text: /*
   * Copyright 2016 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.
   */
  
  #ifndef GUETZLI_COMPARATOR_H_
  #define GUETZLI_COMPARATOR_H_
  
  #include <vector>
  
  #include "guetzli/output_image.h"
  #include "guetzli/stats.h"
  
  namespace guetzli {
  
  // Represents a baseline image, a comparison metric and an image acceptance
  // criteria based on this metric.
  class Comparator {
   public:
    Comparator() {}
    virtual ~Comparator() {}
  
    // Compares img with the baseline image and saves the resulting distance map
    // inside the object. The provided image must have the same dimensions as the
    // baseline image.
    virtual void Compare(const OutputImage& img) = 0;
  
    // Must be called before any CompareBlock() calls can be called.
    virtual void StartBlockComparisons() = 0;
    // No more CompareBlock() calls can be called after this.
    virtual void FinishBlockComparisons() = 0;
  
    // Sets the coordinates of the current macro-block for the purpose of
    // CompareBlock() calls.
    virtual void SwitchBlock(int block_x, int block_y,
                             int factor_x, int factor_y) = 0;
  
    // Compares the 8x8 block with offsets (off_x, off_y) within the current
    // macro-block of the baseline image with the same block of img and returns
    // the resulting per-block distance. The interpretation of the returned
    // distance depends on the comparator used.
    virtual double CompareBlock(const OutputImage& img,
                                int off_x, int off_y, const coeff_t* candidate_block, const int comp_mask) const = 0;
  
    // Returns the combined score of the output image in the last Compare() call
    // (or the baseline image, if Compare() was not called yet), based on output
    // size and the similarity metric.
    virtual double ScoreOutputSize(int size) const = 0;
  
    // Returns true if the argument of the last Compare() call (or the baseline
    // image, if Compare() was not called yet) meets the image acceptance
    // criteria. The target_mul modifies the acceptance criteria used in this call
    // the following way:
    //    = 1.0 : the original acceptance criteria is used,
    //    < 1.0 : a more strict acceptance criteria is used,
    //    > 1.0 : a less strict acceptance criteria is used.
    virtual bool DistanceOK(double target_mul) const = 0;
  
    // Returns the distance map between the baseline image and the image in the
    // last Compare() call (or the baseline image, if Compare() was not called
    // yet).
    // The dimensions of the distance map are the same as the baseline image.
    // The interpretation of the distance values depend on the comparator used.
    virtual const std::vector<float> distmap() const = 0;
  
    // Returns an aggregate distance or similarity value between the baseline
    // image and the image in the last Compare() call (or the baseline image, if
    // Compare() was not called yet).
    // The interpretation of this aggregate value depends on the comparator used.
    virtual float distmap_aggregate() const = 0;
  
    // Returns a heuristic cutoff on block errors in the sense that we won't
    // consider distortions where a block error is greater than this.
    virtual float BlockErrorLimit() const = 0;
    // Given the search direction (+1 for upwards and -1 for downwards) and the
    // current distance map, fills in *block_weight image with the relative block
    // error adjustment weights.
    // The target_mul param has the same semantics as in DistanceOK().
    // Note that this is essentially a static function in the sense that it does
    // not depend on the last Compare() call.
    virtual void ComputeBlockErrorAdjustmentWeights(
        int direction, int max_block_dist, double target_mul, int factor_x,
        int factor_y, const std::vector<float>& distmap,
        std::vector<float>* block_weight) = 0;
  };
  
  
  }  // namespace guetzli
  
  #endif  // GUETZLI_COMPARATOR_H_
  