jquery canvas generates posters with QR codes

In this paper, we share the specific code of jquery canvas poster with 2-dimensional code for your reference. The specific contents are as follows

Requirements: Click on the picture pop-up window to generate posters with 2D codes.

Related problems encountered:

1. The generated picture will be blurred and unclear.
2. There are differences in text position and font size between Apple and Android phones.

Introduce the required files

//jquery.js
<script type="text/javascript" src="https://apps.bdimg.com/libs/jquery/2.1.4/jquery.min.js"></script>
// Solve the problem that the generated picture is fuzzy and unclear 
<script src="/images/202010/hidpi-canvas.min.js"></script>

Generate poster pictures

<script>
    //  Execute code 
    $(function () {

        //   Pixel density   Without this code, the generated picture may be blurred 
        function getPixelRatio(context) {
            var backingStore = context.backingStorePixelRatio ||
                context.webkitBackingStorePixelRatio ||
                context.mozBackingStorePixelRatio ||
                context.msBackingStorePixelRatio ||
                context.oBackingStorePixelRatio ||
                context.backingStorePixelRatio || 1;
            return (window.devicePixelRatio || 1) / backingStore;
        };
        // Click event 
        $(".myImg").click(function () {
            $(".dialog").fadeIn();
            var dialogSrc = $(this).attr("src")
            var csrfToken = document.querySelector('meta[name="csrf-token"]').getAttribute('content');
            //2. Send a request 
            $.ajax({
                url: "xxxx",
                type: "post",
                dataType: 'json',
                headers: {
                    'X-CSRF-TOKEN': csrfToken
                }, // Set the request header 
                success: function (res) {
                    var canvas = document.createElement("canvas");
                    var context = canvas.getContext("2d");

                    var ratio = getPixelRatio(context)

                    canvas.width = 262 * ratio;
                    canvas.height = 450 * ratio;
                    context.rect(0, 0, canvas.width * ratio, canvas.height * ratio);
                    context.fillStyle = "#fff";
                    context.fill();

                    var myImage2 = new Image();
                    // Background map 
                    myImage2.src = dialogSrc
                    // Acquisition terminal 
                    var u = navigator.userAgent;
                    var isAndroid = u.indexOf('Android') > -1 || u.indexOf('Adr') > -1; //android Terminal 
                    var isiOS = !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/); //ios Terminal 
                    myImage2.onload = function () {
                        context.drawImage(myImage2, 0, 0, 262 * ratio, 450 * ratio);
                        // Text 
                        var text = res.data.company + ',' + res.data.sales;
                        var str = new Array();
                        str = text.split(",");
                        var uphight = 0
                        // Solve Apple phones and Android phones   Display difference between text position and font size 
                        for (var i = 0; i < str.length; i++) {
                            if (isAndroid) {
                                context.font = "12px Calibri";
                                context.fillText(str[i], 70, 390 + uphight)
        uphight += 20
                            }

                            if (isiOS) {
                                context.font = "20px Calibri";
                                context.fillText(str[i], 140, 450 * ratio - 120 + uphight)
        uphight += 40
                            }
                        }
                        var myImage = new Image();
                        //2 Dimension code picture 
                        myImage.src = res.data.wxcode
                        myImage.crossOrigin = 'Anonymous';
                        myImage.onload = function () {
                            context.drawImage(myImage, 30, 380 * ratio, 48 * ratio, 50 * ratio);
                            var base64 = canvas.toDataURL("image/jpeg", 1.0);
                            var img = document.getElementById('myPoster');
                            img.setAttribute('src', base64);
                        }
                    }
                },
                error: function (e) {
                    console.log('ajax Request an exception with the following exception information: ', e);
                }
            });
        });
        // Close the pop-up window 
        $(".close").click(function () {
            $(".dialog").fadeOut();
        })
    });
</script>