Add support for decoding WebP images

ios/web/public/webp_decoder.mm

+// Copyright 2013 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 "ios/web/public/webp_decoder.h"
+
+#import <Foundation/Foundation.h>
+#import <UIKit/UIKit.h>
+
+#include "base/logging.h"
+#include "base/metrics/histogram.h"
+
+namespace {
+
+const uint8_t kNumIfdEntries = 15;
+const unsigned int kExtraDataSize = 16;
+// 10b for signature/header + n * 12b entries + 4b for IFD terminator:
+const unsigned int kExtraDataOffset = 10 + 12 * kNumIfdEntries + 4;
+const unsigned int kHeaderSize = kExtraDataOffset + kExtraDataSize;
+const int kRecompressionThreshold = 64 * 64;  // Threshold in pixels.
+const CGFloat kJpegQuality = 0.85;
+
+// Adapted from libwebp example dwebp.c.
+void PutLE16(uint8_t* const dst, uint32_t value) {
+  dst[0] = (value >> 0) & 0xff;
+  dst[1] = (value >> 8) & 0xff;
+}
+
+void PutLE32(uint8_t* const dst, uint32_t value) {
+  PutLE16(dst + 0, (value >> 0) & 0xffff);
+  PutLE16(dst + 2, (value >> 16) & 0xffff);
+}
+
+void WriteTiffHeader(uint8_t* dst,
+                     int width,
+                     int height,
+                     int bytes_per_px,
+                     bool has_alpha) {
+  // For non-alpha case, we omit tag 0x152 (ExtraSamples).
+  const uint8_t num_ifd_entries = has_alpha ? kNumIfdEntries
+                                            : kNumIfdEntries - 1;
+  uint8_t tiff_header[kHeaderSize] = {
+    0x49, 0x49, 0x2a, 0x00,   // little endian signature
+    8, 0, 0, 0,               // offset to the unique IFD that follows
+    // IFD (offset = 8). Entries must be written in increasing tag order.
+    num_ifd_entries, 0,       // Number of entries in the IFD (12 bytes each).
+    0x00, 0x01, 3, 0, 1, 0, 0, 0, 0, 0, 0, 0,    //  10: Width  (TBD)
+    0x01, 0x01, 3, 0, 1, 0, 0, 0, 0, 0, 0, 0,    //  22: Height (TBD)
+    0x02, 0x01, 3, 0, bytes_per_px, 0, 0, 0,     //  34: BitsPerSample: 8888
+        kExtraDataOffset + 0, 0, 0, 0,
+    0x03, 0x01, 3, 0, 1, 0, 0, 0, 1, 0, 0, 0,    //  46: Compression: none
+    0x06, 0x01, 3, 0, 1, 0, 0, 0, 2, 0, 0, 0,    //  58: Photometric: RGB
+    0x11, 0x01, 4, 0, 1, 0, 0, 0,                //  70: Strips offset:
+        kHeaderSize, 0, 0, 0,                    //      data follows header
+    0x12, 0x01, 3, 0, 1, 0, 0, 0, 1, 0, 0, 0,    //  82: Orientation: topleft
+    0x15, 0x01, 3, 0, 1, 0, 0, 0,                //  94: SamplesPerPixels
+        bytes_per_px, 0, 0, 0,
+    0x16, 0x01, 3, 0, 1, 0, 0, 0, 0, 0, 0, 0,    // 106: Rows per strip (TBD)
+    0x17, 0x01, 4, 0, 1, 0, 0, 0, 0, 0, 0, 0,    // 118: StripByteCount (TBD)
+    0x1a, 0x01, 5, 0, 1, 0, 0, 0,                // 130: X-resolution
+        kExtraDataOffset + 8, 0, 0, 0,
+    0x1b, 0x01, 5, 0, 1, 0, 0, 0,                // 142: Y-resolution
