tor-browser

io_dec.c (24192B)

---

// 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.
// -----------------------------------------------------------------------------
//
// functions for sample output.
//
// Author: Skal (pascal.massimino@gmail.com)

#include <assert.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>

#include "src/dec/vp8_dec.h"
#include "src/webp/types.h"
#include "src/dec/vp8i_dec.h"
#include "src/dec/webpi_dec.h"
#include "src/dsp/cpu.h"
#include "src/dsp/dsp.h"
#include "src/dsp/yuv.h"
#include "src/utils/rescaler_utils.h"
#include "src/utils/utils.h"
#include "src/webp/decode.h"

//------------------------------------------------------------------------------
// Main YUV<->RGB conversion functions

static int EmitYUV(const VP8Io* const io, WebPDecParams* const p) {
 WebPDecBuffer* output = p->output;
 const WebPYUVABuffer* const buf = &output->u.YUVA;
 uint8_t* const y_dst = buf->y + (ptrdiff_t)io->mb_y * buf->y_stride;
 uint8_t* const u_dst = buf->u + (ptrdiff_t)(io->mb_y >> 1) * buf->u_stride;
 uint8_t* const v_dst = buf->v + (ptrdiff_t)(io->mb_y >> 1) * buf->v_stride;
 const int mb_w = io->mb_w;
 const int mb_h = io->mb_h;
 const int uv_w = (mb_w + 1) / 2;
 const int uv_h = (mb_h + 1) / 2;
 WebPCopyPlane(io->y, io->y_stride, y_dst, buf->y_stride, mb_w, mb_h);
 WebPCopyPlane(io->u, io->uv_stride, u_dst, buf->u_stride, uv_w, uv_h);
 WebPCopyPlane(io->v, io->uv_stride, v_dst, buf->v_stride, uv_w, uv_h);
 return io->mb_h;
}

// Point-sampling U/V sampler.
static int EmitSampledRGB(const VP8Io* const io, WebPDecParams* const p) {
 WebPDecBuffer* const output = p->output;
 WebPRGBABuffer* const buf = &output->u.RGBA;
 uint8_t* const dst = buf->rgba + (ptrdiff_t)io->mb_y * buf->stride;
 WebPSamplerProcessPlane(io->y, io->y_stride,
                         io->u, io->v, io->uv_stride,
                         dst, buf->stride, io->mb_w, io->mb_h,
                         WebPSamplers[output->colorspace]);
 return io->mb_h;
}

//------------------------------------------------------------------------------
// Fancy upsampling

#ifdef FANCY_UPSAMPLING
static int EmitFancyRGB(const VP8Io* const io, WebPDecParams* const p) {
 int num_lines_out = io->mb_h;   // a priori guess
 const WebPRGBABuffer* const buf = &p->output->u.RGBA;
 uint8_t* dst = buf->rgba + (ptrdiff_t)io->mb_y * buf->stride;
 WebPUpsampleLinePairFunc upsample = WebPUpsamplers[p->output->colorspace];
 const uint8_t* cur_y = io->y;
 const uint8_t* cur_u = io->u;
 const uint8_t* cur_v = io->v;
 const uint8_t* top_u = p->tmp_u;
 const uint8_t* top_v = p->tmp_v;
 int y = io->mb_y;
 const int y_end = io->mb_y + io->mb_h;
 const int mb_w = io->mb_w;
 const int uv_w = (mb_w + 1) / 2;

