php动态生成图片实现浏览器缓存

青旅半醒 2022-07-12 10:26 293阅读 0赞

当我们用php实现网站图片尺寸重写时，默认情况下浏览器不会将重写的图片缓存本地，现在我告诉你们怎样让浏览器缓存这样的图片数据。  
// 在php脚本文件加上以下代码

session_start(); 
    header("Cache-Control: private, max-age=10800, pre-check=10800");
    header("Pragma: private");
    header("Expires: " . date(DATE_RFC822,strtotime(" 2 day")));

1:如果浏览器已经有缓存版本，它会向后端传一个$\_SERVER\[‘HTTP\_IF\_MODIFIED\_SINCE’\] ，简单的做法我们只需要告诉浏览器用缓存即可。

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;
    }

2:如果浏览器有缓存版本，更明智的做法是，后端判断图片有没有更新，对应告知浏览器是否用缓存版本

$img = "some_image.png";
    if (isset($_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;
    }

完整的代码

session_start(); 
    header("Cache-Control: private, max-age=10800, pre-check=10800");
    header("Pragma: private");
    header("Expires: " . date(DATE_RFC822,strtotime(" 2 day")));
    $img = "some_image.png"; 
    if (isset($_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;
    }

// 裁剪图片，并且告知浏览器缓存图片

$is = new ImageSizer($img); 
    $is->resizeImage(75); // resize image to 75px wide
    // and here we send the image to the browser with all the stuff required for tell it to cache
    header("Content-type: image/jpeg");
    header('Last-Modified: ' . gmdate('D, d M Y H:i:s', filemtime($thumbnail)) . ' GMT');
    $is->showImage();

图片裁剪类

class ImageSizer { 
    
      var $_baseDir;
      var $_baseImg;
      var $_imgData;
    
      var $_newImg;
      var $_newData;
      var $_newFormat;
    
      var $_loadPath;
      var $_defaultColor = array(255,255,255);
    
      var $keepAspectRatio;
      var $makeBigger;
    
      function ImageSizer($baseDir) { 
        $this->changeBaseDir($baseDir);
        $this->keepAspectRatio = true;
        $this->makeBigger = false;
      }
    
      function changeBaseDir($baseDir) { 
        $this->_baseDir = $baseDir;
      }
    
      function setDefaultColor($r, $g, $b) { 
        $this->_defaultColor = array($r, $g, $b);
      }
    
      function changeFormat($str) { 
        $str = strtolower($str);
        if ($str == 'jpg') $str = "jpeg";
        $acceptable_formats = array('jpeg', 'gif', 'png');
        if (!in_array($str, $acceptable_formats)) return false;
        $this->_newFormat = $str;
      }
    
      function loadImage($imgPath) { 
       // $this->_imgData = getimagesize($this->_baseDir. $imgPath);
        $this->_imgData = getimagesize( $imgPath);
        $this->_imgData['funcType'] = preg_replace('#image/#i', '', $this->_imgData['mime']);
        $acceptable_formats = array('jpeg', 'gif', 'png');
        if (!in_array($this->_imgData['funcType'], $acceptable_formats)) return false;
        $this->_newData = $this->_imgData;
        $funcName = 'imagecreatefrom' . $this->_imgData['funcType'];
        //$this->_newImg = $this->_baseImg = $funcName($this->_baseDir. $imgPath);
        $this->_newImg = $this->_baseImg  = @$funcName( $imgPath);
        if(!$this->_baseImg){
            echo " Failed on this image $imgPath ";
            return false;
        }
        $this->_loadPath = $imgPath;
        return true;
      }
        /*function genImageData(){ $funcName = 'image'.$this->getNewType(); $data = $funcName($this->_newImg ? $this->_newImg : $this->_baseImg); return $data; }*/
      function resizeImage($w, $h, $crop=false) { 
        $current_w = $this->getWidth();
        $current_h = $this->getHeight();
    
        $src_x = $src_y = 0;
        $dst_x = $dst_y = 0;
    
        if($w && $h && $crop=="f"){
            // fill in the image centre it in white.
            // all the src stuff stays the same, just changing the destination suff
            $src_x = 0;
            $src_y = 0; 
            $current_h = $current_h;
            $current_w = $current_w;
    
            // the destination stuff changes
            if($h && $w){
                $h_percent = $percent = $h / $current_h;
                $w_percent = $percent = $w / $current_w;
                 $percent = min($h_percent, $w_percent);
            }else if($h){
                $h_percent = $percent = $h / $current_h;
                 $percent = $h_percent;
            }else if($w){
                $w_percent = $percent = $w / $current_w;
                 $percent = $w_percent;
            }
            $dst_w = $current_w * $percent;
            $dst_h = $current_h * $percent;
    
