Use the upstream version of libwebp, v0.4.3.

third_party/libwebp/dec/io.c

+// 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 <stdlib.h>
+#include "../dec/vp8i.h"
+#include "./webpi.h"
+#include "../dsp/dsp.h"
+#include "../dsp/yuv.h"
+#include "../utils/utils.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 + io->mb_y * buf->y_stride;
+  uint8_t* const u_dst = buf->u + (io->mb_y >> 1) * buf->u_stride;
+  uint8_t* const v_dst = buf->v + (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;
+  int j;
+  for (j = 0; j < mb_h; ++j) {
+    memcpy(y_dst + j * buf->y_stride, io->y + j * io->y_stride, mb_w);
+  }
+  for (j = 0; j < uv_h; ++j) {
+    memcpy(u_dst + j * buf->u_stride, io->u + j * io->uv_stride, uv_w);
+    memcpy(v_dst + j * buf->v_stride, io->v + j * io->uv_stride, uv_w);
+  }
+  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 + 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;
+}
+
+//------------------------------------------------------------------------------
+// YUV444 -> RGB conversion
+
+#if 0   // TODO(skal): this is for future rescaling.
+static int EmitRGB(const VP8Io* const io, WebPDecParams* const p) {
+  WebPDecBuffer* output = p->output;
+  const WebPRGBABuffer* const buf = &output->u.RGBA;
+  uint8_t* dst = buf->rgba + io->mb_y * buf->stride;
+  const uint8_t* y_src = io->y;
+  const uint8_t* u_src = io->u;
+  const uint8_t* v_src = io->v;
+  const WebPYUV444Converter convert = WebPYUV444Converters[output->colorspace];
+  const int mb_w = io->mb_w;
+  const int last = io->mb_h;
+  int j;
+  for (j = 0; j < last; ++j) {
+    convert(y_src, u_src, v_src, dst, mb_w);
+    y_src += io->y_stride;
+    u_src += io->uv_stride;
+    v_src += io->uv_stride;
+    dst += buf->stride;
+  }
+  return io->mb_h;
+}
+#endif
+
+//------------------------------------------------------------------------------
+// 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 + 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 int EmitAlphaYUV(const VP8Io* const io, WebPDecParams* const p) {
+  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 + io->mb_y * buf->a_stride;
+  int j;
+
+  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.
+    for (j = 0; j < mb_h; ++j) {
+      memset(dst, 0xff, mb_w * sizeof(*dst));
+      dst += 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) {
+  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 + start_y * buf->stride;
+    uint8_t* dst = base_rgba + (alpha_first ? 0 : 3);
+    uint32_t alpha_mask = 0xff;
+    int i, j;
+
+    for (j = 0; j < num_rows; ++j) {
+      for (i = 0; i < mb_w; ++i) {
+        const uint32_t alpha_value = alpha[i];
+        dst[4 * i] = alpha_value;
+        alpha_mask &= alpha_value;
+      }
+      alpha += io->width;
+      dst += buf->stride;
+    }
+    // alpha_mask is < 0xff if there's non-trivial alpha to premultiply with.
