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

static texSize = 4;
static GLenum textarget = GL_TEXTURE_2D;
static GLenum texinternalformat = GL_RGBA_FLOAT32_ATI;


int main(int argc, char **argv) {
    // declare texture size, the actual data will be a vector 
    // of size texSize*texSize*4
    // create test data and fill arbitrarily
    float* data = (float*)malloc(4*texSize*texSize*sizeof(float));
    float* result = (float*)malloc(4*texSize*texSize*sizeof(float));
    for (int i=0; i<texSize*texSize*4; i++)
        data[i] = i+1.0;
    // set up glut to get valid GL context and 
    // get extension entry points
    glutInit (&argc, argv);
    glutCreateWindow("TEST1");
    glewInit();
    // viewport transform for 1:1 pixel=texel=data mapping
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0.0,texSize,0.0,texSize);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glViewport(0,0,texSize,texSize);
    // create FBO and bind it (that is, use offscreen render target)
    GLuint fb;
    glGenFramebuffersEXT(1,&fb); 
    glBindFramebufferEXT(GL_FRAMEBUFFER_EXT,fb);
    // create texture
    GLuint tex;
    glGenTextures (1, &tex);
    glBindTexture(textarget,tex);
    // set texture parameters
    glTexParameteri(textarget, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(textarget, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(textarget, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameteri(textarget, GL_TEXTURE_WRAP_T, GL_CLAMP);
    // define texture with floating point format
    glTexImage2D(textarget,0,texinternalformat,texSize,texSize,0,GL_RGBA,GL_FLOAT,0);
    // attach texture
    glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, textarget,tex,0);
    // transfer data to texture
	glDrawBuffer(GL_COLOR_ATTACHMENT0_EXT);
	glRasterPos2i(0,0);
	glDrawPixels(texSize,texSize,GL_RGBA,GL_FLOAT,data);
    // and read back
    glReadBuffer(GL_COLOR_ATTACHMENT0_EXT);
    glReadPixels(0, 0, texSize, texSize,GL_RGBA,GL_FLOAT,result);
    // print out results
    printf("Data before roundtrip:\n");
    for (int i=0; i<texSize*texSize*4; i++)
        printf("%f\n",data[i]);
    printf("Data after roundtrip:\n");
    for (int i=0; i<texSize*texSize*4; i++)
        printf("%f\n",result[i]);
    // clean up
    free(data);
    free(result);
    glDeleteFramebuffersEXT (1,&fb);
    glDeleteTextures (1,&tex);
    return 0;
}