Cairo straight operator function

#include <cairo.h>

int main (int argc, char *argv[])
{

    float alpha=0.65;
    float alpha_circle=0.8;

    cairo_surface_t *surface;
    cairo_t* cr;
    surface = cairo_image_surface_create(CAIRO_FORMAT_ARGB32, 480, 270);
    cr=cairo_create(surface);

    // Draw Circle
    cairo_save(cr);
    cairo_set_source_rgba(cr, 1.0, 0.5, 0.5, 1.0);
    cairo_move_to(cr, 140.0+70.0, 117.0);
    cairo_arc(cr, 140.0, 117.0, 70.0, 0.0, 2*3.14159);
    cairo_clip(cr);
    cairo_paint_with_alpha(cr, alpha_circle);
    cairo_restore(cr);

    //Prepare rectangle
    cairo_save(cr);
    cairo_set_source_rgba(cr, 0.26, 1.0, 1.0, 1.0);
    cairo_rectangle(cr, 164.0, 114.0, 186.0, 103.0);
    cairo_clip(cr);

    // Draw the surface over itself with 1.0-alpha
    cairo_surface_t* dest=cairo_surface_reference(cairo_get_target(cr));
    cairo_surface_flush(dest);
    cairo_t *destcr=cairo_create(dest);
    cairo_set_source_surface(destcr, dest, 0, 0);
    cairo_set_operator(destcr, CAIRO_OPERATOR_SOURCE);
    cairo_paint_with_alpha(cr, 1.0-alpha);
    cairo_surface_mark_dirty(dest);
    cairo_surface_destroy(dest);
    cairo_destroy(destcr);

    // Effectively draw the retangle
    cairo_set_operator(cr, CAIRO_OPERATOR_OVER);
    cairo_paint_with_alpha(cr, alpha);

    cairo_restore(cr);
    cairo_destroy(cr);

    cairo_surface_write_to_png(surface, "straight-cairo-full.png");
    cairo_surface_destroy(surface);

    return 0;
}