// put this above any php image generation code: session_start(); header("Cache-Control: private, max-age=10800, pre-check=10800"); header("Pragma: private"); header("Expires: " . date(DATE_RFC822,strtotime(" 2 day")));
情况一:如果浏览器对当前页面已经有缓存,那么就直接使用它。
// the browser will send a $_SERVER['HTTP_IF_MODIFIED_SINCE'] if it has a cached copy if(isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])){ // if the browser has a cached version of this image, send 304 header('Last-Modified: '.$_SERVER['HTTP_IF_MODIFIED_SINCE'],true,304); exit; }
$img = "some_image.png"; if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && (strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) == filemtime($img))) { // send the last mod time of the file back header('Last-Modified: '.gmdate('D, d M Y H:i:s', filemtime($img)).' GMT',true, 304); exit; }
<?php //调整图片大小 /** *图片按比例调整大小的原理: *1、比较原图大小是否小于等于目标大小,如果是则直接采用原图宽高 *2、如果原图大小超过目标大小,则对比原图宽高大小 *3、如:宽>高,则宽=目标宽, 高=目标宽的比例 * 原高 *4、如:高>宽,则高=目标高,宽=目标高的比例 * 原宽 **/ $image = "test.jpg"; $max_width = 200; $max_height = 200; $size = getimagesize($image); //得到图像的大小 $width = $size[0]; $height = $size[1]; $x_ratio = $max_width / $width; $y_ratio = $max_height / $height; if (($width <= $max_width) && ($height <= $max_height)) { $tn_width = $width; $tn_height = $height; } elseif (($x_ratio * $height) < $max_height) { $tn_height = ceil($x_ratio * $height); $tn_width = $max_width; } else { $tn_width = ceil($y_ratio * $width); $tn_height = $max_height; } $src = imagecreatefromjpeg($image); $dst = imagecreatetruecolor($tn_width, $tn_height); //新建一个真彩色图像 imagecopyresampled($dst, $src, 0, 0, 0, 0,$tn_width, $tn_height, $width, $height); //重采样拷贝部分图像并调整大小 header('Content-Type: image/jpeg'); imagejpeg($dst,null,100); imagedestroy($src); imagedestroy($dst); ?>
希望本文所述对大家的PHP程序设计有所帮助。