OpenGL FBO渲染到纹理实例

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <GL/glew.h>
#include <GL/glut.h>


GLuint v,f,f2,p;
float lpos[4] = {1,0.5,1,0};
GLint loc;
GLint uvloc;
GLint samp;
GLint sach;
GLuint textureId; 
GLuint rboId;
GLuint fboId;
bool fboUsed;
float vertices[8] = {-2,2, 2,2, -2,-2, 2,-2};
float heights[4] = {2,2,-2,-2};
float uvm[8]={0,0,0,1,1,0,1,1};
char *textFileRead(char *fn) {


	FILE *fp;
	char *content = NULL;

	int count=0;

	if (fn != NULL) {
		fp = fopen(fn,"rt");

		if (fp != NULL) {
      
      fseek(fp, 0, SEEK_END);
      count = ftell(fp);
      rewind(fp);

			if (count > 0) {
				content = (char *)malloc(sizeof(char) * (count+1));
				count = fread(content,sizeof(char),count,fp);
				content[count] = '\0';
			}
			fclose(fp);
		}
	}
	return content;
}

int textFileWrite(char *fn, char *s) {

	FILE *fp;
	int status = 0;

	if (fn != NULL) {
		fp = fopen(fn,"w");

		if (fp != NULL) {
			
			if (fwrite(s,sizeof(char),strlen(s),fp) == strlen(s))
				status = 1;
			fclose(fp);
		}
	}
	return(status);
}
void changeSize(int w, int h) {

	// Prevent a divide by zero, when window is too short
	// (you cant make a window of zero width).
	if(h == 0)
		h = 1;

	float ratio = 1.0* w / h;

	// Reset the coordinate system before modifying
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	
	// Set the viewport to be the entire window
    glViewport(0, 0, w, h);

	// Set the correct perspective.
	gluPerspective(45,ratio,1,1000);
	glMatrixMode(GL_MODELVIEW);
gluLookAt(0.0,5.0,0.0, 
		      0.0,0.0,0.0,
			 1.0f,0.0f,0.0f);

}
float a =