GLUT.h>  
  
#define BUFFER_OFFSET(bytes) ((GLubyte*) NULL + (bytes))  
#define VERTICES 0  
#define INDICES 1  
#define NUM_BUFFERS 6  
GLuint buffers[NUM_BUFFERS];  
  
GLfloat vertices[][3] = {  
    {-1.0f,-1.0f,-1.0f},  
    {1.0f,-1.0f,-1.0f},  
    {1.0f,1.0f,-1.0f},  
    {-1.0f,1.0f,-1.0f},  
    {-1.0f,-1.0f,1.0f},  
    {1.0f,-1.0f,1.0f},  
    {1.0f,1.0f,1.0f},  
    {-1.0f,1.0f,1.0f}  
};  
GLubyte indices[][4] = {  
    {0,1,2,3},  
    {4,7,6,5},  
    {0,4,5,1},  
    {3,2,6,7},  
    {0,3,7,4},  
    {1,5,6,2}  
};  
  
GLfloat* bdata;  
  
void changeSize(int w, int h)  
{  
    glViewport(0,0,(GLsizei)w,(GLsizei)h);  
    glMatrixMode(GL_PROJECTION);  
    glLoadIdentity();  
    gluPerspective(45.0,(double)w/(double)h,0.01,30);  
    glMatrixMode(GL_MODELVIEW);  
    glLoadIdentity();  
}  
  
void keyDown(unsigned char key, int x, int y)  
{  
    switch (key)  
    {  
        case'b':  
            bdata = (GLfloat*)glMapBuffer(GL_ARRAY_BUFFER,GL_READ_WRITE);  
            for (int i =0; i <24; i ++)  
            {  
                *(bdata + i) *=1.1f;  
            }  
            glUnmapBuffer(GL_ARRAY_BUFFER);  
            glutPostRedisplay();  
            break;  
    }  
}  
  
void mouse(int button, int state, int x, int y)  
{  
      
}  
void display(void)  
{  
    glLoadIdentity();  
    glTranslatef(0.0f,0.0f,-5.0f);  
    glRotatef(30.0f,1.0f,1.0f,0.0f);  
  
   // 6. 绘制， 这个地方注意的是最后一个参数，这个与普通的非VBO最大的不同就在这里  
    glDrawElements(GL_QUADS,24,GL_UNSIGNED_BYTE,BUFFER_OFFSET(0));  
    //glDrawArrays(GL_TRIANGLE_FAN, 0, 8);  
    glutSwapBuffers();  
}  
  
void init(void)  
{  
    glClearColor(0.0f,0.0f,0.0f,0.0f);  
    glShadeModel(GL_FLAT);  
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  
  
    //1.  创建缓冲区对象，系统会自动创建缓动区标示符放入到buffers中，可以使用glIsBuffer()函数，判断一个标示符是否被使用  
    glGenBuffers(NUM_BUFFERS ,buffers);  
    //2.  激活缓冲区对象，绑定缓冲区对象表示未来选择的操作将影响哪个缓冲区。 如果要金融缓冲区对象，可以用0来作为缓冲区对象的标示符， 第一个参数target可以为GL_ARRAY_BUFFER,GL_ELEMENT_ARRAY_FUFFER  
    glBindBuffer(GL_ARRAY_BUFFER,buffers[VERTICES]);  
    //3. 用数据分配和初始化缓冲区对象  
    glBufferData(GL_ARRAY_BUFFER,sizeof(vertices),vertices,GL_DYNAMIC_DRAW);  
    //4. 指定相对于缓冲区起始位置的偏移量  
    glVertexPointer(3,GL_FLOAT,0,BUFFER_OFFSET(0));  
    //5.一定不要忘记启动  
    glEnableClientState(GL_VERTEX_ARRAY);  
      
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,buffers[INDICES]);  
    glBufferData(GL_ELEMENT_ARRAY_BUFFER,sizeof(indices),indices,GL_STATIC_DRAW);  
}  
  
int main(int argc, char* argv[])  
{  
    glutInit(&argc, argv);  
    glutInitDisplayMode(GL_DOUBLE | GLUT_RGBA | GLUT_DEPTH);  
    glutInitWindowSize(512, 512);  
    glutCreateWindow("Buffer Demo");  
     init();  
    glutReshapeFunc(changeSize);  
    glutMouseFunc(mouse);  
    glutKeyboardFunc(keyDown);  
    glutDisplayFunc(display);  
     
    glutMainLoop();  
    return 0;  
}