+    if (alpha_mask != 0xff && 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) {
+  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 + start_y * buf->stride;
+#ifdef WEBP_SWAP_16BIT_CSP
+    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;
+    }
+    if (alpha_mask != 0x0f && WebPIsPremultipliedMode(colorspace)) {
+      WebPApplyAlphaMultiply4444(base_rgba, mb_w, num_rows, buf->stride);
+    }
+  }
+  return 0;
+}
+
+//------------------------------------------------------------------------------
+// YUV rescaling (no final RGB conversion needed)
+
+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) {
+  if (io->a != NULL) {
+    const WebPYUVABuffer* const buf = &p->output->u.YUVA;
+    uint8_t* dst_y = buf->y + p->last_y * buf->y_stride;
+    const uint8_t* src_a = buf->a + p->last_y * buf->a_stride;
+    const int num_lines_out = Rescale(io->a, io->width, io->mb_h, &p->scaler_a);
+    if (num_lines_out > 0) {   // unmultiply the Y
+      WebPMultRows(dst_y, buf->y_stride, src_a, buf->a_stride,
+                   p->scaler_a.dst_width, num_lines_out, 1);
+    }
+  }
+  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;
+  const size_t work_size = 2 * out_width;   // scratch memory for luma rescaler
+  const size_t uv_work_size = 2 * uv_out_width;  // and for each u/v ones
+  size_t tmp_size;
+  int32_t* work;
+
+  tmp_size = (work_size + 2 * uv_work_size) * sizeof(*work);
+  if (has_alpha) {
+    tmp_size += work_size * sizeof(*work);
+  }
+  p->memory = WebPSafeCalloc(1ULL, tmp_size);
+  if (p->memory == NULL) {
+    return 0;   // memory error
+  }
+  work = (int32_t*)p->memory;
+  WebPRescalerInit(&p->scaler_y, io->mb_w, io->mb_h,
+                   buf->y, out_width, out_height, buf->y_stride, 1,
+                   io->mb_w, out_width, io->mb_h, out_height,
+                   work);
+  WebPRescalerInit(&p->scaler_u, uv_in_width, uv_in_height,
+                   buf->u, uv_out_width, uv_out_height, buf->u_stride, 1,
+                   uv_in_width, uv_out_width,
+                   uv_in_height, uv_out_height,
+                   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,
+                   uv_in_width, uv_out_width,
+                   uv_in_height, uv_out_height,
+                   work + work_size + uv_work_size);
+  p->emit = EmitRescaledYUV;
+
+  if (has_alpha) {
+    WebPRescalerInit(&p->scaler_a, io->mb_w, io->mb_h,
+                     buf->a, out_width, out_height, buf->a_stride, 1,
+                     io->mb_w, out_width, io->mb_h, out_height,
+                     work + work_size + 2 * uv_work_size);
+    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 + (p->last_y + 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(p->last_y + y_pos + num_lines_out < p->output->height);
+    assert(p->scaler_u.y_accum == p->scaler_v.y_accum);
+    WebPRescalerExportRow(&p->scaler_y, 0);
+    WebPRescalerExportRow(&p->scaler_u, 0);
+    WebPRescalerExportRow(&p->scaler_v, 0);
+    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 + j * io->y_stride, io->y_stride);
+    const int u_lines_in =
+        WebPRescalerImport(&p->scaler_u, uv_mb_h - uv_j,
+                           io->u + uv_j * io->uv_stride, io->uv_stride);
+    const int v_lines_in =
+        WebPRescalerImport(&p->scaler_v, uv_mb_h - uv_j,
+                           io->v + uv_j * io->uv_stride, io->uv_stride);
+    (void)v_lines_in;   // remove a gcc warning
+    assert(u_lines_in == v_lines_in);
+    j += y_lines_in;
+    uv_j += u_lines_in;
+    num_lines_out += ExportRGB(p, num_lines_out);
+  }
+  return num_lines_out;
+}
+
+static int ExportAlpha(WebPDecParams* const p, int y_pos) {
+  const WebPRGBABuffer* const buf = &p->output->u.RGBA;
+  uint8_t* const base_rgba = buf->rgba + (p->last_y + 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 alpha_mask = 0xff;
+  const int width = p->scaler_a.dst_width;
