OpenGL FBO (Frame Buffer Object) 帧缓冲对象

OpenGL中的几个重要缓冲系统有VBO(Vertex Buffer Object), PBO(Pixel Buffer Object),FBO(Frame Buffer Object)，其中VBO和PBO我们前面已经介绍了，主要采用的是glGenBuffers()来生成的服务器缓冲（GPU的内存），来实现高效绘制。FBO主要是用来做离屏渲染的，咱们的窗口系统有默认的帧缓冲对象（其对象值默认为0），如果想实现动态纹理的绘制，或者多屏的同时渲染，这时咱们可以使用帧缓冲对象，帧缓冲对象和像素缓冲对象是实现动态纹理的两个主要途径，使用帧缓冲对象的过程如下：

1.生成帧缓冲对象 glGenFrameBuffer()

2.绑定，使我们生成的帧缓冲对象作为当前的帧缓冲绘制对象。glBindFrameBuffer()

3.给帧缓冲区配置颜色、深度测试、模板测试缓冲区。其中颜色缓冲区可以有多个，颜色缓冲区主要是通过和纹理对象来结合使用，深度测试、模板测试缓冲区是通过帧缓冲区渲染对象来实现(glGenRenderBuffers() , glBindRenderBuffer() )

4.在绑定好的当前帧缓冲区上进行绘制。

5.将绑定到帧缓冲区对象的共享纹理取出，用于其他绘制操作。也可以直接通过glBlitFrameBuffer()来拷贝对应的渲染缓冲区，拷贝之前需要通过glBindFrameBuffer()操作将源帧缓冲区绑定为GL_READ_FRAMEBUFFER,将目的缓冲区绑定为GL_DRAW_FRAMEBUFFER(或则GL_FRAME_BUFFER)。

如下是我写的一个帧缓冲对象的示例。大家可以看看。

// framebuffer.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <vector>#include <string>#include <iostream>#include <GL/glew.h>#include <GL/glut.h>#pragma comment(lib, "glew32.lib")using namespace std;GLuint framebuffer = 0;GLuint texture = 0;enum {vertex_buffer = 0,coord_buffer,idx_buffer,vbo_buffer_size,};GLuint vboBuffer[vbo_buffer_size] = {0};void init(){ glGenFramebuffers(1,&framebuffer); glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);glGenTextures(1,&texture);glBindTexture(GL_TEXTURE_2D, texture);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);glTexImage2D(GL_TEXTURE_2D,0,GL_RGB,100,100,0,GL_RGB, GL_UNSIGNED_BYTE, 0);glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);std::cout<<glGetError()<<std::endl;assert(GLEW_NO_ERROR == glGetError());GLenum r = glCheckFramebufferStatus(GL_FRAMEBUFFER);if (r != GL_FRAMEBUFFER_COMPLETE)std::cout<<"r="<<r;float vertex[][3] = {{-4,-4,0},{-4,4,0},{4,4,0},{4,-4,0}};float coord[][2] ={{0,0},{0,1},{1,1},{1,0},};GLubyte index[] = {0,1,2,3};glGenBuffers(vbo_buffer_size, vboBuffer);glBindBuffer(GL_ARRAY_BUFFER, vboBuffer[vertex_buffer]);glBufferData(GL_ARRAY_BUFFER,sizeof(float)*4*3,vertex, GL_STATIC_DRAW);glVertexPointer(3,GL_FLOAT,0,0);glBindBuffer(GL_ARRAY_BUFFER, vboBuffer[coord_buffer]);glBufferData(GL_ARRAY_BUFFER,sizeof(float)*4*2,coord, GL_STATIC_DRAW);glTexCoordPointer(2,GL_FLOAT,0,0);glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vboBuffer[idx_buffer]);glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLubyte)*4, index,GL_STATIC_DRAW);glEnableClientState(GL_VERTEX_ARRAY);glEnableClientState(GL_TEXTURE_COORD_ARRAY);glBindTexture(GL_TEXTURE_2D, 0);glBindBuffer(GL_ARRAY_BUFFER, 0);glEnable(GL_TEXTURE_2D);GLenum fff = glGetError();assert(glGetError() == 0);}void display(){ glBindFramebuffer(GL_FRAMEBUFFER, framebuffer); glPushAttrib(GL_ALL_ATTRIB_BITS); glPushMatrix(); glClearColor(1.0f,1.0f,1.0,1.0f); glViewport(0,0,100,100); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-5,5,-5,5,-5,5); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glClear(GL_COLOR_BUFFER_BIT); glColor3f(0,0,1); glRectf(-5,-5,0,5);glColor3f(1,1,0);glRectf(0,-5, 5,5); glPopMatrix(); glPopAttrib();//glBindFramebuffer(GL_READ_FRAMEBUFFER, framebuffer);glBindFramebuffer(GL_FRAMEBUFFER, 0); glPushAttrib(GL_ALL_ATTRIB_BITS);glPushMatrix();glBindTexture(GL_TEXTURE_2D,texture);glClearColor(1.0f, 1.0f, 1.0f, 1.0f);glViewport(0,0,100,100); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(-5,5,-5,5,-5,5); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glClear(GL_COLOR_BUFFER_BIT); glColor4f(1.0f, 1.0f, 1.0f, 1.0f); glDrawArrays(GL_TRIANGLE_FAN, 0, 4);//glBlitFramebuffer(0,0,100,100,0,0,100,100,GL_COLOR_BUFFER_BIT, GL_NEAREST);glPopMatrix();glPopAttrib();glBindTexture(GL_TEXTURE_2D, 0);glutSwapBuffers();}void reshape(int w, int h){}int _tmain(int argc, _TCHAR* argv[]){std::vector<int> bits;std::vector<int> enums;std::vector<std::string> types;glutInit(&argc, argv);glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA);glutInitWindowSize(100,100);glutInitWindowPosition(100,100);glutCreateWindow("Frame Buffer Object");assert(glewInit() == 0);init();glutReshapeFunc(reshape);glutDisplayFunc(display);glutMainLoop();getchar();return 0;}

运行效果图：