Firefox不会在初次访问时就绘制画布 [英] Firefox won't draw to canvas on first visit
问题描述
我遇到了一个难以置信的问题...似乎当我在Firefox中绘制到动态创建的画布时，它并不会在第一次运行源代码时就渲染它...似乎是在第一次通过修改源代码或第一次访问链接来运行有问题的JavaScript。以下是一些复制步骤：
I have an issue I'm having a hard time believing... It seems that when I draw to a dynamically created canvas in Firefox it wont render the first time that source is run... It seems to happen the first time the JavaScript in question is run either by modifying the source or visiting the link for the first time. Here are some repro steps:
1）打开一个全新的Firefox实例。
1) open a brand new instance of Firefox. visit the jsFiddle below.
2）什么都看不见
3）在Firefox中打开一个新标签页。请访问下面的jsFiddle。
3) open a new tab in Firefox. visit the jsFiddle below.
4）查看结果（10个彩色正方形）
4) see the result (10 colored squares)
在Chrome中执行此操作将导致在步骤2和步骤4都看到结果。
Doing this in Chrome will result in seeing the result at both step 2 and step 4.
https://jsfiddle.net/sk873txv/1/
html
<body>
<div id="a">
</div>
</body>
js
$(document).ready(function(){
var make_canvas = function(i) {
var $canvas = $('<canvas>').appendTo($('#a'));
$canvas.attr('width', '100px');
$canvas.attr('height', '100px');
var canvas = $canvas[0];
var ctx = canvas.getContext('2d');
return ctx;
};
var draw = function(ctx) {
var image = new Image();
image.src = "data:image/png;base64,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";
ctx.drawImage(image, 0, 0);
};
for(var i = 0; i < 10; i++)
{
draw(make_canvas(i));
}
});
推荐答案
您应该等待 load 事件触发图像，然后再将其绘制到画布上。即使将图像数据作为数据URI嵌入，也不能保证在设置 src 的瞬间即可绘制图像并准备好绘制。等待 load 事件将确保图像准备就绪。
You should wait for the load event to fire on the image, before drawing it to a canvas. Even though the image data is embedded as a data URI, there is no guarantee the image will be rendered and ready to draw the instant you set the src. Waiting for the load event will ensure the image is ready.
$(document).ready(function(){
var make_canvas = function(i) {
var $canvas = $('<canvas>').appendTo($('#a'));
$canvas.attr('width', '100px');
$canvas.attr('height', '100px');
var canvas = $canvas[0];
var ctx = canvas.getContext('2d');
return ctx;
};
var draw = function(ctx) {
var image = new Image();
image.onload = function() {
ctx.drawImage(image, 0, 0);
};
image.src = "data:image/png;base64,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";
};
for(var i = 0; i < 10; i++)
{
draw(make_canvas(i));
}
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<body>
<div id="a">
</div>
</body>
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