Playing around with 2D graphics in C

smiley.c

#include <assert.h>
#include <stdio.h>

#include <cairo.h>

#define PIXEL_SIZE 50

void draw_to_file(const char *filename)
{
    assert(filename != NULL);

    cairo_surface_t *surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32,
        8 * PIXEL_SIZE, 8 * PIXEL_SIZE);
    cairo_t *cr = cairo_create(surface);

    // smiley :)
    const char pixels[] = {
        0b00111100,
        0b01000010,
        0b10100101,
        0b10000001,
        0b10100101,
        0b10011001,
        0b01000010,
        0b00111100
    };

    for (size_t row = 0; row < 8; row++) {
        for (size_t col = 0; col < 8; col++) {
            if (pixels[row] & (0b10000000 >> col)) {
                cairo_set_source_rgb(cr, 0.0, 0.0, 0.0); // black
            }
            else {
                cairo_set_source_rgb(cr, 1.0, 1.0, 1.0); // white
            }

            cairo_rectangle(cr, col * PIXEL_SIZE, row * PIXEL_SIZE,
                PIXEL_SIZE, PIXEL_SIZE);
            cairo_fill(cr);
        }
    }

    cairo_destroy(cr);
    cairo_surface_write_to_png(surface, filename);
    cairo_surface_destroy(surface);
}

/*
    $ brew install cairo
    $ cc -o smiley $(pkg-config --cflags --libs cairo) smiley.c
    $ ./smiley foo.png
    $ open foo.png
*/

int main(int argc, char *argv[])
{
    if (argc != 2) {
        printf("usage: %s <filename>\n", argv[0]);
        return 1;
    }

    draw_to_file(argv[1]);
    return 0;
}