/* cloud1.c - Don Yang (uguu.org)

   09/26/09
                                                                           */

#include<stdio.h>
#include<stdlib.h>
#include<time.h>

#define DIVISION_COUNT  10
#define IMAGE_SIZE      (1 << DIVISION_COUNT)
#define INIT_RANGE      0.3
#define INIT_OFFSET     0.0
#define ROUGHNESS       0.9

#define RandomNumber()  (((double)rand()) / (double)RAND_MAX)

static double Image[IMAGE_SIZE + 1][IMAGE_SIZE + 1];

static void GenerateImage(void)
{
   int x, y, cx, cy, nx, ny, step;
   double displace_scale;

   /* Generate corners */
   Image[0][0] = INIT_OFFSET + INIT_RANGE * RandomNumber();
   Image[IMAGE_SIZE][0] = INIT_OFFSET + INIT_RANGE * RandomNumber();
   Image[0][IMAGE_SIZE] = INIT_OFFSET + INIT_RANGE * RandomNumber();
   Image[IMAGE_SIZE][IMAGE_SIZE] = INIT_OFFSET + INIT_RANGE * RandomNumber();

   /* Divide recursively */
   displace_scale = ROUGHNESS;
   for(step = IMAGE_SIZE; step > 1; step /= 2)
   {
      for(y = 0; y < IMAGE_SIZE; y = ny)
      {
         cy = y + step / 2;
         ny = y + step;
         for(x = 0; x < IMAGE_SIZE; x = nx)
         {
            cx = x + step / 2;
            nx = x + step;

            /* Add center point */
            Image[cy][cx] = (Image[y][x] +
                             Image[y][nx] +
                             Image[ny][x] +
                             Image[ny][nx]) / 4.0;

            /* Add edge points */
            Image[y][cx] = (Image[y][x] +
                            Image[y][nx] +
                            Image[cy][cx]) / 3.0;
            Image[cy][x] = (Image[y][x] +
                            Image[cy][cx] +
                            Image[ny][x]) / 3.0;
            Image[cy][nx] = (Image[y][nx] +
                             Image[cy][cx] +
                             Image[ny][nx]) / 3.0;
            Image[ny][cx] = (Image[cy][cx] +
                             Image[ny][x] +
                             Image[ny][nx]) / 3.0;

            /* Display newly added points */
            Image[y][cx] += (RandomNumber() - 0.5) * displace_scale;
            Image[cy][x] += (RandomNumber() - 0.5) * displace_scale;
            Image[cy][cx] += (RandomNumber() - 0.5) * displace_scale;
            Image[cy][nx] += (RandomNumber() - 0.5) * displace_scale;
            Image[ny][cx] += (RandomNumber() - 0.5) * displace_scale;
         }
      }
      displace_scale *= 0.5;
   }
}

/* Write image to stdout */
static void WriteImage()
{
   int x, y, c;

   printf("P2\n%d %d\n255\n", IMAGE_SIZE, IMAGE_SIZE);
   for(y = 0; y < IMAGE_SIZE; y++)
   {
      for(x = 0; x < IMAGE_SIZE; x++)
      {
         c = (int)(Image[y][x] * 255);
         if( c < 0 ) { (void)puts("0"); }
         else if( c > 255 ) { (void)puts("255"); }
         else { printf("%d\n", c); }
      }
   }
}

int main(void)
{
   srand((unsigned)time(NULL));
   GenerateImage();
   WriteImage();
   return 0;
}