+        kExtraDataOffset + 8, 0, 0, 0,
+    0x1c, 0x01, 3, 0, 1, 0, 0, 0, 1, 0, 0, 0,    // 154: PlanarConfiguration
+    0x28, 0x01, 3, 0, 1, 0, 0, 0, 2, 0, 0, 0,    // 166: ResolutionUnit (inch)
+    0x52, 0x01, 3, 0, 1, 0, 0, 0, 1, 0, 0, 0,    // 178: ExtraSamples: rgbA
+    0, 0, 0, 0,                                  // 190: IFD terminator
+    // kExtraDataOffset:
+    8, 0, 8, 0, 8, 0, 8, 0,      // BitsPerSample
+    72, 0, 0, 0, 1, 0, 0, 0      // 72 pixels/inch, for X/Y-resolution
+  };
+
+  // Fill placeholders in IFD:
+  PutLE32(tiff_header + 10 + 8, width);
+  PutLE32(tiff_header + 22 + 8, height);
+  PutLE32(tiff_header + 106 + 8, height);
+  PutLE32(tiff_header + 118 + 8, width * bytes_per_px * height);
+  if (!has_alpha)
+    PutLE32(tiff_header + 178, 0);
+
+  memcpy(dst, tiff_header, kHeaderSize);
+}
+
+}  // namespace
+
+namespace web {
+
+// static
+size_t WebpDecoder::GetHeaderSize() {
+  return kHeaderSize;
+}
+
+WebpDecoder::WebpDecoder(WebpDecoder::Delegate* delegate)
+    : delegate_(delegate), state_(READING_FEATURES), has_alpha_(0) {
+  DCHECK(delegate_.get());
+  const bool rv = WebPInitDecoderConfig(&config_);
+  DCHECK(rv);
+}
+
+WebpDecoder::~WebpDecoder() {
+  WebPFreeDecBuffer(&config_.output);
+}
+
+void WebpDecoder::OnDataReceived(const base::scoped_nsobject<NSData>& data) {
+  DCHECK(data);
+  switch (state_) {
+    case READING_FEATURES:
+      DoReadFeatures(data);
+      break;
+    case READING_DATA:
+      DoReadData(data);
+      break;
+    case DONE:
+      DLOG(WARNING) << "Received WebP data but decoding is finished. Ignoring.";
+      break;
+  }
+}
+
+void WebpDecoder::Stop() {
+  if (state_ != DONE) {
+    state_ = DONE;
+    DLOG(WARNING) << "Unexpected end of WebP data.";
+    delegate_->OnFinishedDecoding(false);
+  }
+}
+
+void WebpDecoder::DoReadFeatures(NSData* data) {
+  DCHECK_EQ(READING_FEATURES, state_);
+  DCHECK(data);
+  if (features_)
+    [features_ appendData:data];
+  else
+    features_.reset([[NSMutableData alloc] initWithData:data]);
+  VP8StatusCode status =
+      WebPGetFeatures(static_cast<const uint8_t*>([features_ bytes]),
+                      [features_ length], &config_.input);
+  switch (status) {
+    case VP8_STATUS_OK: {
+      has_alpha_ = config_.input.has_alpha;
+      const uint32_t width = config_.input.width;
+      const uint32_t height = config_.input.height;
+      const size_t bytes_per_px = has_alpha_ ? 4 : 3;
+      const int stride = bytes_per_px * width;
+      const size_t image_data_size = stride * height;
+      const size_t total_size = image_data_size + kHeaderSize;
+      // Force pre-multiplied alpha.
+      config_.output.colorspace = has_alpha_ ? MODE_rgbA : MODE_RGB;
+      config_.output.u.RGBA.stride = stride;
+      // Create the output buffer.
