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      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 (at) gmail.com)
     13 
     14 #include <assert.h>
     15 #include <stdlib.h>
     16 #include "./rescaler.h"
     17 
     18 //------------------------------------------------------------------------------
     19 
     20 #if defined(__cplusplus) || defined(c_plusplus)
     21 extern "C" {
     22 #endif
     23 
     24 #define RFIX 30
     25 #define MULT_FIX(x, y) (((int64_t)(x) * (y) + (1 << (RFIX - 1))) >> RFIX)
     26 
     27 void WebPRescalerInit(WebPRescaler* const wrk, int src_width, int src_height,
     28                       uint8_t* const dst, int dst_width, int dst_height,
     29                       int dst_stride, int num_channels, int x_add, int x_sub,
     30                       int y_add, int y_sub, int32_t* const work) {
     31   wrk->x_expand = (src_width < dst_width);
     32   wrk->src_width = src_width;
     33   wrk->src_height = src_height;
     34   wrk->dst_width = dst_width;
     35   wrk->dst_height = dst_height;
     36   wrk->dst = dst;
     37   wrk->dst_stride = dst_stride;
     38   wrk->num_channels = num_channels;
     39   // for 'x_expand', we use bilinear interpolation
     40   wrk->x_add = wrk->x_expand ? (x_sub - 1) : x_add - x_sub;
     41   wrk->x_sub = wrk->x_expand ? (x_add - 1) : x_sub;
     42   wrk->y_accum = y_add;
     43   wrk->y_add = y_add;
     44   wrk->y_sub = y_sub;
     45   wrk->fx_scale = (1 << RFIX) / x_sub;
     46   wrk->fy_scale = (1 << RFIX) / y_sub;
     47   wrk->fxy_scale = wrk->x_expand ?
     48       ((int64_t)dst_height << RFIX) / (x_sub * src_height) :
     49       ((int64_t)dst_height << RFIX) / (x_add * src_height);
     50   wrk->irow = work;
     51   wrk->frow = work + num_channels * dst_width;
     52 }
     53 
     54 void WebPRescalerImportRow(WebPRescaler* const wrk,
     55                            const uint8_t* const src, int channel) {
     56   const int x_stride = wrk->num_channels;
     57   const int x_out_max = wrk->dst_width * wrk->num_channels;
     58   int x_in = channel;
     59   int x_out;
     60   int accum = 0;
     61   if (!wrk->x_expand) {
     62     int sum = 0;
     63     for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
     64       accum += wrk->x_add;
     65       for (; accum > 0; accum -= wrk->x_sub) {
     66         sum += src[x_in];
     67         x_in += x_stride;
     68       }
     69       {        // Emit next horizontal pixel.
     70         const int32_t base = src[x_in];
     71         const int32_t frac = base * (-accum);
     72         x_in += x_stride;
     73         wrk->frow[x_out] = (sum + base) * wrk->x_sub - frac;
     74         // fresh fractional start for next pixel
     75         sum = (int)MULT_FIX(frac, wrk->fx_scale);
     76       }
     77     }
     78   } else {        // simple bilinear interpolation
     79     int left = src[channel], right = src[channel];
     80     for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
     81       if (accum < 0) {
     82         left = right;
     83         x_in += x_stride;
     84         right = src[x_in];
     85         accum += wrk->x_add;
     86       }
     87       wrk->frow[x_out] = right * wrk->x_add + (left - right) * accum;
     88       accum -= wrk->x_sub;
     89     }
     90   }
     91   // Accumulate the new row's contribution
     92   for (x_out = channel; x_out < x_out_max; x_out += x_stride) {
     93     wrk->irow[x_out] += wrk->frow[x_out];
     94   }
     95 }
     96 
     97 uint8_t* WebPRescalerExportRow(WebPRescaler* const wrk) {
     98   if (wrk->y_accum <= 0) {
     99     int x_out;
    100     uint8_t* const dst = wrk->dst;
    101     int32_t* const irow = wrk->irow;
    102     const int32_t* const frow = wrk->frow;
    103     const int yscale = wrk->fy_scale * (-wrk->y_accum);
    104     const int x_out_max = wrk->dst_width * wrk->num_channels;
    105 
    106     for (x_out = 0; x_out < x_out_max; ++x_out) {
    107       const int frac = (int)MULT_FIX(frow[x_out], yscale);
    108       const int v = (int)MULT_FIX(irow[x_out] - frac, wrk->fxy_scale);
    109       dst[x_out] = (!(v & ~0xff)) ? v : (v < 0) ? 0 : 255;
    110       irow[x_out] = frac;   // new fractional start
    111     }
    112     wrk->y_accum += wrk->y_add;
    113     wrk->dst += wrk->dst_stride;
    114     return dst;
    115   } else {
    116     return NULL;
    117   }
    118 }
    119 
    120 #undef MULT_FIX
    121 #undef RFIX
    122 
    123 //------------------------------------------------------------------------------
    124 // all-in-one calls
    125 
    126 int WebPRescalerImport(WebPRescaler* const wrk, int num_lines,
    127                        const uint8_t* src, int src_stride) {
    128   int total_imported = 0;
    129   while (total_imported < num_lines && wrk->y_accum > 0) {
    130     int channel;
    131     for (channel = 0; channel < wrk->num_channels; ++channel) {
    132       WebPRescalerImportRow(wrk, src, channel);
    133     }
    134     src += src_stride;
    135     ++total_imported;
    136     wrk->y_accum -= wrk->y_sub;
    137   }
    138   return total_imported;
    139 }
    140 
    141 int WebPRescalerExport(WebPRescaler* const rescaler) {
    142   int total_exported = 0;
    143   while (WebPRescalerHasPendingOutput(rescaler)) {
    144     WebPRescalerExportRow(rescaler);
    145     ++total_exported;
    146   }
    147   return total_exported;
    148 }
    149 
    150 //------------------------------------------------------------------------------
    151 
    152 #if defined(__cplusplus) || defined(c_plusplus)
    153 }    // extern "C"
    154 #endif
    155