Firefox 不会在第一次访问时绘制到 canvas

Question

我有一个问题，我很难相信...当我在 Firefox 中绘制动态创建的 canvas 时，它似乎不会在源为 [=41= 的第一时间呈现]... 这似乎是第一次发生 JavaScript 问题是运行通过修改源代码或第一次访问 link。以下是一些重现步骤：

1) 打开一个全新的 Firefox 实例。访问下面的 jsFiddle。

2) 什么也没看到

3) 在 Firefox 中打开一个新选项卡。访问下面的 jsFiddle。

4) 查看结果（10 个彩色方块）

在 Chrome 中执行此操作将导致在第 2 步和第 4 步中看到结果。

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));
    }

});

Answer 1

您应该等待 load event 在图像上触发，然后再将其绘制到 canvas。即使图像数据作为数据 URI 嵌入，也不能保证在您设置 src 时图像会被渲染并准备好绘制。等待 load 事件将确保图像准备就绪。

工作示例（JSFiddle）：

$(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>

Firefox 不会在第一次访问时绘制到 canvas

Firefox won't draw to canvas on first visit

html

javascript

firefox

canvas

drawimage

工作示例（JSFiddle）：