スマホが登場してから、WEB画面の構造が複雑になってきたりしています。
パソコン、ガラケー
の2つの切替でよかったのが
スマホ
という画面サイズが異なるデバイスが登場してから、「アクセスしてくるデバイスによって切り替える画面」てのが増えて来ました。
現在では、アクセス数をみると スマホ > パソコン > ガラケー ということになってきているので、WEBサイトのスマホに向けての最適化は避けて通ることができません。
このスマホが厄介で、画面レイアウトやフォントのHTMLやCSS部分はそれなりにスマホブラウザが見やすく表示してくれるのですが、画像についてはうまくサイズ調節はしてくれなかったりします。
スマホは、画面サイズは端末によって違うので、HTMLをいくらレスポンシブにしたとしても、スマホ画面に合わせての「画像の切替」などという処理が必要になってきます。
切替 ということは、いくつかの画像サイズを実際に作成することになるのですが、面倒なので、WEBサイトへのアクセス時にサーバ側で画像を書き出しすることにします。
画像の処理というのは、サーバの負荷を上げますので、キャッシュの機能は必須だと思われます。
ということで、「Adaptive Images」というPHPライブラリを使ってやってみます。ライブラリといってもPHPスクリプトはひとつです。
作業は以下の手順となります。
1. .htaccess(mod_rewite) により、画像ファイルへのアクセスをPHPスクリプトに向ける。
2. PHPライブラリ adaptive-images.php をサーバに配置。
3. JavaScriptをHTMLヘッダー内に挿入する。
これだけです。
今すぐコンソールを開いて、コピペでやってみましょう。
.htaccess (DocumentRoot直下)
<IfModule mod_rewrite.c>
Options +FollowSymlinks
RewriteEngine On
# Adaptive-Images -----------------------------------------------------------------------------------
# Add any directories you wish to omit from the Adaptive-Images process on a new line, as follows:
# RewriteCond %{REQUEST_URI} !ignore-this-directory
# RewriteCond %{REQUEST_URI} !and-ignore-this-directory-too
RewriteCond %{REQUEST_URI} !assets
# don't apply the AI behaviour to images inside AI's cache folder:
RewriteCond %{REQUEST_URI} !ai-cache
# Send any GIF, JPG, or PNG request that IS NOT stored inside one of the above directories
# to adaptive-images.php so we can select appropriately sized versions
RewriteRule \.(?:jpe?g|gif|png)$ adaptive-images.php
# END Adaptive-Images -------------------------------------------------------------------------------
</IfModule>
adaptive-images.php (DocumentRoot直下)
/* PROJECT INFO --------------------------------------------------------------------------------------------------------
Version: 1.5.2
Changelog: http://adaptive-images.com/changelog.txt
Homepage: http://adaptive-images.com
GitHub: https://github.com/MattWilcox/Adaptive-Images
Twitter: @responsiveimg
LEGAL:
Adaptive Images by Matt Wilcox is licensed under a Creative Commons Attribution 3.0 Unported License.
/* CONFIG ----------------------------------------------------------------------------------------------------------- */
$resolutions = array(1382, 992, 768, 480); // the resolution break-points to use (screen widths, in pixels)
$cache_path = "ai-cache"; // where to store the generated re-sized images. Specify from your document root!
$jpg_quality = 75; // the quality of any generated JPGs on a scale of 0 to 100
$sharpen = TRUE; // Shrinking images can blur details, perform a sharpen on re-scaled images?
$watch_cache = TRUE; // check that the adapted image isn't stale (ensures updated source images are re-cached)
$browser_cache = 60*60*24*7; // How long the BROWSER cache should last (seconds, minutes, hours, days. 7days by default)
/* END CONFIG ----------------------------------------------------------------------------------------------------------
------------------------ Don't edit anything after this line unless you know what you're doing -------------------------
--------------------------------------------------------------------------------------------------------------------- */
/* get all of the required data from the HTTP request */
$document_root = $_SERVER['DOCUMENT_ROOT'];
$requested_uri = parse_url(urldecode($_SERVER['REQUEST_URI']), PHP_URL_PATH);
$requested_file = basename($requested_uri);
$source_file = $document_root.$requested_uri;
$resolution = FALSE;
/* Mobile detection
NOTE: only used in the event a cookie isn't available. */
function is_mobile() {
$userAgent = strtolower($_SERVER['HTTP_USER_AGENT']);
return strpos($userAgent, 'mobile');
}
/* Does the UA string indicate this is a mobile? */
if(!is_mobile()){
$is_mobile = FALSE;
} else {
$is_mobile = TRUE;
}
// does the $cache_path directory exist already?