            $new_w = $w;
            $new_h = $h;
            // work out destination x and y points
    
            $dst_x = ($new_w - $dst_w)/2;
            $dst_y = ($new_h - $dst_h)/2;
    
        }else if($w && $h && $crop=="c"){
            $dst_w = $w;
            $dst_h = $h;
            $new_w = $w;
            $new_h = $h;
            // if the image we are tyring to crop is smaller than the crop request we dont do aynthing
            if($w > $current_w || $h > $current_h){
                // the image is smaller than we are trying to crop!
            }else{
                //the image is bigger on x and y axis.
                // check if we can fit horizontally
                $w_percent = $current_w/$w;
                $h_percent = $current_h/$h;
                if($w_percent < $h_percent){
                    $src_x = 0;
                    $src_y = ($current_h/2) - (($h * $w_percent)/2);
                    $current_w = $current_w;
                    $current_h = ($h * $w_percent);
                }else{
                    $src_x = ($current_w/2) - (($w * $h_percent)/2);
                    $src_y = 0;
                    $current_w = ($w * $h_percent);
                    $current_h = $current_h;
                }
    
            }
    
        }else if ($this->keepAspectRatio) {
          $percent = 1;
         // if ($current_w > $w || $current_h > $h || $this->makeBigger) { 
         $do_resize=false;
         if($w && $current_w > $w){
            $do_resize=true;
         }else if($h && $current_h > $h){
            $do_resize=true;
         }else if($w && $current_w < $w && $this->makeBigger){
            $do_resize=true;
         }else{
            // imaeg is alreaedy smaller than requested size
         }
          if (  $do_resize ) {
            if($h && $w){
                $h_percent = $percent = $h / $current_h;
                $w_percent = $percent = $w / $current_w;
                 $percent = min($h_percent, $w_percent);
            }else if($h){
                $h_percent = $percent = $h / $current_h;
                 $percent = $h_percent;
            }else if($w){
                $w_percent = $percent = $w / $current_w;
                 $percent = $w_percent;
            }
          }
    
            $dst_w = $new_w = $current_w * $percent;
            $dst_h = $new_h = $current_h * $percent;
        } else{
            $dst_w = $new_w = $w;
            $dst_h = $new_h = $h;
        }
    
        $this->_newImg = ImageCreateTrueColor($new_w, $new_h);
        $this->_newData = array($new_w, $new_h);
    
        if ($this->getNewType() == 'png' || $this->getNewType() == 'gif') { // This preserves the transparency
          imageAlphaBlending($this->_newImg, false);
          imageSaveAlpha($this->_newImg, true);
        } else { // This is if converting from PNG to another image format
          list($r, $g, $b) = $this->_defaultColor;
          $color = imagecolorallocate($this->_newImg, $r, $g, $b);
          imagefilledrectangle($this->_newImg, 0,0, $new_w, $new_h, $color);
        }
                                                                                        // dst_w dst_h src_w src_h
        imagecopyresampled($this->_newImg, $this->_baseImg, $dst_x, $dst_y,$src_x,$src_y, $dst_w, $dst_h, $current_w, $current_h);
        return true;
      }
    
      function showImage() { 
        header('Content-type: ' . $this->getNewMime());
        $funcName = 'image'.$this->getNewType();
        $funcName($this->_newImg ? $this->_newImg : $this->_baseImg);
      }
    
      function saveToFile($fileloc) { 
        $funcName = 'image'.$this->getNewType();
        $funcName($this->_newImg ? $this->_newImg : $this->_baseImg, $fileloc,100);
      }
    
      function addWatermark($pngloc,$offset_x=0) { 
        $overlay = imagecreatefrompng($pngloc);
        imageAlphaBlending($overlay, false);
        imageSaveAlpha($overlay, true);
        imagecopy($this->_newImg, $overlay, (imagesx($this->_newImg))-(imagesx($overlay)+$offset_x), (imagesy($this->_newImg))-(imagesy($overlay)), 0, 0, imagesx($overlay), imagesy($overlay));
      }
    
      function getBaseDir() {  return $this->_baseDir; }
    
      function getWidth() {  return $this->_imgData[0]; }
      function getHeight() {  return $this->_imgData[1]; }
      function getMime() {  return $this->_imgData['mime']; }
      function getType() {  return $this->_imgData['funcType'];}
    
    
      function getNewWidth() {  return $this->_newData[0]; }
      function getNewHeight() {  return $this->_newData[1]; }
      function getNewMime() { return $this->_newFormat ? 'image/' . $this->_newFormat : $this->_imgData['mime'];}
      function getNewType() { return $this->_newFormat ? $this->_newFormat : $this->_imgData['funcType'];}
    
    }