 if (y == 0) {
   // First line is special cased. We mirror the u/v samples at boundary.
   upsample(cur_y, NULL, cur_u, cur_v, cur_u, cur_v, dst, NULL, mb_w);
 } else {
   // We can finish the left-over line from previous call.
   upsample(p->tmp_y, cur_y, top_u, top_v, cur_u, cur_v,
            dst - buf->stride, dst, mb_w);
   ++num_lines_out;
 }
 // Loop over each output pairs of row.
 for (; y + 2 < y_end; y += 2) {
   top_u = cur_u;
   top_v = cur_v;
   cur_u += io->uv_stride;
   cur_v += io->uv_stride;
   dst += 2 * buf->stride;
   cur_y += 2 * io->y_stride;
   upsample(cur_y - io->y_stride, cur_y,
            top_u, top_v, cur_u, cur_v,
            dst - buf->stride, dst, mb_w);
 }
 // move to last row
 cur_y += io->y_stride;
 if (io->crop_top + y_end < io->crop_bottom) {
   // Save the unfinished samples for next call (as we're not done yet).
   memcpy(p->tmp_y, cur_y, mb_w * sizeof(*p->tmp_y));
   memcpy(p->tmp_u, cur_u, uv_w * sizeof(*p->tmp_u));
   memcpy(p->tmp_v, cur_v, uv_w * sizeof(*p->tmp_v));
   // The fancy upsampler leaves a row unfinished behind
   // (except for the very last row)
   num_lines_out--;
 } else {
   // Process the very last row of even-sized picture
   if (!(y_end & 1)) {
     upsample(cur_y, NULL, cur_u, cur_v, cur_u, cur_v,
              dst + buf->stride, NULL, mb_w);
   }
 }
 return num_lines_out;
}

#endif    /* FANCY_UPSAMPLING */

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

static void FillAlphaPlane(uint8_t* dst, int w, int h, int stride) {
 int j;
 for (j = 0; j < h; ++j) {
   memset(dst, 0xff, w * sizeof(*dst));
   dst += stride;
 }
}

static int EmitAlphaYUV(const VP8Io* const io, WebPDecParams* const p,
                       int expected_num_lines_out) {
 const uint8_t* alpha = io->a;
 const WebPYUVABuffer* const buf = &p->output->u.YUVA;
 const int mb_w = io->mb_w;
 const int mb_h = io->mb_h;
 uint8_t* dst = buf->a + (ptrdiff_t)io->mb_y * buf->a_stride;
 int j;
 (void)expected_num_lines_out;
 assert(expected_num_lines_out == mb_h);
 if (alpha != NULL) {
   for (j = 0; j < mb_h; ++j) {
     memcpy(dst, alpha, mb_w * sizeof(*dst));
     alpha += io->width;
     dst += buf->a_stride;
   }
 } else if (buf->a != NULL) {
   // the user requested alpha, but there is none, set it to opaque.
   FillAlphaPlane(dst, mb_w, mb_h, buf->a_stride);
 }
 return 0;
}

static int GetAlphaSourceRow(const VP8Io* const io,
                            const uint8_t** alpha, int* const num_rows) {
 int start_y = io->mb_y;
 *num_rows = io->mb_h;

 // Compensate for the 1-line delay of the fancy upscaler.
 // This is similar to EmitFancyRGB().
 if (io->fancy_upsampling) {
   if (start_y == 0) {
     // We don't process the last row yet. It'll be done during the next call.
     --*num_rows;
   } else {
     --start_y;
     // Fortunately, *alpha data is persistent, so we can go back
     // one row and finish alpha blending, now that the fancy upscaler
     // completed the YUV->RGB interpolation.
     *alpha -= io->width;
   }
   if (io->crop_top + io->mb_y + io->mb_h == io->crop_bottom) {
     // If it's the very last call, we process all the remaining rows!
     *num_rows = io->crop_bottom - io->crop_top - start_y;
   }
 }
 return start_y;
}

static int EmitAlphaRGB(const VP8Io* const io, WebPDecParams* const p,
                       int expected_num_lines_out) {
 const uint8_t* alpha = io->a;
 if (alpha != NULL) {
   const int mb_w = io->mb_w;
   const WEBP_CSP_MODE colorspace = p->output->colorspace;
   const int alpha_first =
       (colorspace == MODE_ARGB || colorspace == MODE_Argb);
   const WebPRGBABuffer* const buf = &p->output->u.RGBA;
   int num_rows;
   const int start_y = GetAlphaSourceRow(io, &alpha, &num_rows);
   uint8_t* const base_rgba = buf->rgba + (ptrdiff_t)start_y * buf->stride;
   uint8_t* const dst = base_rgba + (alpha_first ? 0 : 3);
   const int has_alpha = WebPDispatchAlpha(alpha, io->width, mb_w,
                                           num_rows, dst, buf->stride);
   (void)expected_num_lines_out;
   assert(expected_num_lines_out == num_rows);
   // has_alpha is true if there's non-trivial alpha to premultiply with.
   if (has_alpha && WebPIsPremultipliedMode(colorspace)) {
     WebPApplyAlphaMultiply(base_rgba, alpha_first,
                            mb_w, num_rows, buf->stride);
   }
 }
 return 0;
}

