#include <GL/gl.h>
#include <GL/glext.h>
#include <GL/glut.h>
#include <stdio.h>
#include <assert.h>

GLuint fb,depth_rb,tex;

#define CHECK_FRAMEBUFFER_STATUS() \
{\
 GLenum status; \
 status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT); \
 fprintf(stderr, "%x\n", status);\
 switch(status) { \
 case GL_FRAMEBUFFER_COMPLETE_EXT: \
   fprintf(stderr,"framebuffer complete!\n");\
   break; \
 case GL_FRAMEBUFFER_UNSUPPORTED_EXT: \
   fprintf(stderr,"framebuffer GL_FRAMEBUFFER_UNSUPPORTED_EXT\n");\
    /* you gotta choose different formats */ \
   assert(0); \
   break; \
 case GL_FRAMEBUFFER_INCOMPLETE_ATTACHMENT_EXT: \
   fprintf(stderr,"framebuffer INCOMPLETE_ATTACHMENT\n");\
   break; \
 case GL_FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT_EXT: \
   fprintf(stderr,"framebuffer FRAMEBUFFER_MISSING_ATTACHMENT\n");\
   break; \
 case GL_FRAMEBUFFER_INCOMPLETE_DIMENSIONS_EXT: \
   fprintf(stderr,"framebuffer FRAMEBUFFER_DIMENSIONS\n");\
   break; \
 case GL_FRAMEBUFFER_INCOMPLETE_DUPLICATE_ATTACHMENT_EXT: \
   fprintf(stderr,"framebuffer INCOMPLETE_DUPLICATE_ATTACHMENT\n");\
   break; \
 case GL_FRAMEBUFFER_INCOMPLETE_FORMATS_EXT: \
   fprintf(stderr,"framebuffer INCOMPLETE_FORMATS\n");\
   break; \
 case GL_FRAMEBUFFER_INCOMPLETE_DRAW_BUFFER_EXT: \
   fprintf(stderr,"framebuffer INCOMPLETE_DRAW_BUFFER\n");\
   break; \
 case GL_FRAMEBUFFER_INCOMPLETE_READ_BUFFER_EXT: \
   fprintf(stderr,"framebuffer INCOMPLETE_READ_BUFFER\n");\
   break; \
 case GL_FRAMEBUFFER_BINDING_EXT: \
   fprintf(stderr,"framebuffer BINDING_EXT\n");\
   break; \
/* 
 case GL_FRAMEBUFFER_STATUS_ERROR_EXT: \
   fprintf(stderr,"framebuffer STATUS_ERROR\n");\
   break; \
*/ \
 default: \
   /* programming error; will fail on all hardware */ \
   assert(0); \
 }\
}


int imageWinWidth = 256;
int imageWinHeight = 256;

void reshape(int w, int h)
{
  glClearColor (0.0, 0.0, 0.0, 0.0);
  glViewport(0, 0, (GLsizei) w, (GLsizei) h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();

  glFrustum(0.0, 1.0,  1.0, 0.0,   1.0,   100.0);
  gluLookAt(0.0,0.0,0.0,  0.0, 0.0,  -1.0,   0.0, 1.0, 0.0);

  glMatrixMode(GL_MODELVIEW);

  glLoadIdentity();
  glutPostRedisplay();
}

static GLenum errCode;
const GLubyte *errString;

void errcheck() {

  if ((errCode = glGetError()) != GL_NO_ERROR) {
    errString = gluErrorString(errCode);
    fprintf (stderr, "OpenGL Error: %s\n", errString);
    exit(1);
  }

}


void myIdle(){
  glutPostRedisplay();
}

void keyboard (unsigned char key, int x, int y)
{
   switch (key) {
      case 27:
         exit(0);
         break;
      default:
         break;
   }
}

void MouseFunc( int button, int state, int x, int y)
{
  switch(button) {
    case GLUT_LEFT_BUTTON :
      break;
    case GLUT_RIGHT_BUTTON :
      break;
  }
}


void render_redirect() {

  //bind the FBO, and the associated texture.
  glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);

  // draw a scene.  the results are being 
  // written into the associated texture,'tex'
  glClearColor(0.0, 0.0, 1.0, 1.0);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glColor4f( 1.0, 1.0, 1.0, 1.0);
  glLineWidth(5.0);
  glBegin(GL_LINES);
    glColor4f( 1.0, 1.0, 1.0, 1.0);
    glVertex3f( 0.0, 0.0, -1.0);
    glVertex3f( 1.0, 1.0, -1.0);
  glEnd();

  // 'unbind' the FBO. things will now be drawn to screen as usual
  glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);


  glClearColor(0.0, 1.0, 0.0, 1.0);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glColor3f(1.0, 1.0, 1.0); 
  glEnable(GL_TEXTURE_RECTANGLE_NV);
  glBindTexture(GL_TEXTURE_RECTANGLE_NV, tex);
  // draw the 'tex' texture containing the framebuffer rendered drawing.
  glBegin(GL_QUADS); 

    glTexCoord2f(0, 0);
    glVertex3f(0.0, 0.0, -1.0);

    glTexCoord2f(0, 256);
    glVertex3f(0.0, .5, -1.0);

    glTexCoord2f(256,256);
    glVertex3f(.5,.5, -1.0);

    glTexCoord2f(256,0);
    glVertex3f(.5, 0.0, -1.0);
  glEnd();
  glDisable(GL_TEXTURE_RECTANGLE_NV);

  glutSwapBuffers();
}

int main(int argc, char *argv[] )  {

   glutInit( &argc, argv );
   glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
   glutInitWindowSize(imageWinWidth, imageWinHeight);
   glutCreateWindow(argv[0]);


   //gen the frambuffer object (FBO), similar manner as  a texture
   glGenFramebuffersEXT(1, &fb);
   errcheck();
   // make a texture
   glGenTextures(1, &tex);              // texture

   //bind the framebuffer, fb, so operations will now occur on it
   glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);

   // initialize texture that will store the framebuffer image
   glBindTexture(GL_TEXTURE_RECTANGLE_NV, tex);
   glTexImage2D(GL_TEXTURE_RECTANGLE_NV, 0, GL_RGBA, 256,256, 0,
                GL_RGBA, GL_UNSIGNED_BYTE,NULL);
   errcheck();

   // bind this texture to the current framebuffer obj. as 
   // color_attachement_0 
   glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT,
              GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_RECTANGLE_NV, tex, 0);
   errcheck();

   //see if everything is OK
   CHECK_FRAMEBUFFER_STATUS()

   //'unbind' the frambuffer object, so subsequent drawing ops are not
   // drawn into the FBO. 
   // '0' means "windowing system provided framebuffer
   glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

   glutDisplayFunc(render_redirect);
   glutIdleFunc(myIdle);
   glutReshapeFunc(reshape);
   glutKeyboardFunc(keyboard);
   glutMouseFunc(MouseFunc);
   glutMainLoop();
   return 0;
}