// Copyright 2011 Google Inc. All Rights Reserved.

//

// Use of this source code is governed by a BSD-style license

// that can be found in the COPYING file in the root of the source

// tree. An additional intellectual property rights grant can be found

// in the file PATENTS. All contributing project authors may

// be found in the AUTHORS file in the root of the source tree.

// -----------------------------------------------------------------------------

//

// filter estimation

//

// Author: Urvang (urvang@google.com)

#include "src/utils/filters_utils.h"

#include <stdlib.h>

#include <string.h>

// -----------------------------------------------------------------------------

// Quick estimate of a potentially interesting filter mode to try.

#define SMAX 16

#define SDIFF(a, b) (abs((a) - (b)) >> 4)   // Scoring diff, in [0..SMAX)

static WEBP_INLINE int GradientPredictor(uint8_t a, uint8_t b, uint8_t c) {

  const int g = a + b - c;

  return ((g & ~0xff) == 0) ? g : (g < 0) ? 0 : 255;  // clip to 8bit

}

WEBP_FILTER_TYPE WebPEstimateBestFilter(const uint8_t* data,

                                        int width, int height, int stride) {

  int i, j;

  int bins[WEBP_FILTER_LAST][SMAX];

  memset(bins, 0, sizeof(bins));

  // We only sample every other pixels. That's enough.

  for (j = 2; j < height - 1; j += 2) {

    const uint8_t* const p = data + j * stride;

    int mean = p[0];

    for (i = 2; i < width - 1; i += 2) {

      const int diff0 = SDIFF(p[i], mean);

      const int diff1 = SDIFF(p[i], p[i - 1]);

      const int diff2 = SDIFF(p[i], p[i - width]);

      const int grad_pred =

          GradientPredictor(p[i - 1], p[i - width], p[i - width - 1]);

      const int diff3 = SDIFF(p[i], grad_pred);

      bins[WEBP_FILTER_NONE][diff0] = 1;

      bins[WEBP_FILTER_HORIZONTAL][diff1] = 1;

      bins[WEBP_FILTER_VERTICAL][diff2] = 1;

      bins[WEBP_FILTER_GRADIENT][diff3] = 1;

      mean = (3 * mean + p[i] + 2) >> 2;

    }

  }

  {

    int filter;

    WEBP_FILTER_TYPE best_filter = WEBP_FILTER_NONE;

    int best_score = 0x7fffffff;

    for (filter = WEBP_FILTER_NONE; filter < WEBP_FILTER_LAST; ++filter) {

      int score = 0;

      for (i = 0; i < SMAX; ++i) {

        if (bins[filter][i] > 0) {

          score += i;

        }

      }

      if (score < best_score) {

        best_score = score;

        best_filter = (WEBP_FILTER_TYPE)filter;

      }

    }

    return best_filter;

  }

}

#undef SMAX

#undef SDIFF

//------------------------------------------------------------------------------