if (!is_dir("$document_root/$cache_path")) { // no
if (!mkdir("$document_root/$cache_path", 0755, true)) { // so make it
if (!is_dir("$document_root/$cache_path")) { // check again to protect against race conditions
// uh-oh, failed to make that directory
sendErrorImage("Failed to create cache directory at: $document_root/$cache_path");
}
}
}
/* helper function: Send headers and returns an image. */
function sendImage($filename, $browser_cache) {
$extension = strtolower(pathinfo($filename, PATHINFO_EXTENSION));
if (in_array($extension, array('png', 'gif', 'jpeg'))) {
header("Content-Type: image/".$extension);
} else {
header("Content-Type: image/jpeg");
}
header("Cache-Control: private, max-age=".$browser_cache);
header('Expires: '.gmdate('D, d M Y H:i:s', time()+$browser_cache).' GMT');
header('Content-Length: '.filesize($filename));
readfile($filename);
exit();
}
/* helper function: Create and send an image with an error message. */
function sendErrorImage($message) {
/* get all of the required data from the HTTP request */
$document_root = $_SERVER['DOCUMENT_ROOT'];
$requested_uri = parse_url(urldecode($_SERVER['REQUEST_URI']), PHP_URL_PATH);
$requested_file = basename($requested_uri);
$source_file = $document_root.$requested_uri;
if(!is_mobile()){
$is_mobile = "FALSE";
} else {
$is_mobile = "TRUE";
}
$im = ImageCreateTrueColor(800, 300);
$text_color = ImageColorAllocate($im, 233, 14, 91);
$message_color = ImageColorAllocate($im, 91, 112, 233);
ImageString($im, 5, 5, 5, "Adaptive Images encountered a problem:", $text_color);
ImageString($im, 3, 5, 25, $message, $message_color);
ImageString($im, 5, 5, 85, "Potentially useful information:", $text_color);
ImageString($im, 3, 5, 105, "DOCUMENT ROOT IS: $document_root", $text_color);
ImageString($im, 3, 5, 125, "REQUESTED URI WAS: $requested_uri", $text_color);
ImageString($im, 3, 5, 145, "REQUESTED FILE WAS: $requested_file", $text_color);
ImageString($im, 3, 5, 165, "SOURCE FILE IS: $source_file", $text_color);
ImageString($im, 3, 5, 185, "DEVICE IS MOBILE? $is_mobile", $text_color);
header("Cache-Control: no-store");
header('Expires: '.gmdate('D, d M Y H:i:s', time()-1000).' GMT');
header('Content-Type: image/jpeg');
ImageJpeg($im);
ImageDestroy($im);
exit();
}
/* sharpen images function */
function findSharp($intOrig, $intFinal) {
$intFinal = $intFinal * (750.0 / $intOrig);
$intA = 52;
$intB = -0.27810650887573124;
$intC = .00047337278106508946;
$intRes = $intA + $intB * $intFinal + $intC * $intFinal * $intFinal;
return max(round($intRes), 0);
}
/* refreshes the cached image if it's outdated */
function refreshCache($source_file, $cache_file, $resolution) {
if (file_exists($cache_file)) {
// not modified
if (filemtime($cache_file) >= filemtime($source_file)) {
return $cache_file;
}
// modified, clear it
unlink($cache_file);
}
return generateImage($source_file, $cache_file, $resolution);
}
/* generates the given cache file for the given source file with the given resolution */
function generateImage($source_file, $cache_file, $resolution) {
global $sharpen, $jpg_quality;
$extension = strtolower(pathinfo($source_file, PATHINFO_EXTENSION));
// Check the image dimensions
$dimensions = GetImageSize($source_file);
$width = $dimensions[0];
$height = $dimensions[1];
// Do we need to downscale the image?
if ($width <= $resolution) { // no, because the width of the source image is already less than the client width
return $source_file;
}
// We need to resize the source image to the width of the resolution breakpoint we're working with
$ratio = $height/$width;
$new_width = $resolution;
$new_height = ceil($new_width * $ratio);
$dst = ImageCreateTrueColor($new_width, $new_height); // re-sized image
switch ($extension) {
case 'png':
$src = @ImageCreateFromPng($source_file); // original image
break;
case 'gif':
$src = @ImageCreateFromGif($source_file); // original image
break;
default:
$src = @ImageCreateFromJpeg($source_file); // original image
ImageInterlace($dst, true); // Enable interlancing (progressive JPG, smaller size file)
break;
}
if($extension=='png'){
imagealphablending($dst, false);
imagesavealpha($dst,true);
$transparent = imagecolorallocatealpha($dst, 255, 255, 255, 127);
imagefilledrectangle($dst, 0, 0, $new_width, $new_height, $transparent);
}
ImageCopyResampled($dst, $src, 0, 0, 0, 0, $new_width, $new_height, $width, $height); // do the resize in memory
ImageDestroy($src);
// sharpen the image?
