Question

当我将图像添加到画布（drawImage）时，类型的问题，当我用其他画布方法绘制绘图时，我没有任何问题。

var ready;
ready = function() {
var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');
var imageObj = new Image();

imageObj.src = 'http://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';

imageObj.onload = function() {
  context.drawImage(imageObj, 69, 50);
};

var pngUrl = canvas.toDataURL();
console.log(pngUrl);
$('#client_avatar').val(pngUrl);

};

Answer 1

在设置源码之前，你必须定义onload否则它将无法调用onload。

$(document).ready(function() {
    var canvas = document.getElementById('canvas');
    var context = canvas.getContext('2d');
    var imageObj = new Image();


    imageObj.onload = function() {
      context.drawImage(imageObj, 69, 50);
    };
    imageObj.src = 'http://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';


    var pngUrl = canvas.toDataURL();
    console.log(pngUrl);
//    $('#client_avatar').val(pngUrl);
$("#client_avatar").append("<img src='"+ pngUrl +"'>")

    });

这是工作jsbin link

Answer 2

$(document).ready(function() {
   var canvas = document.getElementById('canvas');
   var context = canvas.getContext('2d');
   var imageObj = new Image();

   imageObj.onload = function() {
      context.drawImage(imageObj, 0, 0, 200, 200);
      var pngUrl = canvas.toDataURL();
      console.log(pngUrl);
      $('#client_avatar').attr('src', pngUrl);
   };

   imageObj.crossOrigin = 'anonymous'; //not necessary, if image hosted on same server
   imageObj.src = 'https://i.imgur.com/Q6aZlme.jpg';
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<canvas id="canvas" width="200" height="200"></canvas>
<img id="client_avatar">

^{没有给出任何解释的道歉}

ʜᴀᴠᴇꜰᴜɴ：）

canvas + drawImage，toDataURL返回空白图像

2 个答案: