javascript - 在 Javascript 中转换和插入 Base64 数据到 Canvas

Question

我得到一个数据缓冲区，表示 Base64 格式的图像。 我得到的数据(以base64表示图像)(部分数据)

193,109,51,74,182,71,212,38,78,62,211,48,81,145,244,39,244,250,215,192,113,46,101,136,203,149,44,6,90,147,197,215,109,66,251,69,47,138,111,202,43,239,122,45,108,125,22,6,149,44, 84,103,136,198,74,212,41,171,203,188,187,69,121,183,255,0,7,75,156,191,140,​​190,45,181,219,141,43,195,214,107,30,129,3,145,38,110,60,135,185,35,130,119,4,108,244,238,0,227,3,140,​​86,85,237,134,149,241,3,69,158,251,71,134,93,31,88,211, 72,82,1,30,100,76,70,65,12,9,12,141,207,94,184,32,140,​​215,45,47,196,111,130,177,187,34,120,79,197,65,84,224,8,175,93,20,929,120,929,1206 85,141,47,227,159,195,111,11,219,223,46,133,225,175,17,91,73,120,170,178,189,196,137,49,96,185,218,50,247,44,64,27,155,167,173,123,252,61,144,97,242,8,63,102,156,234,207,227,169,43,115,77,245,230,119,122,111,104,173,23,78,167,204,103,121,165,108,217,46,88,184,40,124... ..

解码成功

现在我尝试将图像添加到我的 Canvas ，但没有成功，如下所示:

function fillCanvasImage(x, y, width, height, image, pageID) {
    if (image == "")
        return;

    var canvas = document.getElementById("AppPmainCanvas" + pageID);

    if (canvas && canvas.getContext) {
        var context = canvas.getContext('2d');
        if (context) {
            context.clearRect(0, 0, canvas.width, canvas.height);
            var img = new Image();
            img.src = base64_decode(image);
            //img.onload = function () {
                context.drawImage(img, 0, 0, canvas.width, canvas.height);
            //}
        }
    }
}

我通过以下方式转换数据形式的 base64:

function base64_decode(data) {
    var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    var o1, o2, o3, h1, h2, h3, h4, bits, i = 0,
        ac = 0,
        dec = "",
        tmp_arr = [];

    if (!data) {
        return data;
    }

    data += '';

    do { // unpack four hexets into three octets using index points in b64
        h1 = b64.indexOf(data.charAt(i++));
        h2 = b64.indexOf(data.charAt(i++));
        h3 = b64.indexOf(data.charAt(i++));
        h4 = b64.indexOf(data.charAt(i++));

        bits = h1 << 18 | h2 << 12 | h3 << 6 | h4;

        o1 = bits >> 16 & 0xff;
        o2 = bits >> 8 & 0xff;
        o3 = bits & 0xff;

        if (h3 == 64) {
            tmp_arr[ac++] = String.fromCharCode(o1);
        } else if (h4 == 64) {
            tmp_arr[ac++] = String.fromCharCode(o1, o2);
        } else {
            tmp_arr[ac++] = String.fromCharCode(o1, o2, o3);
        }
    } while (i < data.length);

    dec = tmp_arr.join('');
    dec = utf8_decode(dec);

    return dec;
};

// private method for UTF-8 decoding
function utf8_decode(utftext) {
    var string = "";
    var i = 0;
    var c = 0,
        c1 = 0,
        c2 = 0;

    while (i < utftext.length) {
        c = utftext.charCodeAt(i);

        if (c < 128) {
            string += String.fromCharCode(c);
            i++;
        } else if ((c > 191) && (c < 224)) {
            c1 = utftext.charCodeAt(i + 1);
            string += String.fromCharCode(((c & 31) << 6) | (c1 & 63));
            i += 2;
        } else {
            c1 = utftext.charCodeAt(i + 1);
            c2 = utftext.charCodeAt(i + 2);
            string += String.fromCharCode(((c & 15) << 12) | ((c1 & 63) << 6) | (c2 & 63));
            i += 3;
        }
    }

    return string;
};

它不起作用，我执行以下操作: 在我的服务器端，我将图像转换如下:

public static string BitmapSourceToByteBase64(System.Windows.Media.Imaging.
{
    var encoder = new System.Windows.Media.Imaging.JpegBitmapEncoder();
    var frame = System.Windows.Media.Imaging.BitmapFrame.Create(source);
    encoder.Frames.Add(frame);
    var stream = new MemoryStream();

    encoder.Save(stream);
    return Convert.ToBase64String(stream.ToArray());
    //I tired to do return "data:image/name_jpg;base64,"+Convert.ToBase64String(stream.ToArray());
    //But got an exception on serialize base64 div 4 in the web client
}

在我的网站上，我获取了数据(base64 图像)并尝试执行以下操作: context.drawImage(0,0,'data:image/jpeg;base64,'+image); 我也试过: context.drawImage('data:image/jpeg;base64,'+image,0,0);

不工作!!!有什么想法吗？

Answer 1

您无需“解码”base64 字符串即可在 Canvas 中绘制它，只需将其分配给图像源并在 Canvas 中绘制该图像即可。

像这样:

var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
var img = new Image();

img.onload = function() {
  context.drawImage(this, 0, 0, canvas.width, canvas.height);
}

img.src = "data:image/gif;base64,R0lGODlhDwAPAKECAAAAzMzM/////wAAACwAAAAADwAPAAACIISPeQHsrZ5ModrLlN48CXF8m2iQ3YmmKqVlRtW4MLwWACH+H09wdGltaXplZCBieSBVbGVhZCBTbWFydFNhdmVyIQAAOw==";

<canvas id="canvas" width="50" height="50"></canvas>

确保您的 base64 字符串以 data:image/gif;base64, 部分开头。

image/jpeg、image/png 等。取决于您的编码图像格式。