图片 文字合成

//图片文字合成
synthesis(type, text, myId) {
    let imgURL;
    switch (type) {
        case '1.html' :
            imgURL = 'static/images/1.png';
            break;
        case '2.html' :
            imgURL = 'static/images/2.png';
            break;
        case '3.html' :
            imgURL = 'static/images/3.png';
            break;
     
        default:
            imgURL = 'static/images/4.png';
            break;
    }
    let img;
    document.getElementById(myId).height = 0;
    document.getElementById(myId).height = 100;
    var mainCtx = document.getElementById(myId).getContext("2d");

    // 创建一个待合成图片
    var starImg = new Image();
    starImg.src = imgURL;
    starImg.onload = function () {
        //图片绘制
        mainCtx.drawImage(starImg, 31, 18, 38, 32);
        //文本,图片合成
        mainCtx.font = "normal 500 14px Arial";
        mainCtx.fillStyle = "#073061";
        mainCtx.textAlign = "center";
        mainCtx.fillText(text, 50, 70, 80);
        //导出合成图片
        var mycanvas = document.getElementById(myId);
        img = mycanvas.toDataURL("image/jpeg", 1.0);
    };
}