static int EmitAlphaRGBA4444(const VP8Io* const io, WebPDecParams* const p,
                            int expected_num_lines_out) {
 const uint8_t* alpha = io->a;
 if (alpha != NULL) {
   const int mb_w = io->mb_w;
   const WEBP_CSP_MODE colorspace = p->output->colorspace;
   const WebPRGBABuffer* const buf = &p->output->u.RGBA;
   int num_rows;
   const int start_y = GetAlphaSourceRow(io, &alpha, &num_rows);
   uint8_t* const base_rgba = buf->rgba + (ptrdiff_t)start_y * buf->stride;
#if (WEBP_SWAP_16BIT_CSP == 1)
   uint8_t* alpha_dst = base_rgba;
#else
   uint8_t* alpha_dst = base_rgba + 1;
#endif
   uint32_t alpha_mask = 0x0f;
   int i, j;
   for (j = 0; j < num_rows; ++j) {
     for (i = 0; i < mb_w; ++i) {
       // Fill in the alpha value (converted to 4 bits).
       const uint32_t alpha_value = alpha[i] >> 4;
       alpha_dst[2 * i] = (alpha_dst[2 * i] & 0xf0) | alpha_value;
       alpha_mask &= alpha_value;
     }
     alpha += io->width;
     alpha_dst += buf->stride;
   }
   (void)expected_num_lines_out;
   assert(expected_num_lines_out == num_rows);
   if (alpha_mask != 0x0f && WebPIsPremultipliedMode(colorspace)) {
     WebPApplyAlphaMultiply4444(base_rgba, mb_w, num_rows, buf->stride);
   }
 }
 return 0;
}

//------------------------------------------------------------------------------
// YUV rescaling (no final RGB conversion needed)

#if !defined(WEBP_REDUCE_SIZE)
static int Rescale(const uint8_t* src, int src_stride,
                  int new_lines, WebPRescaler* const wrk) {
 int num_lines_out = 0;
 while (new_lines > 0) {    // import new contributions of source rows.
   const int lines_in = WebPRescalerImport(wrk, new_lines, src, src_stride);
   src += lines_in * src_stride;
   new_lines -= lines_in;
   num_lines_out += WebPRescalerExport(wrk);    // emit output row(s)
 }
 return num_lines_out;
}

static int EmitRescaledYUV(const VP8Io* const io, WebPDecParams* const p) {
 const int mb_h = io->mb_h;
 const int uv_mb_h = (mb_h + 1) >> 1;
 WebPRescaler* const scaler = p->scaler_y;
 int num_lines_out = 0;
 if (WebPIsAlphaMode(p->output->colorspace) && io->a != NULL) {
   // Before rescaling, we premultiply the luma directly into the io->y
   // internal buffer. This is OK since these samples are not used for
   // intra-prediction (the top samples are saved in cache_y/u/v).
   // But we need to cast the const away, though.
   WebPMultRows((uint8_t*)io->y, io->y_stride,
                io->a, io->width, io->mb_w, mb_h, 0);
 }
 num_lines_out = Rescale(io->y, io->y_stride, mb_h, scaler);
 Rescale(io->u, io->uv_stride, uv_mb_h, p->scaler_u);
 Rescale(io->v, io->uv_stride, uv_mb_h, p->scaler_v);
 return num_lines_out;
}

