 - canvas_rect.left, e.clientY - canvas_rect.top, false);
    }, false);

    synthesis.addEventListener('mouseleave', function(e){
        synthesis_draw(0, 0, false);
    }, false);
}

function synthesis_draw(client_x, client_y, do_guides){
    synthesis = document.getElementById("synthesis");
    var synthesis_context = synthesis.getContext("2d");
    synthesis_context.font = "16px sans-serif";
    // background
    synthesis_context.fillStyle="#eeeeee";
    synthesis_context.fillRect(0, 0, w, h);

    /