+
+  while (WebPRescalerHasPendingOutput(&p->scaler_a)) {
+    int i;
+    assert(p->last_y + y_pos + num_lines_out < p->output->height);
+    WebPRescalerExportRow(&p->scaler_a, 0);
+    for (i = 0; i < width; ++i) {
+      const uint32_t alpha_value = p->scaler_a.dst[i];
+      dst[4 * i] = alpha_value;
+      alpha_mask &= alpha_value;
+    }
+    dst += buf->stride;
+    ++num_lines_out;
+  }
+  if (is_premult_alpha && alpha_mask != 0xff) {
+    WebPApplyAlphaMultiply(base_rgba, alpha_first,
+                           width, num_lines_out, buf->stride);
+  }
+  return num_lines_out;
+}
+
+static int ExportAlphaRGBA4444(WebPDecParams* const p, int y_pos) {
+  const WebPRGBABuffer* const buf = &p->output->u.RGBA;
+  uint8_t* const base_rgba = buf->rgba + (p->last_y + y_pos) * buf->stride;
+#ifdef WEBP_SWAP_16BIT_CSP
+  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)) {
+    int i;
+    assert(p->last_y + y_pos + num_lines_out < p->output->height);
+    WebPRescalerExportRow(&p->scaler_a, 0);
+    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) {
+  if (io->a != NULL) {
+    WebPRescaler* const scaler = &p->scaler_a;
+    int j = 0;
+    int pos = 0;
+    while (j < io->mb_h) {
+      j += WebPRescalerImport(scaler, io->mb_h - j,
+                              io->a + j * io->width, io->width);
+      pos += p->emit_alpha_row(p, pos);
+    }
+  }
+  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;
+  const size_t work_size = 2 * out_width;   // scratch memory for one rescaler
+  int32_t* work;  // rescalers work area
+  uint8_t* tmp;   // tmp storage for scaled YUV444 samples before RGB conversion
+  size_t tmp_size1, tmp_size2, total_size;
+
+  tmp_size1 = 3 * work_size;
+  tmp_size2 = 3 * out_width;
+  if (has_alpha) {
+    tmp_size1 += work_size;
+    tmp_size2 += out_width;
+  }
+  total_size = tmp_size1 * sizeof(*work) + tmp_size2 * sizeof(*tmp);
+  p->memory = WebPSafeCalloc(1ULL, total_size);
+  if (p->memory == NULL) {
+    return 0;   // memory error
+  }
+  work = (int32_t*)p->memory;
+  tmp = (uint8_t*)(work + tmp_size1);
+  WebPRescalerInit(&p->scaler_y, io->mb_w, io->mb_h,
+                   tmp + 0 * out_width, out_width, out_height, 0, 1,
+                   io->mb_w, out_width, io->mb_h, out_height,
+                   work + 0 * work_size);
+  WebPRescalerInit(&p->scaler_u, uv_in_width, uv_in_height,
+                   tmp + 1 * out_width, out_width, out_height, 0, 1,
+                   io->mb_w, 2 * out_width, io->mb_h, 2 * out_height,
+                   work + 1 * work_size);
+  WebPRescalerInit(&p->scaler_v, uv_in_width, uv_in_height,
+                   tmp + 2 * out_width, out_width, out_height, 0, 1,
+                   io->mb_w, 2 * out_width, io->mb_h, 2 * out_height,
+                   work + 2 * work_size);
+  p->emit = EmitRescaledRGB;
+
+  if (has_alpha) {
+    WebPRescalerInit(&p->scaler_a, io->mb_w, io->mb_h,
+                     tmp + 3 * out_width, out_width, out_height, 0, 1,
+                     io->mb_w, out_width, io->mb_h, out_height,
+                     work + 3 * work_size);
+    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;
+}
+
+//------------------------------------------------------------------------------
+// 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) {
+    const int ok = is_rgb ? InitRGBRescaler(io, p) : InitYUVRescaler(io, p);
+    if (!ok) {
+      return 0;    // memory error
+    }
+  } else {
+    if (is_rgb) {
+      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 {
+        WebPInitSamplers();
+      }
+    } 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();
+      }
+    }
+  }
+
+  if (is_rgb) {
+    VP8YUVInit();
+  }
+  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);
+  }
+  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;
+}
+
+//------------------------------------------------------------------------------