A simple generator of Clifford attractors. Issue `make` to build it (requires `libnetpbm10-dev` on Debian).

clifford.c

#include <math.h>
#include <ppm.h>

int render_clifford(pixel **img, int width, int height, double a, double b, double c, double d)
{
    int i, x, y, max = 0;
    double x0 = 0.0, y0 = 0.0, x1, y1;

    for(y = 0; y < height; y++)
    {
        for(x = 0; x < width; x++)
        {
            img[y][x].r = 0;
            img[y][x].g = 0;
            img[y][x].b = 0;
        }
    }

    for(i = 0; i < 15 * width * height; ++i)
    {
        x1 = sin(a * y0) + c * cos(a * x0);
        y1 = sin(b * x0) + d * cos(b * y0);

        x0 = x1;
        y0 = y1;

        x = width * (1 + fabs(c) + x1) / (2.0 + 2.0 * fabs(c));
        y = height * (1 + fabs(d) + y1) / (2.0 + 2.0 * fabs(d));

        if(img[y][x].r < PGM_MAXMAXVAL)
        {
            img[y][x].r++;
            img[y][x].g++;
            img[y][x].b++;
        }

        if(img[y][x].r > max)
        {
            max = img[y][x].r;
        }
    }

    return max;
}

int main(int argc, char *argv[])
{
    double a, b, c, d;
    int width, height, max;
    pixel **img;

    if(argc != 7)
    {
        printf("Usage:\n  clifford width height a b c d > output.ppm\n");
        return 0;
    }

    width = atoi(argv[1]);
    height = atoi(argv[2]);
    a = atof(argv[3]);
    b = atof(argv[4]);
    c = atof(argv[5]);
    d = atof(argv[6]);

    ppm_init(&argc, argv);
    img = ppm_allocarray(width, height);

    max = render_clifford(img, width, height, a, b, c, d);

    ppm_writeppm(stdout, img, width, height, max, 0);
    ppm_freearray(img, height);

    return 0;
}

Makefile

CFLAGS=-lm -lnetpbm

clifford: clifford.c