如何复制剪切的HTML画布区域的内容？

Question

我正在尝试复制剪裁画布区域的内容。我正在使用onmousemove监听器捕获给定区域，并希望在onclick事件发生时复制其内容：

    var started = false;
    editor_canvas.onmousemove = function (e) {
        e = e || window.event;
        var x = event.pageX;
        var y = event.pageY;
        if (!started) {
            editor_context.beginPath();
            editor_context.moveTo(x, y);
            started = true;
            return;
        }

        var rect = editor_canvas.getBoundingClientRect();
        x = x - rect.left;
        y = y - rect.top;

        editor_context.lineWidth = 5;
        editor_context.strokeStyle = 'red';
        editor_context.lineTo(x, y);
        editor_context.stroke();
    };

    editor_canvas.onclick = function(e) {

        editor_context.clip();
    }

JSFiddle：http://jsfiddle.net/0nn78uxr/