OpenGL学习八：缓冲区对象

 

产生原因
OpenGL是按照CS结构设计的，当OPENGL需要数据的时候，必须从客户机内存传递到服务器，如果客户机和服务器属于不同的计算机，这样的数据效率缓慢，并且有时是冗余的

做法：
1.创建缓冲区对象
glGenBuffers(NUM_BUFFER,buffers);
2.激活缓冲区对象
glBindBuffer(target,buffer);
GL_ARRAY_BUFFER //坐标，颜色 等
GL_ELEMENT_ARRAY_BUFFER //索引坐标
GL_TEXTURE_BUFFER//纹理缓冲
……
3.用数据分配和初始化缓冲区对象
glBufferData(target,size,data,usage)

usage:
#define GL_STREAM_DRAW 0x88E0
#define GL_STREAM_READ 0x88E1
#define GL_STREAM_COPY 0x88E2
#define GL_STATIC_DRAW 0x88E4
#define GL_STATIC_READ 0x88E5
#define GL_STATIC_COPY 0x88E6
#define GL_DYNAMIC_DRAW 0x88E8
#define GL_DYNAMIC_READ 0x88E9
DRAW: 客户机指定了用于渲染的数据
READ:从OPENGL缓冲区读取数据值，并且在应用程序中用于各种鱼渲染不直接相关的计算过程
COPY:从OPENGL缓冲区读取数据值,作为用于渲染的数据

STREAM:缓冲区对象中数据需要经常更新，但是作为绘图或其他操作使用较少
STATIC：缓冲区数据只指定1次，但是这些数据使用频率非常高
DYNAMIC:缓冲区数据常常更新，并且使用频率也很高
4.激活顶点数组
5.为顶点数组指定数据，这里指定的数据在服务器存储的内存地址

glGenBuffers(NUM_BUFFER,buffers);
 glBindBuffer(GL_ARRAY_BUFFER,buffers[VERTICES]);
 glBufferData(GL_ARRAY_BUFFER,sizeof(vertices),vertices,GL_STATIC_DRAW);
 glVertexPointer(3,GL_FLOAT,0,0);
 glEnableClientState(GL_VERTEX_ARRAY);

 glBindBuffer(GL_ARRAY_BUFFER,buffers[COLOR]);
 glBufferData(GL_ARRAY_BUFFER,sizeof(colors),colors,GL_STATIC_DRAW);
 glColorPointer(3,GL_FLOAT,0,0);
 glEnableClientState(GL_COLOR_ARRAY);

 glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,buffers[INDICES]);
 glBufferData(GL_ELEMENT_ARRAY_BUFFER,sizeof(indices),indices,GL_STATIC_DRAW);

缓冲区数据更改

方法1：
glBufferSubData(Glenum target,GLintptr offset,Glsizeiptr size,const Glvoid* data)
用data指向数据更新target相关联的当前绑定缓冲区的对象中offset开始的size个字节数据

方法2：
使用glMapBuffer返回一个指向缓冲区对象的指针，可以在这个缓冲区写入新值。在完成了对缓冲区对象的数据更新之后，可以调用glUnmapBuffer(target)取消都这个缓冲区的映射。

数据在缓冲区对象向之间复制
void glCopyBufferSubData(GLenum readbuffer,GLenum writebuffer,GLinrptr readoffset,GLinrptr writeoffset,Glsizeiptr size)

Glvoid* glMapBuffer(target,access)
target：当前绑定缓冲区对象的数据存储
accrss: GL_READ_ONLY
        GL_WRITE_ONLY
        GL_WRITE_READ_ONLY

glIsBuffer 查看缓冲区是否已被绑定
glDeleteBuffers 清空缓冲区对象
glUnmapBuffer(target) 对数据存储访问之后，调用取消对这个缓冲区的映射

#include "header.h"	

#define VERTICES 0
#define COLOR 1
#define INDICES 2
#define NUM_BUFFER 3
GLuint buffers[NUM_BUFFER];
float quard=0;

 GLfloat vertices[][3]={{0,0,50},//0
{100,0,50},//1
{100,100,50},//2
{0,100,50},//3
{0,0,-50},//4
{100,0,-50},//5
{100,100,-50},//6
{0,100,-50}//7
};
 GLfloat colors[][3]={{1.0,0.2,0.2}, {0.2,0.2,1.0}, {0.8,1.0,0.2}, {0.75,0.75,0.75}, {0.35,0.35,0.35}, {0.5,0.5,0.5}, {0.3,0.4,0.5}, {0.5,0.6,0.7}};
GLubyte indices[][4]={{3,2,1,0},{7,6,5,4},{7,4,0,3},{6,5,1,2},{7,3,2,6},{0,4,5,1}};



void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
	glLoadIdentity();
	glRotatef(quard,1,1,0);
	glDrawElements(GL_QUADS,24,GL_UNSIGNED_BYTE,0);
	glFlush();
	glutSwapBuffers();
	

}
void rotate()
{
	quard+=0.1;
	glutPostRedisplay();
}

void mouse(int button,int state,int x,int y)
{
	switch(button)
	{
	case GLUT_LEFT_BUTTON:
		if(GLUT_DOWN==state)
		{
			glutIdleFunc(rotate);
		}else
		{
			//glutIdleFunc(0);
		}
	}
}



void init()
{
	

	glClearColor(0.0,1.0,0.0,0.0);
	glClearDepth(1.0);
	glViewport(0,0,600,480);


	glEnable(GL_DEPTH_TEST);
	glDepthFunc(GL_LEQUAL);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();

	glOrtho(-300,300,-100,380,-100,100);
	glMatrixMode(GL_MODELVIEW);

	glewInit();
	glGenBuffers(NUM_BUFFER,buffers);
	glBindBuffer(GL_ARRAY_BUFFER,buffers[VERTICES]);
	glBufferData(GL_ARRAY_BUFFER,sizeof(vertices),vertices,GL_STATIC_DRAW);
	glVertexPointer(3,GL_FLOAT,0,0);
	glEnableClientState(GL_VERTEX_ARRAY);

	glBindBuffer(GL_ARRAY_BUFFER,buffers[COLOR]);
	glBufferData(GL_ARRAY_BUFFER,sizeof(colors),colors,GL_STATIC_DRAW);
	glColorPointer(3,GL_FLOAT,0,0);
	glEnableClientState(GL_COLOR_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(GLUT_DOUBLE|GLUT_RGB);

	glutInitWindowSize(600,480);
	glutInitWindowPosition(100,100);
	glutCreateWindow("缓冲区对象");

	init();

	glutDisplayFunc(display);
	glutMouseFunc(mouse);
	glutMainLoop();



	return 0;
}