// Copyright 2013 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.

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

//

// Implement gradient smoothing: we replace a current alpha value by its

// surrounding average if it's close enough (that is: the change will be less

// than the minimum distance between two quantized level).

// We use sliding window for computing the 2d moving average.

//

// Author: Skal (pascal.massimino@gmail.com)

#include "src/utils/quant_levels_dec_utils.h"

#include <string.h>   // for memset

#include "src/utils/utils.h"

// #define USE_DITHERING   // uncomment to enable ordered dithering (not vital)

#define FIX 16     // fix-point precision for averaging

#define LFIX 2     // extra precision for look-up table

#define LUT_SIZE ((1 << (8 + LFIX)) - 1)  // look-up table size

#if defined(USE_DITHERING)

#define DFIX 4           // extra precision for ordered dithering

#define DSIZE 4          // dithering size (must be a power of two)

// cf. http://en.wikipedia.org/wiki/Ordered_dithering

static const uint8_t kOrderedDither[DSIZE][DSIZE] = {

  {  0,  8,  2, 10 },     // coefficients are in DFIX fixed-point precision

  { 12,  4, 14,  6 },

  {  3, 11,  1,  9 },

  { 15,  7, 13,  5 }

};

#else

#define DFIX 0

#endif

typedef struct {

  int width_, height_;  // dimension

  int stride_;          // stride in bytes

  int row_;             // current input row being processed

  uint8_t* src_;        // input pointer

  uint8_t* dst_;        // output pointer

  int radius_;          // filter radius (=delay)

  int scale_;           // normalization factor, in FIX bits precision

  void* mem_;           // all memory

  // various scratch buffers

  uint16_t* start_;

  uint16_t* cur_;

  uint16_t* end_;

  uint16_t* top_;

  uint16_t* average_;

  // input levels distribution

  int num_levels_;       // number of quantized levels

  int min_, max_;        // min and max level values

  int min_level_dist_;   // smallest distance between two consecutive levels

  int16_t* correction_;  // size = 1 + 2*LUT_SIZE  -> ~4k memory

} SmoothParams;

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

#define CLIP_8b_MASK (int)(~0U << (8 + DFIX))

static WEBP_INLINE uint8_t clip_8b(int v) {

  return (!(v & CLIP_8b_MASK)) ? (uint8_t)(v >> DFIX) : (v < 0) ? 0u : 255u;

}

#undef CLIP_8b_MASK

// vertical accumulation

static void VFilter(SmoothParams* const p) {

  const uint8_t* src = p->src_;

  const int w = p->width_;

  uint16_t* const cur = p->cur_;

  const uint16_t* const top = p->top_;

  uint16_t* const out = p->end_;

  uint16_t sum = 0;               // all arithmetic is modulo 16bit

  int x;

  for (x = 0; x < w; ++x) {

    uint16_t new_value;

    sum += src[x];

    new_value = top[x] + sum;

    out[x] = new_value - cur[x];  // vertical sum of 'r' pixels.

    cur[x] = new_value;

  }

  // move input pointers one row down

  p->top_ = p->cur_;

  p->cur_ += w;

  if (p->cur_ == p->end_) p->cur_ = p->start_;  // roll-over

  // We replicate edges, as it's somewhat easier as a boundary condition.

  // That's why we don't update the 'src' pointer on top/bottom area:

  if (p->row_ >= 0 && p->row_ < p->height_ - 1) {

    p->src_ += p->stride_;

  }

}

// horizontal accumulation. We use mirror replication of missing pixels, as it's

// a little easier to implement (surprisingly).

static void HFilter(SmoothParams* const p) {

  const uint16_t* const in = p->end_;

  uint16_t* const out = p->average_;

  const uint32_t scale = p->scale_;

  const int w = p->width_;

  const int r = p->radius_;

  int x;

  for (x = 0; x <= r; ++x) {   // left mirroring

    const uint16_t delta = in[x + r - 1] + in[r - x];

    out[x] = (delta * scale) >> FIX;

  }

  for (; x < w - r; ++x) {     // bulk middle run

    const uint16_t delta = in[x + r] - in[x - r - 1];

    out[x] = (delta * scale) >> FIX;

  }

  for (; x < w; ++x) {         // right mirroring

    const uint16_t delta =

        2 * in[w - 1] - in[2 * w - 2 - r - x] - in[x - r - 1];

    out[x] = (delta * scale) >> FIX;

  }

}

// emit one filtered output row

static void ApplyFilter(SmoothParams* const p) {

  const uint16_t* const average = p->average_;

  const int w = p->width_;

  const int16_t* const correction = p->correction_;

#if defined(USE_DITHERING)

  const uint8_t* const dither = kOrderedDither[p->row_ % DSIZE];

#endif

  uint8_t* const dst = p->dst_;

  int x;

  for (x = 0; x < w; ++x) {

    const int v = dst[x];

    if (v < p->max_ && v > p->min_) {

      const int c = (v << DFIX) + correction[average[x] - (v << LFIX)];

#if defined(USE_DITHERING)

      dst[x] = clip_8b(c + dither[x % DSIZE]);

#else

      dst[x] = clip_8b(c);

#endif

    }

  }

  p->dst_ += p->stride_;  // advance output pointer

}

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

// Initialize correction table

static void InitCorrectionLUT(int16_t* const lut, int min_dist) {

  // The correction curve is:

  //   f(x) = x for x <= threshold2

  //   f(x) = 0 for x >= threshold1

  // and a linear interpolation for range x=[threshold2, threshold1]

  // (along with f(-x) = -f(x) symmetry).

