third_party/libwebp/utils/rescaler.c

   1 // Copyright 2012 Google Inc. All Rights Reserved.
   2 //
   3 // Use of this source code is governed by a BSD-style license
   4 // that can be found in the COPYING file in the root of the source
   5 // tree. An additional intellectual property rights grant can be found
   6 // in the file PATENTS. All contributing project authors may
   7 // be found in the AUTHORS file in the root of the source tree.
   8 // -----------------------------------------------------------------------------
   9 //
  10 // Rescaling functions
  11 //
  12 // Author: Skal (pascal.massimino@gmail.com)
  13
  14 #include <assert.h>
  15 #include <stdlib.h>
  16 #include "./rescaler.h"
  17
  18 //------------------------------------------------------------------------------
  19
  20 #define RFIX 30
  21 #define MULT_FIX(x, y) (((int64_t)(x) * (y) + (1 << (RFIX - 1))) >> RFIX)
  22
  23 void WebPRescalerInit(WebPRescaler* const wrk, int src_width, int src_height,
  24                       uint8_t* const dst, int dst_width, int dst_height,
  25                       int dst_stride, int num_channels, int x_add, int x_sub,
  26                       int y_add, int y_sub, int32_t* const work) {
  27   wrk->x_expand = (src_width < dst_width);
  28   wrk->src_width = src_width;
  29   wrk->src_height = src_height;
  30   wrk->dst_width = dst_width;
  31   wrk->dst_height = dst_height;
  32   wrk->dst = dst;
  33   wrk->dst_stride = dst_stride;
  34   wrk->num_channels = num_channels;
  35   // for 'x_expand', we use bilinear interpolation
  36   wrk->x_add = wrk->x_expand ? (x_sub - 1) : x_add - x_sub;
  37   wrk->x_sub = wrk->x_expand ? (x_add - 1) : x_sub;
  38   wrk->y_accum = y_add;
  39   wrk->y_add = y_add;
  40   wrk->y_sub = y_sub;
  41   wrk->fx_scale = (1 << RFIX) / x_sub;
  42   wrk->fy_scale = (1 << RFIX) / y_sub;
  43   wrk->fxy_scale = wrk->x_expand ?
  44       ((int64_t)dst_height << RFIX) / (x_sub * src_height) :
  45       ((int64_t)dst_height << RFIX) / (x_add * src_height);
  46   wrk->irow = work;
  47   wrk->frow = work + num_channels * dst_width;
  48 }
  49
  50 void WebPRescalerImportRow(WebPRescaler* const wrk,
  51                            const uint8_t* const src, int channel) {
  52   const int x_stride = wrk->num_channels;
  53   const int x_out_max = wrk->dst_width * wrk->num_channels;
  54   int x_in = channel;
  55   int x_out;
  56   int accum = 0;
  57   if (!wrk->x_expand) {
  58     int sum = 0;
  59     for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
  60       accum += wrk->x_add;
  61       for (; accum > 0; accum -= wrk->x_sub) {
  62         sum += src[x_in];
  63         x_in += x_stride;
  64       }
  65       {        // Emit next horizontal pixel.
  66         const int32_t base = src[x_in];
  67         const int32_t frac = base * (-accum);
  68         x_in += x_stride;
  69         wrk->frow[x_out] = (sum + base) * wrk->x_sub - frac;
  70         // fresh fractional start for next pixel
  71         sum = (int)MULT_FIX(frac, wrk->fx_scale);
  72       }
  73     }
  74   } else {        // simple bilinear interpolation
  75     int left = src[channel], right = src[channel];
  76     for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
  77       if (accum < 0) {
  78         left = right;
  79         x_in += x_stride;
  80         right = src[x_in];
  81         accum += wrk->x_add;
  82       }
  83       wrk->frow[x_out] = right * wrk->x_add + (left - right) * accum;
  84       accum -= wrk->x_sub;
  85     }
  86   }
  87   // Accumulate the new row's contribution
  88   for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
  89     wrk->irow[x_out] += wrk->frow[x_out];
  90   }
  91 }
  92
  93 uint8_t* WebPRescalerExportRow(WebPRescaler* const wrk) {
  94   if (wrk->y_accum <= 0) {
  95     int x_out;
  96     uint8_t* const dst = wrk->dst;
  97     int32_t* const irow = wrk->irow;
  98     const int32_t* const frow = wrk->frow;
  99     const int yscale = wrk->fy_scale * (-wrk->y_accum);
 100     const int x_out_max = wrk->dst_width * wrk->num_channels;
 101
 102     for (x_out = 0; x_out < x_out_max; ++x_out) {
 103       const int frac = (int)MULT_FIX(frow[x_out], yscale);
 104       const int v = (int)MULT_FIX(irow[x_out] - frac, wrk->fxy_scale);
 105       dst[x_out] = (!(v & ~0xff)) ? v : (v < 0) ? 0 : 255;
 106       irow[x_out] = frac;   // new fractional start
 107     }
 108     wrk->y_accum += wrk->y_add;
 109     wrk->dst += wrk->dst_stride;
 110     return dst;
 111   } else {
 112     return NULL;
 113   }
 114 }
 115
 116 #undef MULT_FIX
 117 #undef RFIX
 118
 119 //------------------------------------------------------------------------------
 120 // all-in-one calls
 121
 122 int WebPRescaleNeededLines(const WebPRescaler* const wrk, int max_num_lines) {
 123   const int num_lines = (wrk->y_accum + wrk->y_sub - 1) / wrk->y_sub;
 124   return (num_lines > max_num_lines) ? max_num_lines : num_lines;
 125 }
 126
 127 int WebPRescalerImport(WebPRescaler* const wrk, int num_lines,
 128                        const uint8_t* src, int src_stride) {
 129   int total_imported = 0;
 130   while (total_imported < num_lines && wrk->y_accum > 0) {
 131     int channel;
 132     for (channel = 0; channel < wrk->num_channels; ++channel) {
 133       WebPRescalerImportRow(wrk, src, channel);
 134     }
 135     src += src_stride;
 136     ++total_imported;
 137     wrk->y_accum -= wrk->y_sub;
 138   }
 139   return total_imported;
 140 }
 141
 142 int WebPRescalerExport(WebPRescaler* const rescaler) {
 143   int total_exported = 0;
 144   while (WebPRescalerHasPendingOutput(rescaler)) {
 145     WebPRescalerExportRow(rescaler);
 146     ++total_exported;
 147   }
 148   return total_exported;
 149 }
 150
 151 //------------------------------------------------------------------------------
 152