static int EmitRescaledAlphaYUV(const VP8Io* const io, WebPDecParams* const p,
                               int expected_num_lines_out) {
 const WebPYUVABuffer* const buf = &p->output->u.YUVA;
 uint8_t* const dst_a = buf->a + (ptrdiff_t)p->last_y * buf->a_stride;
 if (io->a != NULL) {
   uint8_t* const dst_y = buf->y + (ptrdiff_t)p->last_y * buf->y_stride;
   const int num_lines_out = Rescale(io->a, io->width, io->mb_h, p->scaler_a);
   assert(expected_num_lines_out == num_lines_out);
   if (num_lines_out > 0) {   // unmultiply the Y
     WebPMultRows(dst_y, buf->y_stride, dst_a, buf->a_stride,
                  p->scaler_a->dst_width, num_lines_out, 1);
   }
 } else if (buf->a != NULL) {
   // the user requested alpha, but there is none, set it to opaque.
   assert(p->last_y + expected_num_lines_out <= io->scaled_height);
   FillAlphaPlane(dst_a, io->scaled_width, expected_num_lines_out,
                  buf->a_stride);
 }
 return 0;
}

static int InitYUVRescaler(const VP8Io* const io, WebPDecParams* const p) {
 const int has_alpha = WebPIsAlphaMode(p->output->colorspace);
 const WebPYUVABuffer* const buf = &p->output->u.YUVA;
 const int out_width  = io->scaled_width;
 const int out_height = io->scaled_height;
 const int uv_out_width  = (out_width + 1) >> 1;
 const int uv_out_height = (out_height + 1) >> 1;
 const int uv_in_width  = (io->mb_w + 1) >> 1;
 const int uv_in_height = (io->mb_h + 1) >> 1;
 // scratch memory for luma rescaler
 const size_t work_size = 2 * (size_t)out_width;
 const size_t uv_work_size = 2 * uv_out_width;  // and for each u/v ones
 uint64_t total_size;
 size_t rescaler_size;
 rescaler_t* work;
 WebPRescaler* scalers;
 const int num_rescalers = has_alpha ? 4 : 3;

 total_size = ((uint64_t)work_size + 2 * uv_work_size) * sizeof(*work);
 if (has_alpha) {
   total_size += (uint64_t)work_size * sizeof(*work);
 }
 rescaler_size = num_rescalers * sizeof(*p->scaler_y) + WEBP_ALIGN_CST;
 total_size += rescaler_size;
 if (!CheckSizeOverflow(total_size)) {
   return 0;
 }

 p->memory = WebPSafeMalloc(1ULL, (size_t)total_size);
 if (p->memory == NULL) {
   return 0;   // memory error
 }
 work = (rescaler_t*)p->memory;

 scalers = (WebPRescaler*)WEBP_ALIGN(
     (const uint8_t*)work + total_size - rescaler_size);
 p->scaler_y = &scalers[0];
 p->scaler_u = &scalers[1];
 p->scaler_v = &scalers[2];
 p->scaler_a = has_alpha ? &scalers[3] : NULL;

 if (!WebPRescalerInit(p->scaler_y, io->mb_w, io->mb_h,
                       buf->y, out_width, out_height, buf->y_stride, 1,
                       work) ||
     !WebPRescalerInit(p->scaler_u, uv_in_width, uv_in_height,
                       buf->u, uv_out_width, uv_out_height, buf->u_stride, 1,
                       work + work_size) ||
     !WebPRescalerInit(p->scaler_v, uv_in_width, uv_in_height,
                       buf->v, uv_out_width, uv_out_height, buf->v_stride, 1,
                       work + work_size + uv_work_size)) {
   return 0;
 }
 p->emit = EmitRescaledYUV;

 if (has_alpha) {
   if (!WebPRescalerInit(p->scaler_a, io->mb_w, io->mb_h,
                         buf->a, out_width, out_height, buf->a_stride, 1,
                         work + work_size + 2 * uv_work_size)) {
     return 0;
   }
   p->emit_alpha = EmitRescaledAlphaYUV;
   WebPInitAlphaProcessing();
 }
 return 1;
}