// NOTE: requires PHP compiled with the bundled version of GD (see http://php.net/manual/en/function.imageconvolution.php)
if($sharpen == TRUE && function_exists('imageconvolution')) {
$intSharpness = findSharp($width, $new_width);
$arrMatrix = array(
array(-1, -2, -1),
array(-2, $intSharpness + 12, -2),
array(-1, -2, -1)
);
imageconvolution($dst, $arrMatrix, $intSharpness, 0);
}
$cache_dir = dirname($cache_file);
// does the directory exist already?
if (!is_dir($cache_dir)) {
if (!mkdir($cache_dir, 0755, true)) {
// check again if it really doesn't exist to protect against race conditions
if (!is_dir($cache_dir)) {
// uh-oh, failed to make that directory
ImageDestroy($dst);
sendErrorImage("Failed to create cache directory: $cache_dir");
}
}
}
if (!is_writable($cache_dir)) {
sendErrorImage("The cache directory is not writable: $cache_dir");
}
// save the new file in the appropriate path, and send a version to the browser
switch ($extension) {
case 'png':
$gotSaved = ImagePng($dst, $cache_file);
break;
case 'gif':
$gotSaved = ImageGif($dst, $cache_file);
break;
default:
$gotSaved = ImageJpeg($dst, $cache_file, $jpg_quality);
break;
}
ImageDestroy($dst);
if (!$gotSaved && !file_exists($cache_file)) {
sendErrorImage("Failed to create image: $cache_file");
}
return $cache_file;
}
// check if the file exists at all
if (!file_exists($source_file)) {
header("Status: 404 Not Found");
exit();
}
/* check that PHP has the GD library available to use for image re-sizing */
if (!extension_loaded('gd')) { // it's not loaded
if (!function_exists('dl') || !dl('gd.so')) { // and we can't load it either
// no GD available, so deliver the image straight up
trigger_error('You must enable the GD extension to make use of Adaptive Images', E_USER_WARNING);
sendImage($source_file, $browser_cache);
}
}
/* Check to see if a valid cookie exists */
if (isset($_COOKIE['resolution'])) {
$cookie_value = $_COOKIE['resolution'];
// does the cookie look valid? [whole number, comma, potential floating number]
if (! preg_match("/^[0-9]+[,]*[0-9\.]+$/", "$cookie_value")) { // no it doesn't look valid
setcookie("resolution", "$cookie_value", time()-100); // delete the mangled cookie
}
else { // the cookie is valid, do stuff with it
$cookie_data = explode(",", $_COOKIE['resolution']);
$client_width = (int) $cookie_data[0]; // the base resolution (CSS pixels)
$total_width = $client_width;
$pixel_density = 1; // set a default, used for non-retina style JS snippet
if (@$cookie_data[1]) { // the device's pixel density factor (physical pixels per CSS pixel)
$pixel_density = $cookie_data[1];
}
rsort($resolutions); // make sure the supplied break-points are in reverse size order
$resolution = $resolutions[0]; // by default use the largest supported break-point
// if pixel density is not 1, then we need to be smart about adapting and fitting into the defined breakpoints
if($pixel_density != 1) {
$total_width = $client_width * $pixel_density; // required physical pixel width of the image
// the required image width is bigger than any existing value in $resolutions
if($total_width > $resolutions[0]){
// firstly, fit the CSS size into a break point ignoring the multiplier
foreach ($resolutions as $break_point) { // filter down
if ($total_width <= $break_point) {
$resolution = $break_point;
}
}
// now apply the multiplier
$resolution = $resolution * $pixel_density;
}
// the required image fits into the existing breakpoints in $resolutions
else {
foreach ($resolutions as $break_point) { // filter down
if ($total_width <= $break_point) {
$resolution = $break_point;
}
}
}
}
else { // pixel density is 1, just fit it into one of the breakpoints
foreach ($resolutions as $break_point) { // filter down
if ($total_width <= $break_point) {
$resolution = $break_point;
}
}
}
}
}
/* No resolution was found (no cookie or invalid cookie) */
if (!$resolution) {
// We send the lowest resolution for mobile-first approach, and highest otherwise
$resolution = $is_mobile ? min($resolutions) : max($resolutions);
}
/* if the requested URL starts with a slash, remove the slash */
if(substr($requested_uri, 0,1) == "/") {
$requested_uri = substr($requested_uri, 1);
}
/* whew might the cache file be? */
$cache_file = $document_root."/$cache_path/$resolution/".$requested_uri;
/* Use the resolution value as a path variable and check to see if an image of the same name exists at that path */
if (file_exists($cache_file)) { // it exists cached at that size
if ($watch_cache) { // if cache watching is enabled, compare cache and source modified dates to ensure the cache isn't stale
$cache_file = refreshCache($source_file, $cache_file, $resolution);
}
sendImage($cache_file, $browser_cache);
}
/* It exists as a source file, and it doesn't exist cached - lets make one: */
$file = generateImage($source_file, $cache_file, $resolution);
sendImage($file, $browser_cache);
HTMLヘッダ内に挿入するJavaScript
<script>document.cookie='resolution='+Math.max(screen.width,screen.height)+'; path=/';</script>
あとキャッシュを使うのは、ドキュメントルート直下に、ディレクトリ「ai-cache」を作るとか、シンプルな構造なのでいろんなことができると思われます。
関連ワード: Android・WEB・おすすめ・便利な設定・開発・Adaptive Images・レスポンシブ・画像問題