+      config_.output.u.RGBA.size = image_data_size;
+      uint8_t* dst = static_cast<uint8_t*>(malloc(total_size));
+      if (!dst) {
+        DLOG(ERROR) << "Could not allocate WebP decoding buffer (size = "
+                    << total_size << ").";
+        delegate_->OnFinishedDecoding(false);
+        state_ = DONE;
+        break;
+      }
+      WriteTiffHeader(dst, width, height, bytes_per_px, has_alpha_);
+      output_buffer_.reset([[NSData alloc] initWithBytesNoCopy:dst
+                                                        length:total_size
+                                                  freeWhenDone:YES]);
+      config_.output.is_external_memory = 1;
+      config_.output.u.RGBA.rgba = dst + kHeaderSize;
+      // Start decoding.
+      state_ = READING_DATA;
+      incremental_decoder_.reset(WebPINewDecoder(&config_.output));
+      DoReadData(features_);
+      features_.reset();
+      break;
+    }
+    case VP8_STATUS_NOT_ENOUGH_DATA:
+      // Do nothing.
+      break;
+    default:
+      DLOG(ERROR) << "Error in WebP image features.";
+      delegate_->OnFinishedDecoding(false);
+      state_ = DONE;
+      break;
+  }
+}
+
+void WebpDecoder::DoReadData(NSData* data) {
+  DCHECK_EQ(READING_DATA, state_);
+  DCHECK(incremental_decoder_);
+  DCHECK(data);
+  VP8StatusCode status = WebPIAppend(incremental_decoder_.get(),
+                                     static_cast<const uint8_t*>([data bytes]),
+                                     [data length]);
+  switch (status) {
+    case VP8_STATUS_SUSPENDED:
+      // Do nothing: re-compression to JPEG or PNG cannot be done incrementally.
+      // Wait for the whole image to be decoded.
+      break;
+    case VP8_STATUS_OK: {
+      bool rv = DoSendData();
+      DLOG_IF(ERROR, !rv) << "Error in WebP image conversion.";
+      state_ = DONE;
+      delegate_->OnFinishedDecoding(rv);
+      break;
+    }
+    default:
+      DLOG(ERROR) << "Error in WebP image decoding.";
+      delegate_->OnFinishedDecoding(false);
+      state_ = DONE;
+      break;
+  }
+}
+
+bool WebpDecoder::DoSendData() {
+  DCHECK_EQ(READING_DATA, state_);
+  int width, height;
+  uint8_t* data_ptr =
+      WebPIDecGetRGB(incremental_decoder_.get(), NULL, &width, &height, NULL);
+  if (!data_ptr)
+    return false;
+  DCHECK_EQ(static_cast<const uint8_t*>([output_buffer_ bytes]) + kHeaderSize,
+            data_ptr);
+  base::scoped_nsobject<NSData> result_data;
+  // When the WebP image is larger than |kRecompressionThreshold| it is
+  // compressed to JPEG or PNG. Otherwise, the uncompressed TIFF is used.
+  DecodedImageFormat format = TIFF;
+  if (width * height > kRecompressionThreshold) {
+    base::scoped_nsobject<UIImage> tiff_image(
+        [[UIImage alloc] initWithData:output_buffer_]);
+    if (!tiff_image)
+      return false;
+    // Compress to PNG if the image is transparent, JPEG otherwise.
+    // TODO(droger): Use PNG instead of JPEG if the WebP image is lossless.
+    if (has_alpha_) {
+      result_data.reset([UIImagePNGRepresentation(tiff_image) retain]);
+      format = PNG;
+    } else {
+      result_data.reset(
+          [UIImageJPEGRepresentation(tiff_image, kJpegQuality) retain]);
+      format = JPEG;
+    }
+    if (!result_data)
+      return false;
+  } else {
+    result_data.reset([output_buffer_ retain]);
+  }
+  UMA_HISTOGRAM_ENUMERATION(
+      "WebP.DecodedImageFormat", format, DECODED_FORMAT_COUNT);
+  delegate_->SetImageFeatures([result_data length], format);
+  delegate_->OnDataDecoded(result_data);
+  output_buffer_.reset();
+  return true;
+}
+
+}  // namespace web