HTML5畫布toDataURL返回空白圖像

Question

用一張空白的畫布開始：

<canvas id='myCanvas' width='800' height='600'></canvas> 

然後初始化是帆布：

function init_canvas(){ 
    var canvas = document.getElementById('myCanvas'); 
    context = canvas.getContext('2d'); 
    context.lineCap = 'round'; 
    // fill it with white background 
    context.save(); 
    context.fillStyle = '#fff'; 
    context.fillRect(0, 0, context.canvas.width, context.canvas.height); 
    context.restore(); 
    return; 
    } 

然後做了一堆畫布上繪畫。

然後嘗試在後端使用ajax和PHP將其保存到服務器。

在客戶端：

var img = canvas.toDataURL('image/png'); 
// strip the leading garbage. 
img.substr(img.indexOf(',')+1).toString(); 

拿得到的字符串，這是base64編碼的PNG，直接把PHP和和BASE64_DECODE（）字符串...圖像始終是正確的大小，但它有沒有繪製它 - 只是一個透明的圖像。這在PHP中似乎不是base64_decode（）的問題，它似乎是一個安全問題或其他問題。它在Firefox 4和最新的Chrome中均失敗。

所產生的PNG圖像轉儲到火狐「圖像/ PNG」頭產生這個錯誤控制檯：

Error: Image corrupt or truncated: http://somewhere.com/showimage.php 
Source file: http://somewhere.com/showimage.php 

但是...圖像不損壞或截斷，我可以看出，除非toDataURL （）隨處可見，因爲php的東西只是base64_decode（）toDataURL（）的結果。

任何想法？

謝謝！

Answer 1

檢查你見過在PHP文檔的base64_decodethis comment？

如果要保存從Javascript canvas.toDataURL（）函數派生的數據，則必須將空白轉換爲加號。 如果你不這樣做，解碼後的數據被破壞：

<?php 
    $encodedData = str_replace(' ','+',$encodedData); 
    $decocedData = base64_decode($encodedData); 
?> 

Answer 2

是否像我之前的問題？

可能是你可以在

jQuery and Canvas.toDataURL

和

Security error" code: "1000 on Firefox with Canvas.toDataURL

Answer 3

在JavaScript從canvas.toDataURL()這些瀏覽器比支持此方法與「圖像/ PNG」的默認類型發送的結果。

var imageInfo = canvas.toDataURL(); 

直接的方式來創建PNG文件：

<?php 
$imageInfo = imageInfoFromBrowser(); // Your method to get the data 
$image = fopen($imageInfo, 'r'); 
file_put_contents("fileName.png", $image); 
fclose($image); 
?> 

我在PHP 5.3這個工作，對於其他版本，請檢查。

用於在PHP上進行測試的圖像數據樣本。

$imageDataInfoSample = "data:image/png;base64,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"