convert and scale png files to svg files with cairo

png2svg.c

#include <cairo.h>
#include <cairo-svg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libgen.h>

// gcc -g png2svg.c -lm `pkg-config --cflags --libs cairo` -o png2svg

void strdecode(char *target, const char *needle, const char *replacement) {
    char buffer[1024] = { 0 };
    char *insert_point = &buffer[0];
    const char *tmp = target;
    size_t needle_len = strlen(needle);
    size_t repl_len = strlen(replacement);

    while (1) {
        const char *p = strstr(tmp, needle);
        if (p == NULL) {
            strcpy(insert_point, tmp);
            break;
        }
        memcpy(insert_point, tmp, p - tmp);
        insert_point += p - tmp;
        memcpy(insert_point, replacement, repl_len);
        insert_point += repl_len;
        tmp = p + needle_len;
    }
    strcpy(target, buffer);
}

int main(int argc, char* argv[]) {
    
    if (argc < 1) {
        fprintf(stdout, "usage: %s name.png scalefactor\n", basename(argv[0]));
        return 1;
    }
    cairo_surface_t *getpng = cairo_image_surface_create_from_png (argv[1]);
    int width = cairo_image_surface_get_width(getpng);
    int height = cairo_image_surface_get_height(getpng);
    double sx = 1.0;
    if (argc > 2) {
        sx = atof(argv[2]);
    }
    char svg_file[80];
    
    sprintf(svg_file, basename(argv[1]));
    strdecode(svg_file, ".png", ".svg");
    fprintf(stderr, "%s\n",svg_file);
    cairo_surface_t *frame = cairo_svg_surface_create(svg_file, width*sx, height*sx);
    cairo_t *crf = cairo_create(frame);
    cairo_scale(crf, sx, sx);
    cairo_set_source_surface(crf, getpng, 0, 0);
    cairo_paint(crf);
    cairo_surface_flush(frame);
    cairo_destroy(crf);
    cairo_surface_destroy(getpng);
    cairo_surface_destroy(frame);
    return 0;
}