/******************************************************************************
* FILE:   simple_image.cc
*         A simple example of generating an image file.
*
* Author: Dana Vrajitoru, IUSB
* Class:  C481 B581 Computer Graphics
******************************************************************************/

#include <fstream>
using namespace std;

const int WIDTH = 200, HEIGHT = 200;

// prototypes
void Set_pixel(short r, short g, short b, int x, int y);
void Write_ppm(char *filename);
void Make_vertical_gradient(short r1, short g1, short b1, 
			    short r2, short g2, short b2);

// The image itself as a global object
short r_matrix[HEIGHT][WIDTH], 
      g_matrix[HEIGHT][WIDTH], 
      b_matrix[HEIGHT][WIDTH];

int main() { 
  //Fill the image with a horizontal gradient between red and blue.
  Make_vertical_gradient(255, 0, 0, 0, 0, 255);
  Write_ppm("red2blue.ppm");
}

// Fill the image with a horizontal gradient.
void Make_vertical_gradient(short r1, short g1, short b1, 
			    short r2, short g2, short b2)
{
  short r, g, b;
  for (int y=0; y<HEIGHT; y++)
    for (int x=0; x<WIDTH; x++) {
      r = (short) ( r1 + (r2-r1) * float(x) / WIDTH);
      g = (short) ( g1 + (g2-g1) * float(x) / WIDTH);
      b = (short) ( b1 + (b2-b1) * float(x) / WIDTH);
      Set_pixel(r, g, b, x, y);
    }
}

// Set the color of one pixel.
void Set_pixel(short r, short g, short b,
	       int x, int y)
{
  r_matrix[y][x] = r;
  g_matrix[y][x] = g;
  b_matrix[y][x] = b;
}

// Write the image as a ppm file.
void Write_ppm(char *filename)
{
  ofstream fout(filename);
  if (fout) {
    fout << "P3" << endl << "# CREATOR: Dana Vrajitoru" << endl;
    fout << WIDTH << " " << HEIGHT << endl << 255 << endl;
    for (int y=0; y<HEIGHT; y++)
      for (int x=0; x<WIDTH; x++) {
        fout << r_matrix[y][x] << endl
              << g_matrix[y][x] << endl
              << b_matrix[y][x] << endl;
      }
    fout.close();
  }
}