blimp/common/compositor/webp_decoder.cc

// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "blimp/common/compositor/webp_decoder.h"

#include "base/logging.h"
#include "third_party/libwebp/webp/decode.h"
#include "third_party/libwebp/webp/demux.h"
#include "third_party/skia/include/core/SkBitmap.h"

namespace blimp {

bool WebPDecoder(const void* input, size_t input_size, SkBitmap* bitmap) {
  DCHECK(bitmap);

  // Initialize an empty WebPDecoderConfig.
  WebPDecoderConfig config;
  if (!WebPInitDecoderConfig(&config)) {
    LOG(WARNING) << "Failed to initialize WebP config.";
    return false;
  }

  // Treat the input as uint8_t.
  WebPData data = {reinterpret_cast<const uint8_t*>(input), input_size};

  // Read WebP feature information into |config.input|, which is a
  // WebPBitstreamFeatures. It contains information such as width, height and
  // whether the WebP image has an alpha channel or not.
  if (WebPGetFeatures(data.bytes, data.size, &config.input) != VP8_STATUS_OK) {
    LOG(WARNING) << "Failed to get WebP features.";
    return false;
  }
  // Animations are not supported.
  DCHECK_EQ(config.input.has_animation, 0);

  // Allocate correct size for the bitmap based on the WebPBitstreamFeatures.
  bitmap->allocN32Pixels(config.input.width, config.input.height);
  DCHECK_EQ(kPremul_SkAlphaType, bitmap->alphaType());

  // Setup the decoder buffer based on the WebPBitstreamFeatures.
  WebPDecBuffer decoderBuffer;

  DCHECK(config.input.has_alpha);
#if SK_B32_SHIFT  // Output little-endian RGBA pixels (Android).
  decoderBuffer.colorspace = MODE_rgbA;
#else  // Output little-endian BGRA pixels.
  decoderBuffer.colorspace = MODE_bgrA;
#endif
  decoderBuffer.u.RGBA.stride = config.input.width * 4;
  decoderBuffer.u.RGBA.size = decoderBuffer.u.RGBA.stride * config.input.height;

  // Instead of using the default WebPDecBuffer output, make WebPDecode directly
  // write into the SkBitmap.
  decoderBuffer.is_external_memory = 1;
  decoderBuffer.u.RGBA.rgba =
      reinterpret_cast<uint8_t*>(bitmap->getAddr32(0, 0));

  // Set the config up to use the decoding buffer we created.
  config.output = decoderBuffer;

  // Decode the input data into the bitmap buffer.
  bool success = WebPDecode(data.bytes, data.size, &config) == VP8_STATUS_OK;

  // Now free the buffer. It is safe to call this even when the buffer is
  // external and not allocated by WebPDecode.
  WebPFreeDecBuffer(&config.output);

  if (!success) {
    LOG(WARNING) << "Failed to decode WebP data.";
    return false;
  }
  return true;
}

}  // namespace blimp