应用场景
生成带二维码的推广海报图片
旧方法:
将用户自己的推广连接先通过qrcode.js生成二维码，然后再用后台返回的一张背景图片和二维码通过canvas绘制成一张海报。
问题
在部分安卓手机上获取二维码图片后，onload事件不起作用，代码演示如下。
<!---放二维码--->
<div id="imgs" style="100px; height:100px; margin-top:15px;"hidden></div>
<!-- 生成canvas海报 -->
<canvas id="myCanvas" width="" height=""></canvas>
<!-- 生成canvas海报 -->
<!--海报弹窗-->
<div class="shadow" onclick="shareHide()"></div>
<img class="shareImg" id="imgShow" src="">
<script type="text/javascript">
document.onreadystatechange = loadingChange; // 当页面加载状态改变的时候执行这个方法.
function loadingChange()
{
if(document.readyState == "Loading") { // 当页面加载状态为完全结束时进入
// $(".shodowS").show()
}
if(document.readyState == "complete") { // 当页面加载状态为完全结束时进入
var qrcodes = new QRCode(document.getElementById("imgs"), {
width : 160,
height : 160
});
qrcodes.makeCode('{$url}'); // 生成二维码
shareImgs();
}
}
var canvas = document.getElementById('myCanvas');
canvas.width=$("#container").width()*2;
canvas.height=$("#container").width()*1440/1080*2;
$("#myCanvas").css("width",$("#container").width());
$("#myCanvas").css("height",$("#container").width()*1440/1080);
// 分享图片生成的
function shareImgs() {
var qrcode=document.getElementById("imgss");
if (canvas.getContext) {
var ctx = canvas.getContext('2d');
//创建新的图片对象
var img = document.getElementById("imgs1");
var img = new Image;
//指定图片的URL
// img.crossOrigin="anonymous"; // 这个可以对苹果手机做兼容(跨域)
// img.src=img.src;
img.src='{$bg[0]}';
img.onload = function() {
var imgOw=img.width,imgOh=img.height;
var imgW=canvas.width,imgH=(imgOh*canvas.width)/imgOw;
var imgX=0,imgY=0;
//以Canvas画布上的坐标(10,10)为起始点，绘制图像
ctx.drawImage(img, imgX, imgY,imgW,imgH);
var qrcodeX, qrcodeY,qrcodeW,qrcodeH;
qrcode.crossOrigin="anonymous";
qrcode.src=qrcode.src;
qrcode.onload = function() {
//以Canvas画布上的坐标(10,10)为起始点，绘制图像
ctx.drawImage(qrcode,846/1080*canvas.width, 1220/1440*(imgOh*canvas.width)/imgOw+(canvas.height-imgH)/2, 160/1440*img.width, 160/1440*img.width);
var _imgSrc = canvas.toDataURL("image/png",1);
var imgShow = document.getElementById('imgShow');
imgShow.setAttribute('src', _imgSrc);
}
}
}
}
</script> 
解决方法
虽然知道是页面渲染的先后问题，但是时间很紧，只能跳过使用另一种方式解决这种在有的手机上不能生成海报的问题。所以决定通过后台生成二维码放在页面，然后JS只需要获取后台返回的base64二维码和海报绘制再生成图片，最后安卓苹果手机都能显示了。
1. 使用的是phpqrcode类，不过需要简单的修改一下，让其能生成base64的二维码，这个我是在网上参考别人的源码，具体是谁忘记了，记起后代码原著我会补上，这里就代码先上了。
<?php
/*
* Version: 1.1.4
* Build: 2010100721
*/
//---- qrconst.php -----------------------------
/*
* PHP QR Code encoder
*
* Common constants
*
* Based on libqrencode C library distributed under LGPL 2.1
* Copyright (C) 2006, 2007, 2008, 2009 Kentaro Fukuchi <fukuchi@megaui.net>
*
* PHP QR Code is distributed under LGPL 3
* Copyright (C) 2010 Dominik Dzienia <deltalab at poczta dot fm>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3 of the License, or any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
// Encoding modes
define('QR_MODE_NUL', -1);
define('QR_MODE_NUM', 0);
define('QR_MODE_AN', 1);
define('QR_MODE_8', 2);
define('QR_MODE_KANJI', 3);
define('QR_MODE_STRUCTURE', 4);
// Levels of error correction.
define('QR_ECLEVEL_L', 0);
define('QR_ECLEVEL_M', 1);
define('QR_ECLEVEL_Q', 2);
define('QR_ECLEVEL_H', 3);
// Supported output formats
define('QR_FORMAT_TEXT', 0);
define('QR_FORMAT_PNG', 1);
class qrstr {
public static function set(&$srctab, $x, $y, $repl, $replLen = false) {
$srctab[$y] = substr_replace($srctab[$y], ($replLen !== false)?substr($repl,0,$replLen):$repl, $x, ($replLen !== false)?$replLen:strlen($repl));
}
}
//---- merged_config.php -----------------------------
/*
* PHP QR Code encoder
*
* Config file, tuned-up for merged verion
*/
define('QR_CACHEABLE', false); // use cache - more disk reads but less CPU power, masks and format templates are stored there
define('QR_CACHE_DIR', false); // used when QR_CACHEABLE === true
define('QR_LOG_DIR', false); // default error logs dir
define('QR_FIND_BEST_MASK', true); // if true, estimates best mask (spec. default, but extremally slow; set to false to significant performance boost but (propably) worst quality code
define('QR_FIND_FROM_RANDOM', 2); // if false, checks all masks available, otherwise value tells count of masks need to be checked, mask id are got randomly
define('QR_DEFAULT_MASK', 2); // when QR_FIND_BEST_MASK === false
define('QR_PNG_MAXIMUM_SIZE', 1024); // maximum allowed png image width (in pixels), tune to make sure GD and PHP can handle such big images
//---- qrtools.php -----------------------------
/*
* PHP QR Code encoder
*
* Toolset, handy and debug utilites.
