// Extremely simple fault noise image generator
// Written by Jarmo (http://z0b.kapsi.fi)
// Public domain. No warranty of any kind, use at your own risk.
// Compile with: gcc -s -O2 -Wall -o fault[.exe] fault.cpp -std=c99

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// adjustable parameters
#define WIDTH           512
#define HEIGHT          512
#define NUM_ITERATIONS  4096
#define RANDOM_SEED     239398

// returns a random number on range [min, max]
static int randRange(const int min, const int max)
{
    return rand() % (max - min + 1) + min;
}

int main()
{
    uint8_t *noise = malloc(WIDTH * HEIGHT * sizeof(uint8_t));

    if (!noise) {
        printf("Out of memory\n");
        return 1;
    }

    // initial value is "in the middle"
    memset(noise, 128, WIDTH * HEIGHT);

    srand(RANDOM_SEED);

    printf("Generating noise...\n");

    for (size_t i = 0; i < NUM_ITERATIONS; i++) {
        // create a random line
        const float x1 = randRange(0, WIDTH - 1),
                    x2 = randRange(0, WIDTH - 1),
                    y1 = randRange(0, HEIGHT - 1),
                    y2 = randRange(0, HEIGHT - 1);

        // compute a normal for it (no need to normalize this)
        const float nx = y2 - y1,
                    ny = -(x2 - x1);

        uint8_t *dst = noise;

        for (size_t y = 0; y < HEIGHT; y++) {
            for (size_t x = 0; x < WIDTH; x++) {
                // dot product between the point and the line normal
                // tells us how far the point is from the line
                const float dist = (x - x1) * nx + (y - y1) * ny;

                if (dist < 0.0f) {
                    // decrement on the back side
                    if (*dst > 0)
                        (*dst)--;
                } else {
                    // increment on the front side
                    if (*dst < 255)
                        (*dst)++;
                }

                ++dst;
            }
        }
    }

    // save the image in TGA format
    printf("Saving the image...\n");

    FILE *f = fopen("fault_noise.tga", "wb");

    if (!f) {
        printf("Could not open the output file\n");
        free(noise);
        return 1;
    }

    const uint8_t header[18] =
    {
        0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        WIDTH & 0xFF, WIDTH >> 8, HEIGHT & 0xFF, HEIGHT >> 8,
        24,
        1 << 5
    };

    fwrite(header, 1, 18, f);

    const uint8_t *p = noise;

    for (size_t i = 0, j = WIDTH * HEIGHT; i < j; i++) {
        fputc(*p, f);
        fputc(*p, f);
        fputc(*p, f);
        p++;
    }

    fclose(f);
    free(noise);

    printf("Done\n");
    return 0;
}