SVG writer for polygons

// if the Polygon class name conflicts with a class in wingdi.h on Windows, use a namespace or change the name
class Polygon {
public:
    std::vector<Vector> vertices;
};

// saves a static svg file. The polygon vertices are supposed to be in the range [0..1], and a canvas of size 1000x1000 is created
    void save_svg(const std::vector<Polygon> &polygons, std::string filename, std::string fillcol = "none") {
        FILE* f = fopen(filename.c_str(), "w+");
        fprintf(f, "<svg xmlns = \"http://www.w3.org/2000/svg\" width = \"1000\" height = \"1000\">\n");
        for (int i=0; i<polygons.size(); i++) {
            fprintf(f, "<g>\n");
            fprintf(f, "<polygon points = \"");
            for (int j = 0; j < polygons[i].vertices.size(); j++) {
                fprintf(f, "%3.3f, %3.3f ", (polygons[i].vertices[j][0] * 1000), (1000 - polygons[i].vertices[j][1] * 1000));
            }
            fprintf(f, "\"\nfill = \"%s\" stroke = \"black\"/>\n", fillcol.c_str());
            fprintf(f, "</g>\n");
        }
        fprintf(f, "</svg>\n");
        fclose(f);
    }


// Adds one frame of an animated svg file. frameid is the frame number (between 0 and nbframes-1).
// polygons is a list of polygons, describing the current frame.
// The polygon vertices are supposed to be in the range [0..1], and a canvas of size 1000x1000 is created
    void save_svg_animated(const std::vector<Polygon> &polygons, std::string filename, int frameid, int nbframes) {
        FILE* f;
        if (frameid == 0) {
            f = fopen(filename.c_str(), "w+");
            fprintf(f, "<svg xmlns = \"http://www.w3.org/2000/svg\" width = \"1000\" height = \"1000\">\n");
            fprintf(f, "<g>\n");
        } else {
            f = fopen(filename.c_str(), "a+");
        }
        fprintf(f, "<g>\n");
        for (int i = 0; i < polygons.size(); i++) {
            fprintf(f, "<polygon points = \"");
            for (int j = 0; j < polygons[i].vertices.size(); j++) {
                fprintf(f, "%3.3f, %3.3f ", (polygons[i].vertices[j][0] * 1000), (1000-polygons[i].vertices[j][1] * 1000));
            }
            fprintf(f, "\"\nfill = \"none\" stroke = \"black\"/>\n");
        }
        fprintf(f, "<animate\n");
        fprintf(f, "    id = \"frame%u\"\n", frameid);
        fprintf(f, "    attributeName = \"display\"\n");
        fprintf(f, "    values = \"");
        for (int j = 0; j < nbframes; j++) {
            if (frameid == j) {
                fprintf(f, "inline");
            } else {
                fprintf(f, "none");
            }
            fprintf(f, ";");
        }
        fprintf(f, "none\"\n    keyTimes = \"");
        for (int j = 0; j < nbframes; j++) {
            fprintf(f, "%2.3f", j / (double)(nbframes));
            fprintf(f, ";");
        }
        fprintf(f, "1\"\n   dur = \"5s\"\n");
        fprintf(f, "    begin = \"0s\"\n");
        fprintf(f, "    repeatCount = \"indefinite\"/>\n");
        fprintf(f, "</g>\n");
        if (frameid == nbframes - 1) {
            fprintf(f, "</g>\n");
            fprintf(f, "</svg>\n");
        }
        fclose(f);
    }