*
* PHP QR Code is distributed under LGPL 3
* Copyright (C) 2010 Dominik Dzienia <deltalab at poczta dot fm>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3 of the License, or any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
class QRtools {
//----------------------------------------------------------------------
public static function binarize($frame)
{
$len = count($frame);
foreach ($frame as &$frameLine) {
for($i=0; $i<$len; $i++) {
$frameLine[$i] = (ord($frameLine[$i])&1)?'1':'0';
}
}
return $frame;
}
//----------------------------------------------------------------------
public static function tcpdfBarcodeArray($code, $mode = 'QR,L', $tcPdfVersion = '4.5.037')
{
$barcode_array = array();
if (!is_array($mode))
$mode = explode(',', $mode);
$eccLevel = 'L';
if (count($mode) > 1) {
$eccLevel = $mode[1];
}
$qrTab = QRcode::text($code, false, $eccLevel);
$size = count($qrTab);
$barcode_array['num_rows'] = $size;
$barcode_array['num_cols'] = $size;
$barcode_array['bcode'] = array();
foreach ($qrTab as $line) {
$arrAdd = array();
foreach(str_split($line) as $char)
$arrAdd[] = ($char=='1')?1:0;
$barcode_array['bcode'][] = $arrAdd;
}
return $barcode_array;
}
//----------------------------------------------------------------------
public static function clearCache()
{
self::$frames = array();
}
//----------------------------------------------------------------------
public static function buildCache()
{
QRtools::markTime('before_build_cache');
$mask = new QRmask();
for ($a=1; $a <= QRSPEC_VERSION_MAX; $a++) {
$frame = QRspec::newFrame($a);
if (QR_IMAGE) {
$fileName = QR_CACHE_DIR.'frame_'.$a.'.png';
QRimage::png(self::binarize($frame), $fileName, 1, 0);
}
$width = count($frame);
$bitMask = array_fill(0, $width, array_fill(0, $width, 0));
for ($maskNo=0; $maskNo<8; $maskNo++)
$mask->makeMaskNo($maskNo, $width, $frame, $bitMask, true);
}
QRtools::markTime('after_build_cache');
}
//----------------------------------------------------------------------
public static function log($outfile, $err)
{
if (QR_LOG_DIR !== false) {
if ($err != '') {
if ($outfile !== false) {
file_put_contents(QR_LOG_DIR.basename($outfile).'-errors.txt', date('Y-m-d H:i:s').': '.$err, FILE_APPEND);
} else {
file_put_contents(QR_LOG_DIR.'errors.txt', date('Y-m-d H:i:s').': '.$err, FILE_APPEND);
}
}
}
}
//----------------------------------------------------------------------
public static function dumpMask($frame)
{
$width = count($frame);
for($y=0;$y<$width;$y++) {
for($x=0;$x<$width;$x++) {
echo ord($frame[$y][$x]).',';
}
}
}
//----------------------------------------------------------------------
public static function markTime($markerId)
{
list($usec, $sec) = explode(" ", microtime());
$time = ((float)$usec + (float)$sec);
if (!isset($GLOBALS['qr_time_bench']))
$GLOBALS['qr_time_bench'] = array();
$GLOBALS['qr_time_bench'][$markerId] = $time;
}
//----------------------------------------------------------------------
public static function timeBenchmark()
{
self::markTime('finish');
$lastTime = 0;
$startTime = 0;
$p = 0;
echo '<table cellpadding="3" cellspacing="1">
<thead><tr style="border-bottom:1px solid silver"><td colspan="2" style="text-align:center">BENCHMARK</td></tr></thead>
<tbody>';
foreach($GLOBALS['qr_time_bench'] as $markerId=>$thisTime) {
if ($p > 0) {
echo '<tr><th style="text-align:right">till '.$markerId.': </th><td>'.number_format($thisTime-$lastTime, 6).'s</td></tr>';
} else {
$startTime = $thisTime;
}
$p++;
$lastTime = $thisTime;
}
echo '</tbody><tfoot>
<tr style="border-top:2px solid black"><th style="text-align:right">TOTAL: </th><td>'.number_format($lastTime-$startTime, 6).'s</td></tr>
</tfoot>
</table>';
}
}
//##########################################################################
QRtools::markTime('start');
//---- qrspec.php -----------------------------
/*
* PHP QR Code encoder
*
* QR Code specifications
*
* Based on libqrencode C library distributed under LGPL 2.1
* Copyright (C) 2006, 2007, 2008, 2009 Kentaro Fukuchi <fukuchi@megaui.net>
*
* PHP QR Code is distributed under LGPL 3
* Copyright (C) 2010 Dominik Dzienia <deltalab at poczta dot fm>
*
* The following data / specifications are taken from
* "Two dimensional symbol -- QR-code -- Basic Specification" (JIS X0510:2004)
* or
* "Automatic identification and data capture techniques --
* QR Code 2005 bar code symbology specification" (ISO/IEC 18004:2006)
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3 of the License, or any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
define('QRSPEC_VERSION_MAX', 40);
define('QRSPEC_WIDTH_MAX', 177);
define('QRCAP_WIDTH', 0);
define('QRCAP_WORDS', 1);
define('QRCAP_REMINDER',