canvas画布实现手写签名效果

最近项目中涉及到移动端手写签名的功能需求，将实现代码记录于此，供小伙伴们参考指摘哦~

HTML代码：

<!--手写区-->
        <div class="mSign_signMark_box">
            <div class="mSign_signMark_write_box">
                <div id="mSign_signMark_signature_pad" class="mSign_signMark_body_box">
                    <div class="mSign_signMark_body">
                        <span  class="mSign_signMark_clear_out">
                            <img src="../images/mCommon_basicIcon_deleteRed.png">
                        </span>
                        <p>手写区</p>
                        <canvas id="mSign_signMark_canvas"></canvas>
                    </div>
                </div>
            </div>
        </div>
        <!--手写区 end-->
        <!--底部按钮-->
        <div class="mSign_signMark_footer">
            <span id="mSign_signMark_clear_out" class="mSign_signMark_footer_can