//------------------------------------------------------------------------------
// RGBA rescaling

static int ExportRGB(WebPDecParams* const p, int y_pos) {
 const WebPYUV444Converter convert =
     WebPYUV444Converters[p->output->colorspace];
 const WebPRGBABuffer* const buf = &p->output->u.RGBA;
 uint8_t* dst = buf->rgba + (ptrdiff_t)y_pos * buf->stride;
 int num_lines_out = 0;
 // For RGB rescaling, because of the YUV420, current scan position
 // U/V can be +1/-1 line from the Y one.  Hence the double test.
 while (WebPRescalerHasPendingOutput(p->scaler_y) &&
        WebPRescalerHasPendingOutput(p->scaler_u)) {
   assert(y_pos + num_lines_out < p->output->height);
   assert(p->scaler_u->y_accum == p->scaler_v->y_accum);
   WebPRescalerExportRow(p->scaler_y);
   WebPRescalerExportRow(p->scaler_u);
   WebPRescalerExportRow(p->scaler_v);
   convert(p->scaler_y->dst, p->scaler_u->dst, p->scaler_v->dst,
           dst, p->scaler_y->dst_width);
   dst += buf->stride;
   ++num_lines_out;
 }
 return num_lines_out;
}

static int EmitRescaledRGB(const VP8Io* const io, WebPDecParams* const p) {
 const int mb_h = io->mb_h;
 const int uv_mb_h = (mb_h + 1) >> 1;
 int j = 0, uv_j = 0;
 int num_lines_out = 0;
 while (j < mb_h) {
   const int y_lines_in =
       WebPRescalerImport(p->scaler_y, mb_h - j,
                          io->y + (ptrdiff_t)j * io->y_stride, io->y_stride);
   j += y_lines_in;
   if (WebPRescaleNeededLines(p->scaler_u, uv_mb_h - uv_j)) {
     const int u_lines_in = WebPRescalerImport(
         p->scaler_u, uv_mb_h - uv_j, io->u + (ptrdiff_t)uv_j * io->uv_stride,
         io->uv_stride);
     const int v_lines_in = WebPRescalerImport(
         p->scaler_v, uv_mb_h - uv_j, io->v + (ptrdiff_t)uv_j * io->uv_stride,
         io->uv_stride);
     (void)v_lines_in;   // remove a gcc warning
     assert(u_lines_in == v_lines_in);
     uv_j += u_lines_in;
   }
   num_lines_out += ExportRGB(p, p->last_y + num_lines_out);
 }
 return num_lines_out;
}

static int ExportAlpha(WebPDecParams* const p, int y_pos, int max_lines_out) {
 const WebPRGBABuffer* const buf = &p->output->u.RGBA;
 uint8_t* const base_rgba = buf->rgba + (ptrdiff_t)y_pos * buf->stride;
 const WEBP_CSP_MODE colorspace = p->output->colorspace;
 const int alpha_first =
     (colorspace == MODE_ARGB || colorspace == MODE_Argb);
 uint8_t* dst = base_rgba + (alpha_first ? 0 : 3);
 int num_lines_out = 0;
 const int is_premult_alpha = WebPIsPremultipliedMode(colorspace);
 uint32_t non_opaque = 0;
 const int width = p->scaler_a->dst_width;

 while (WebPRescalerHasPendingOutput(p->scaler_a) &&
        num_lines_out < max_lines_out) {
   assert(y_pos + num_lines_out < p->output->height);
   WebPRescalerExportRow(p->scaler_a);
   non_opaque |= WebPDispatchAlpha(p->scaler_a->dst, 0, width, 1, dst, 0);
   dst += buf->stride;
   ++num_lines_out;
 }
 if (is_premult_alpha && non_opaque) {
   WebPApplyAlphaMultiply(base_rgba, alpha_first,
                          width, num_lines_out, buf->stride);
 }
 return num_lines_out;
}

static int ExportAlphaRGBA4444(WebPDecParams* const p, int y_pos,
                              int max_lines_out) {
 const WebPRGBABuffer* const buf = &p->output->u.RGBA;
 uint8_t* const base_rgba = buf->rgba + (ptrdiff_t)y_pos * buf->stride;
#if (WEBP_SWAP_16BIT_CSP == 1)
 uint8_t* alpha_dst = base_rgba;
#else
 uint8_t* alpha_dst = base_rgba + 1;
#endif
 int num_lines_out = 0;
 const WEBP_CSP_MODE colorspace = p->output->colorspace;
 const int width = p->scaler_a->dst_width;
 const int is_premult_alpha = WebPIsPremultipliedMode(colorspace);
 uint32_t alpha_mask = 0x0f;

