#include "stdafx.h"
#include "stdlib.h"
#include "gl/glew.h"
#include "gl/glut.h"

#define BUFFER_OFFSET(bytes) ((GLubyte*) NULL + (bytes))
#define VERTICES 0
#define INDICES 1
#define NUM_BUFFERS 2
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);

glDrawElements(GL_QUADS,24,GL_UNSIGNED_BYTE,BUFFER_OFFSET(0));

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);
glewInit();
glGenBuffers(NUM_BUFFERS,buffers);
glBindBuffer(GL_ARRAY_BUFFER,buffers[VERTICES]);
glBufferData(GL_ARRAY_BUFFER,sizeof(vertices),vertices,GL_DYNAMIC_DRAW);
glVertexPointer(3,GL_FLOAT,0,BUFFER_OFFSET(0));

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");
glutReshapeFunc(changeSize);
glutMouseFunc(mouse);
glutKeyboardFunc(keyDown);
glutDisplayFunc(display);
init();
glutMainLoop();
return0;
}