Phpheader function outputs image cache implementation code

Phpheader function outputs image cache implementation code

// 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 "))); Add this code in header ("Content-type: image/jpeg"), which specifies the current page cache time (two days ), the cache time node is used in the next access. Next, determine whether a cache exists. If yes, use the cache. Scenario 1: If the browser already caches the current page, use it directly. // 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; } Case 2: The browser caches the current page. although some image information is updated, the source image itself remains unchanged and you want to use the previous cache. $ 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; } Of course, we have to consider some special cases. remember to put them on the header ("Content-type: image/jpeg. Example: // Adjust the image size /** * How images are adjusted proportionally: * 1. compare whether the source image size is smaller than or equal to the target size. If yes, directly use the source image width and height. * 2. if the source image size exceeds the target size, the source image width and height are compared. * 3. for example, if the width is greater than the height, the width = the target width and the height = the proportion of the target width * the original height * 4. for example: height> width, the ratio of height to target height and width to target height * original width **/Bbs.it-home.org $ Image = "test.jpg "; $ Max_width = 200; $ Max_height = 200; $ Size = getimagesize ($ image); // Obtain the image size. $ 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); // create a true color image Imagecopyresampled ($ dst, $ src, 0, 0, 0, $ tn_width, $ tn_height, $ width, $ height); // Copy part of the image and resize it. Header ('content-Type: image/jpeg '); Imagejpeg ($ dst, null, 100 ); Imagedestroy ($ src ); Imagedestroy ($ dst ); ?>