 while (WebPRescalerHasPendingOutput(p->scaler_a) &&
        num_lines_out < max_lines_out) {
   int i;
   assert(y_pos + num_lines_out < p->output->height);
   WebPRescalerExportRow(p->scaler_a);
   for (i = 0; i < width; ++i) {
     // Fill in the alpha value (converted to 4 bits).
     const uint32_t alpha_value = p->scaler_a->dst[i] >> 4;
     alpha_dst[2 * i] = (alpha_dst[2 * i] & 0xf0) | alpha_value;
     alpha_mask &= alpha_value;
   }
   alpha_dst += buf->stride;
   ++num_lines_out;
 }
 if (is_premult_alpha && alpha_mask != 0x0f) {
   WebPApplyAlphaMultiply4444(base_rgba, width, num_lines_out, buf->stride);
 }
 return num_lines_out;
}

static int EmitRescaledAlphaRGB(const VP8Io* const io, WebPDecParams* const p,
                               int expected_num_out_lines) {
 if (io->a != NULL) {
   WebPRescaler* const scaler = p->scaler_a;
   int lines_left = expected_num_out_lines;
   const int y_end = p->last_y + lines_left;
   while (lines_left > 0) {
     const int64_t row_offset = (ptrdiff_t)scaler->src_y - io->mb_y;
     WebPRescalerImport(scaler, io->mb_h + io->mb_y - scaler->src_y,
                        io->a + row_offset * io->width, io->width);
     lines_left -= p->emit_alpha_row(p, y_end - lines_left, lines_left);
   }
 }
 return 0;
}

static int InitRGBRescaler(const VP8Io* const io, WebPDecParams* const p) {
 const int has_alpha = WebPIsAlphaMode(p->output->colorspace);
 const int out_width  = io->scaled_width;
 const int out_height = io->scaled_height;
 const int uv_in_width  = (io->mb_w + 1) >> 1;
 const int uv_in_height = (io->mb_h + 1) >> 1;
 // scratch memory for one rescaler
 const size_t work_size = 2 * (size_t)out_width;
 rescaler_t* work;  // rescalers work area
 uint8_t* tmp;   // tmp storage for scaled YUV444 samples before RGB conversion
 uint64_t tmp_size1, tmp_size2, total_size;
 size_t rescaler_size;
 WebPRescaler* scalers;
 const int num_rescalers = has_alpha ? 4 : 3;

 tmp_size1 = (uint64_t)num_rescalers * work_size;
 tmp_size2 = (uint64_t)num_rescalers * out_width;
 total_size = tmp_size1 * sizeof(*work) + tmp_size2 * sizeof(*tmp);
 rescaler_size = num_rescalers * sizeof(*p->scaler_y) + WEBP_ALIGN_CST;
 total_size += rescaler_size;
 if (!CheckSizeOverflow(total_size)) {
   return 0;
 }

 p->memory = WebPSafeMalloc(1ULL, (size_t)total_size);
 if (p->memory == NULL) {
   return 0;   // memory error
 }
 work = (rescaler_t*)p->memory;
 tmp = (uint8_t*)(work + tmp_size1);

 scalers = (WebPRescaler*)WEBP_ALIGN(
     (const uint8_t*)work + total_size - rescaler_size);
 p->scaler_y = &scalers[0];
 p->scaler_u = &scalers[1];
 p->scaler_v = &scalers[2];
 p->scaler_a = has_alpha ? &scalers[3] : NULL;

 if (!WebPRescalerInit(p->scaler_y, io->mb_w, io->mb_h,
                       tmp + 0 * out_width, out_width, out_height, 0, 1,
                       work + 0 * work_size) ||
     !WebPRescalerInit(p->scaler_u, uv_in_width, uv_in_height,
                       tmp + 1 * out_width, out_width, out_height, 0, 1,
                       work + 1 * work_size) ||
     !WebPRescalerInit(p->scaler_v, uv_in_width, uv_in_height,
                       tmp + 2 * out_width, out_width, out_height, 0, 1,
                       work + 2 * work_size)) {
   return 0;
 }
 p->emit = EmitRescaledRGB;
 WebPInitYUV444Converters();

