使用原生cavans把图片和文字生成一张新的图片并解决失真问题

*,body{
    margin: 0;
    padding: 0;
}
.operat input{
    position: absolute;
    top: 20rem;
    left: 7.6rem;
    width: 5rem;
    height: 3rem;
    line-height: 3rem;
    text-align: center;
    background: #f0f4fa;
    border: solid 1px #f0f4fa;
    font-size: 1.5rem;
    font-weight: bold;
}
.submit-btn{
    position: fixed;
    width: 10.95rem;
    height: 2.4rem;
    bottom: 10rem;
    right: 2rem;
    background: url("../images/poster/btn.png") no-repeat;
    background-size: 100% 100%;
    border: 0px solid transparent;
    z-index: 100;
}

图片分别是背景图和按钮图