src/net/instaweb/rewriter/public/image_combine_filter.h

/*
 * Copyright 2011 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// Author: abliss@google.com (Adam Bliss)

#ifndef NET_INSTAWEB_REWRITER_PUBLIC_IMAGE_COMBINE_FILTER_H_
#define NET_INSTAWEB_REWRITER_PUBLIC_IMAGE_COMBINE_FILTER_H_

#include "net/instaweb/rewriter/public/css_filter.h"
#include "net/instaweb/rewriter/public/rewrite_filter.h"
#include "net/instaweb/rewriter/public/rewrite_options.h"
#include "net/instaweb/rewriter/public/server_context.h"
#include "pagespeed/kernel/base/basictypes.h"
#include "pagespeed/kernel/base/string_util.h"
#include "pagespeed/kernel/util/url_multipart_encoder.h"

namespace Css {

class Declarations;
class Values;

}  // namespace Css

namespace net_instaweb {

class GoogleUrl;
class HtmlElement;
class MessageHandler;
class RewriteContext;
class RewriteDriver;
class Statistics;
class UrlSegmentEncoder;
class Variable;

/*
 * The ImageCombineFilter combines multiple images into a single image
 * (a process called "spriting".  This reduces the total number of
 * round-trips, and reduces bytes downloaded by consolidating image
 * headers and improving compression.
 *
 * Right now this is only used on CSS background-images, so it doesn't
 * need to be in the HTML filter chain.  In the future it will rewrite
 * img tags as well.
 */
class ImageCombineFilter : public RewriteFilter {
 public:
  explicit ImageCombineFilter(RewriteDriver* rewrite_driver);
  virtual ~ImageCombineFilter();

  static void InitStats(Statistics* statistics);

  // Attempt to add the CSS background image with (resolved) url original_url to
  // this partnership.  We do not take ownership of declarations; it must live
  // until you call Realize() or Reset().  declarations is where we will add the
  // new width and height values; url_value must point to the URL value to be
  // replaced. Will not actually change anything until you call Realize().
  // This will succeed even in cases when it turns out (later) the image
  // can not be sprited. Fails and returns false if:
  // * We cannot get the declaration dimensions from 'decls'.
  // * original_url is not on an authorized domain.
  // * There is already a slot for original_url.
  bool AddCssBackgroundContext(const GoogleUrl& original_url,
                               const GoogleUrl& base_url,
                               Css::Values* values,
                               int value_index,
                               CssFilter::Context* parent,
                               Css::Declarations* decls,
                               bool* is_authorized,
                               MessageHandler* handler);

  // Create the combination with the current combiner.
  OutputResourcePtr MakeOutput();

  // Creates a new context for doing spriting, but does not register it.
  void Reset(RewriteContext* context, const GoogleUrl& css_url,
             const StringPiece& css_text);

  // If there is any work to do, registers the RewriteContext created by
  // Reset(). If there isn't, cleans it up.
  void RegisterOrReleaseContext();

 protected:
  virtual const UrlSegmentEncoder* encoder() const { return &encoder_; }
  virtual const char* Name() const { return "ImageCombine"; }
  virtual void StartDocumentImpl() {}
  virtual void StartElementImpl(HtmlElement* element) {}
  virtual void EndElementImpl(HtmlElement* element) {}

  // Image rewriting was originally, but is no longer, a single CSS.
  virtual const char* id() const { return RewriteOptions::kImageCombineId; }

 private:
  class Combiner;
  class Context;

  virtual RewriteContext* MakeRewriteContext();
  Context* MakeNestedContext(RewriteContext* parent, const GoogleUrl& css_url,
                             const StringPiece& css_text);
  bool GetDeclarationDimensions(Css::Declarations* declarations,
                                int* width, int* height);
  void AddFilesReducedStat(int reduced);

  Variable* image_file_count_reduction_;
  Context* context_;
  UrlMultipartEncoder encoder_;

  DISALLOW_COPY_AND_ASSIGN(ImageCombineFilter);
};

}  // namespace net_instaweb

#endif  // NET_INSTAWEB_REWRITER_PUBLIC_IMAGE_COMBINE_FILTER_H_