 if (has_alpha) {
   if (!WebPRescalerInit(p->scaler_a, io->mb_w, io->mb_h,
                         tmp + 3 * out_width, out_width, out_height, 0, 1,
                         work + 3 * work_size)) {
     return 0;
   }
   p->emit_alpha = EmitRescaledAlphaRGB;
   if (p->output->colorspace == MODE_RGBA_4444 ||
       p->output->colorspace == MODE_rgbA_4444) {
     p->emit_alpha_row = ExportAlphaRGBA4444;
   } else {
     p->emit_alpha_row = ExportAlpha;
   }
   WebPInitAlphaProcessing();
 }
 return 1;
}

#endif  // WEBP_REDUCE_SIZE

//------------------------------------------------------------------------------
// Default custom functions

static int CustomSetup(VP8Io* io) {
 WebPDecParams* const p = (WebPDecParams*)io->opaque;
 const WEBP_CSP_MODE colorspace = p->output->colorspace;
 const int is_rgb = WebPIsRGBMode(colorspace);
 const int is_alpha = WebPIsAlphaMode(colorspace);

 p->memory = NULL;
 p->emit = NULL;
 p->emit_alpha = NULL;
 p->emit_alpha_row = NULL;
 if (!WebPIoInitFromOptions(p->options, io, is_alpha ? MODE_YUV : MODE_YUVA)) {
   return 0;
 }
 if (is_alpha && WebPIsPremultipliedMode(colorspace)) {
   WebPInitUpsamplers();
 }
 if (io->use_scaling) {
#if !defined(WEBP_REDUCE_SIZE)
   const int ok = is_rgb ? InitRGBRescaler(io, p) : InitYUVRescaler(io, p);
   if (!ok) {
     return 0;    // memory error
   }
#else
   return 0;   // rescaling support not compiled
#endif
 } else {
   if (is_rgb) {
     WebPInitSamplers();
     p->emit = EmitSampledRGB;   // default
     if (io->fancy_upsampling) {
#ifdef FANCY_UPSAMPLING
       const int uv_width = (io->mb_w + 1) >> 1;
       p->memory = WebPSafeMalloc(1ULL, (size_t)(io->mb_w + 2 * uv_width));
       if (p->memory == NULL) {
         return 0;   // memory error.
       }
       p->tmp_y = (uint8_t*)p->memory;
       p->tmp_u = p->tmp_y + io->mb_w;
       p->tmp_v = p->tmp_u + uv_width;
       p->emit = EmitFancyRGB;
       WebPInitUpsamplers();
#endif
     }
   } else {
     p->emit = EmitYUV;
   }
   if (is_alpha) {  // need transparency output
     p->emit_alpha =
         (colorspace == MODE_RGBA_4444 || colorspace == MODE_rgbA_4444) ?
             EmitAlphaRGBA4444
         : is_rgb ? EmitAlphaRGB
         : EmitAlphaYUV;
     if (is_rgb) {
       WebPInitAlphaProcessing();
     }
   }
 }

 return 1;
}

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

static int CustomPut(const VP8Io* io) {
 WebPDecParams* const p = (WebPDecParams*)io->opaque;
 const int mb_w = io->mb_w;
 const int mb_h = io->mb_h;
 int num_lines_out;
 assert(!(io->mb_y & 1));

 if (mb_w <= 0 || mb_h <= 0) {
   return 0;
 }
 num_lines_out = p->emit(io, p);
 if (p->emit_alpha != NULL) {
   p->emit_alpha(io, p, num_lines_out);
 }
 p->last_y += num_lines_out;
 return 1;
}

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

static void CustomTeardown(const VP8Io* io) {
 WebPDecParams* const p = (WebPDecParams*)io->opaque;
 WebPSafeFree(p->memory);
 p->memory = NULL;
}

//------------------------------------------------------------------------------
// Main entry point

void WebPInitCustomIo(WebPDecParams* const params, VP8Io* const io) {
 io->put      = CustomPut;
 io->setup    = CustomSetup;
 io->teardown = CustomTeardown;
 io->opaque   = params;
}

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