在Javascript中将Base64数据转换并插入Canvas

Question

我得到一个数据缓冲区代表Base64中的图像。 我得到的数据（代表base64中的图像）（部分数据）

193,109,51,74,182,71,212,38,78,62,211,48,81,145,244,39,244,250,215,192,113,46,101,136,203,149,44,6,90,147,197,215,109,66,251,69,47,138,111,202,43,239,122,45,108,125,22,6,149,44,84,103,136,198,74,212,41,171,203,188,187,69,121,183,255,0,7,75,156,191,140,190,45,181,219,141,43,195,214,107,30,129,3,145,38,110,60,135,185,35,130,119,4,108,244,238,0,227,3,140,86,85,237,134,149,241,3,69,158,251,71,134,93,31,88,211,72,82,1,30,100,76,70,65,12,9,12,141,207,94,184,32,140,215,45,47,196,111,130,177,187,34,120,79,197,65,84,224,8,175,93,20,99,176,31,107,24,250,96,85,141,47,227,159,195,111,11,219,223,46,133,225,175,17,91,73,120,170,178,189,196,137,49,96,185,218,50,247,44,64,27,155,167,173,123,252,61,144,97,242,8,63,102,156,234,207,227,169,43,115,77,245,230,119,122,111,104,173,23,78,167,204,103,121,165,108,217,46,88,184,40,124.....

成功解码。

现在我正在尝试将图像添加到我的画布而没有成功，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);
            //}
        }
    }
}

我将数据格式转换为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，我得到了数据（base64图像）并尝试执行以下操作：context.drawImage（0,0，'data：image / jpeg; base64，'+ image）; 我也尝试过：context.drawImage（'data：image / jpeg; base64，'+ image，0,0）;

不行！！！ 任何的想法？

Answer 1

您不需要“解码”base64字符串以在画布中绘制它，只需将其分配给图像源并在画布中绘制该图像。

像这样的东西：

 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> 

确保你的base64字符串以data:image/gif;base64, part开头。

image/jpeg ， image/png等。取决于您编码的图像格式。

Answer 2

http：// localhost：994 /％FF％ ......无法在画布上绘制。
您的数据应该看起来像“data：image / png; base64，iVBORw0 ......”
如果它们看起来像这样，那么它们就可以在没有base64解码的情况下使用。 您只需使用context.drawImage直接绘制它们