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

// define texture width = N and height = M and v = 4*N*M
#define N 640
#define M 480
#define v 4*N*M

int main( int argc, char **argv )
{
    int i;

    // create three pointers to store our vectors x, y, z
    float * x = ( float * ) malloc( v * sizeof( float ) );
    float * y = ( float * ) malloc( v * sizeof( float ) );
    float * z = ( float * ) malloc( v * sizeof( float ) );

    // fill up y and z with some data
    for ( i = 0; i < v; i++ )
    {
        x[i] = (float)( i / 10.0 );
        y[i] = (float)( i / 20.0 );
    }
    
    // set up glut and glew
    glutInit( &argc, argv );
    glutCreateWindow( "add" );
    glewInit(  );
    
    // some obligatory OpenGL settings
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity(  );
    gluOrtho2D( 0.0, N, 0.0, M );
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity(  );
    glViewport( 0, 0, N, M );

    // set up Cg context and profile
    CGcontext context = cgCreateContext(  );
    CGprofile profile = cgGLGetLatestProfile( CG_GL_FRAGMENT );
    cgGLSetOptimalOptions( profile );
   
    // create fragment program add from add.cg
    CGprogram program = cgCreateProgramFromFile( context, CG_SOURCE, "add.cg", profile, "add", 0 );
    cgGLLoadProgram( program );

    // create frame buffer object
    GLuint fb;
    glGenFramebuffersEXT( 1, &fb );
    glBindFramebufferEXT( GL_FRAMEBUFFER_EXT, fb );
    
    // create texture ids for x, y, z
    GLuint tex_x, tex_y, tex_z;
    glGenTextures( 1, &tex_x );
    glGenTextures( 1, &tex_y );
    glGenTextures( 1, &tex_z );

    // bind texture x
    glBindTexture( GL_TEXTURE_RECTANGLE_ARB, tex_x );
    
    // set texture parameters for x
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_S, GL_CLAMP );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_T, GL_CLAMP );
    
    // actually create texture x
    glTexImage2D( GL_TEXTURE_RECTANGLE_ARB, 0, GL_FLOAT_RGBA32_NV, M, N, 0, GL_RGBA, GL_FLOAT, 0 );
    
    // attach texture x
    glFramebufferTexture2DEXT( GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_RECTANGLE_ARB, tex_x, 0 );
    
    // transfer data x to texture x
    glTexSubImage2D( GL_TEXTURE_RECTANGLE_ARB, 0, 0, 0, M, N, GL_RGBA, GL_FLOAT, x );

    // do everything for y as well
    glBindTexture( GL_TEXTURE_RECTANGLE_ARB, tex_y );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_S, GL_CLAMP );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_T, GL_CLAMP );
    glTexImage2D( GL_TEXTURE_RECTANGLE_ARB, 0, GL_FLOAT_RGBA32_NV, M, N, 0, GL_RGBA, GL_FLOAT, 0 );
    glFramebufferTexture2DEXT( GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_RECTANGLE_ARB, tex_y, 0 );
    glTexSubImage2D( GL_TEXTURE_RECTANGLE_ARB, 0, 0, 0, M, N, GL_RGBA, GL_FLOAT, y );

    // do everything for z as well, except for transfering data to it
    glBindTexture( GL_TEXTURE_RECTANGLE_ARB, tex_z );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_S, GL_CLAMP );
    glTexParameteri( GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_T, GL_CLAMP );
    glTexImage2D( GL_TEXTURE_RECTANGLE_ARB, 0, GL_FLOAT_RGBA32_NV, M, N, 0, GL_RGBA, GL_FLOAT, 0 );
  
    // specify the two arguments x and y of the program add
    cgGLSetTextureParameter( cgGetNamedParameter( program, "x" ), tex_x );
    cgGLEnableTextureParameter( cgGetNamedParameter( program, "x" ) );
    
    cgGLSetTextureParameter( cgGetNamedParameter( program, "y" ), tex_y );
    cgGLEnableTextureParameter( cgGetNamedParameter( program, "y" ) );

    // specify the outgoing texture to be z
    glFramebufferTexture2DEXT( GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_RECTANGLE_ARB, tex_z, 0 );
    glDrawBuffer( GL_COLOR_ATTACHMENT0_EXT );
   
    // tell Cg to use our profile and program
    cgGLEnableProfile( profile );
    cgGLBindProgram( program );
   
    // run the program
    glBegin( GL_QUADS );
    {
	glVertex2f( -M, -N );
	glVertex2f( M, -N );
	glVertex2f( M, N );
	glVertex2f( -M, N );
    }
    glEnd(  );
    
    // read back result from texture z
    glFramebufferTexture2DEXT( GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_RECTANGLE_ARB, tex_z, 0 );
    glReadBuffer( GL_COLOR_ATTACHMENT0_EXT );
    glReadPixels( 0, 0, M, N, GL_RGBA, GL_FLOAT, z );

    // now the result of z = x + y is pointed by pointer z, let's see the first couple of terms
    printf( "\nThese should be really equal, the first column is\n" );
    printf( "the result from the GPU the second is from the CPU:\n\n" );
    for( i = 0; i < 10; i++ )
    {
        printf( "%f = %f\n", z[i], x[i] + y[i] );
    }
    
    // do the clean up
    free( x );
    free( y );
    free( z );
    glDeleteTextures( 1, &tex_x );
    glDeleteTextures( 1, &tex_y );
    glDeleteTextures( 1, &tex_z );
    glDeleteFramebuffersEXT( 1, &fb );

    return 0;
}