  // Note that: threshold2 = 3/4 * threshold1

  const int threshold1 = min_dist << LFIX;

  const int threshold2 = (3 * threshold1) >> 2;

  const int max_threshold = threshold2 << DFIX;

  const int delta = threshold1 - threshold2;

  int i;

  for (i = 1; i <= LUT_SIZE; ++i) {

    int c = (i <= threshold2) ? (i << DFIX)

          : (i < threshold1) ? max_threshold * (threshold1 - i) / delta

          : 0;

    c >>= LFIX;

    lut[+i] = +c;

    lut[-i] = -c;

  }

  lut[0] = 0;

}

static void CountLevels(SmoothParams* const p) {

  int i, j, last_level;

  uint8_t used_levels[256] = { 0 };

  const uint8_t* data = p->src_;

  p->min_ = 255;

  p->max_ = 0;

  for (j = 0; j < p->height_; ++j) {

    for (i = 0; i < p->width_; ++i) {

      const int v = data[i];

      if (v < p->min_) p->min_ = v;

      if (v > p->max_) p->max_ = v;

      used_levels[v] = 1;

    }

    data += p->stride_;

  }

  // Compute the mininum distance between two non-zero levels.

  p->min_level_dist_ = p->max_ - p->min_;

  last_level = -1;

  for (i = 0; i < 256; ++i) {

    if (used_levels[i]) {

      ++p->num_levels_;

      if (last_level >= 0) {

        const int level_dist = i - last_level;

        if (level_dist < p->min_level_dist_) {

          p->min_level_dist_ = level_dist;

        }

      }

      last_level = i;

    }

  }

}

// Initialize all params.

static int InitParams(uint8_t* const data, int width, int height, int stride,

                      int radius, SmoothParams* const p) {

  const int R = 2 * radius + 1;  // total size of the kernel

  const size_t size_scratch_m = (R + 1) * width * sizeof(*p->start_);

  const size_t size_m =  width * sizeof(*p->average_);

  const size_t size_lut = (1 + 2 * LUT_SIZE) * sizeof(*p->correction_);

  const size_t total_size = size_scratch_m + size_m + size_lut;

  uint8_t* mem = (uint8_t*)WebPSafeMalloc(1U, total_size);

  if (mem == NULL) return 0;

  p->mem_ = (void*)mem;

  p->start_ = (uint16_t*)mem;

  p->cur_ = p->start_;

  p->end_ = p->start_ + R * width;

  p->top_ = p->end_ - width;

  memset(p->top_, 0, width * sizeof(*p->top_));

  mem += size_scratch_m;

  p->average_ = (uint16_t*)mem;

  mem += size_m;

  p->width_ = width;

  p->height_ = height;

  p->stride_ = stride;

  p->src_ = data;

  p->dst_ = data;

  p->radius_ = radius;

  p->scale_ = (1 << (FIX + LFIX)) / (R * R);  // normalization constant

  p->row_ = -radius;

  // analyze the input distribution so we can best-fit the threshold

  CountLevels(p);

  // correction table

  p->correction_ = ((int16_t*)mem) + LUT_SIZE;

  InitCorrectionLUT(p->correction_, p->min_level_dist_);

  return 1;

}

static void CleanupParams(SmoothParams* const p) {

  WebPSafeFree(p->mem_);

}

int WebPDequantizeLevels(uint8_t* const data, int width, int height, int stride,

                         int strength) {

  const int radius = 4 * strength / 100;

  if (strength < 0 || strength > 100) return 0;

  if (data == NULL || width <= 0 || height <= 0) return 0;  // bad params

  if (radius > 0) {

    SmoothParams p;

    memset(&p, 0, sizeof(p));

    if (!InitParams(data, width, height, stride, radius, &p)) return 0;

    if (p.num_levels_ > 2) {

      for (; p.row_ < p.height_; ++p.row_) {

        VFilter(&p);  // accumulate average of input

        // Need to wait few rows in order to prime the filter,

        // before emitting some output.

        if (p.row_ >= p.radius_) {

          HFilter(&p);

          ApplyFilter(&p);

        }

      }

    }

    CleanupParams(&p);

  }

  return 1;

}