Page Speed Optimization Libraries  1.9.32.2
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net_instaweb::LazyloadImagesFilter Class Reference

#include "lazyload_images_filter.h"

Inheritance diagram for net_instaweb::LazyloadImagesFilter:
net_instaweb::CommonFilter

Public Member Functions

 LazyloadImagesFilter (RewriteDriver *driver)
 
virtual const char * Name () const
 
- Public Member Functions inherited from net_instaweb::CommonFilter
 CommonFilter (RewriteDriver *driver)
 
const GoogleUrl & base_url () const
 Getters. More...
 
const GoogleUrl & decoded_base_url () const
 
RewriteDriverdriver () const
 
HtmlElement * noscript_element () const
 
void InsertNodeAtBodyEnd (HtmlNode *data)
 
virtual void StartDocument ()
 Note: Don't overload these methods, overload the implementers instead!
 
virtual void StartElement (HtmlElement *element)
 
virtual void EndElement (HtmlElement *element)
 
virtual void Characters (HtmlCharactersNode *characters)
 
ResourcePtr CreateInputResource (StringPiece input_url, bool *is_authorized)
 
ResourcePtr CreateInputResourceOrInsertDebugComment (StringPiece input_url, HtmlElement *element)
 
void ResolveUrl (StringPiece input_url, GoogleUrl *out_url)
 
bool BaseUrlIsValid () const
 
bool DebugMode () const
 
bool CanAddPagespeedOnloadToImage (const HtmlElement &)
 
virtual void LogFilterModifiedContent ()
 
virtual
RewriteDriver::InlineAuthorizationPolicy 
AllowUnauthorizedDomain () const
 
virtual bool IntendedForInlining () const
 

Static Public Member Functions

static void InitStats (Statistics *statistics)
 
static void Terminate ()
 
static
RewriterHtmlApplication::Status 
ShouldApply (RewriteDriver *driver)
 Lazyload filter will be no op for the request if ShouldApply returns false.
 
static GoogleString GetLazyloadJsSnippet (const RewriteOptions *options, StaticAssetManager *static_asset_manager)
 
- Static Public Member Functions inherited from net_instaweb::CommonFilter
static bool ExtractMetaTagDetails (const HtmlElement &element, const ResponseHeaders *headers, GoogleString *content, GoogleString *mime_type, GoogleString *charset)
 

Static Public Attributes

static const char * kImageLazyloadCode
 
static const char * kImageOnloadCode
 
static const char * kLoadAllImages
 
static const char * kOverrideAttributeFunctions
 
static const char * kIsLazyloadScriptInsertedPropertyName
 
- Static Public Attributes inherited from net_instaweb::CommonFilter
static const char kCreateResourceFailedDebugMsg []
 Debug message to be inserted when resource creation fails.
 

Additional Inherited Members

- Protected Member Functions inherited from net_instaweb::CommonFilter
ServerContextserver_context () const
 
const RewriteOptionsrewrite_options ()
 
virtual const char * LoggingId ()
 

Detailed Description

Filter to lazyload images by replacing the src with a pagespeed_lazy_src attribute and injecting a javascript to detect which images are in the user's viewport and swapping the src back.

This filter only works if the document has a head. It adds some javascript to the head that determines if an image is visible and adds a listener to the window scroll event. If an image is visible, it replaces the src and the pagespeed_lazy_src attributes.

In order to immediately load images that are above the fold, we attach an onload event to each image. This onload event determines if the image is visible and immediately replaces the src with the pagespeed_lazy_src. Otherwise, the image is added to the deferred queue. Since the onload event is only fired if the image src is valid, we add a fixed inlined image to each image node we are deferring.

When the user scrolls, we scan through the deferred queue and determine which images are now visible, and switch the src and pagespeed_lazy_src.

Given the following input html: <html> <head> </head> <body>

</body> </html>

The output will be <html> <head> <script> Javascript that determines which images are visible and attaches a window.scroll event. </script> </head> <body>

</body>


The documentation for this class was generated from the following file: