Tweak libpng encoding parameters to increase speed on very large images.

ui/gfx/codec/png_codec.cc

 // Copyright (c) 2012 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 "ui/gfx/codec/png_codec.h"
 
 #include <stdint.h>
 
 #include "base/logging.h"
 #include "base/macros.h"
@@ skipping 570 matching lines @@
 
   // Make sure to not declare any locals here -- locals in the presence
   // of setjmp() in C++ code makes gcc complain.
 
   if (setjmp(png_jmpbuf(png_ptr))) {
     delete[] row_buffer;
     return false;
   }
 
   png_set_compression_level(png_ptr, compression_level);
+  if (compression_level <= Z_BEST_SPEED)

[dcheng, 2016/04/22 01:14:01]

Alternatively, I could add another parameter to DoLibPngWrite and
EncodeWithCompressionLevel. However, I felt like libpng's filter parameters are
kind of opaque and hard to understand, so I just hardcoded here: the idea is if
you are passing Z_BEST_SPEED, you probably want it to be as fast as possible.

+    png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, PNG_NO_FILTERS);
 
   // Set our callback for libpng to give us the data.
   png_set_write_fn(png_ptr, state, EncoderWriteCallback, FakeFlushCallback);
   png_set_error_fn(png_ptr, NULL, LogLibPNGEncodeError, LogLibPNGEncodeWarning);
 
   png_set_IHDR(png_ptr, info_ptr, width, height, 8, png_output_color_type,
                PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
                PNG_FILTER_TYPE_DEFAULT);
 
 #ifdef PNG_TEXT_SUPPORTED
@@ skipping 195 matching lines @@
 // static
 bool PNGCodec::FastEncodeBGRASkBitmap(const SkBitmap& input,
                                       bool discard_transparency,
                                       std::vector<unsigned char>* output) {
   return InternalEncodeSkBitmap(input,
                                 discard_transparency,
                                 Z_BEST_SPEED,
                                 output);
 }
 
+bool PNGCodec::NoCompressEncodeBGRASkBitmap(
+    const SkBitmap& input,
+    bool discard_transparency,
+    std::vector<unsigned char>* output) {
+  return InternalEncodeSkBitmap(input, discard_transparency, Z_NO_COMPRESSION,
+                                output);
+}
+
 PNGCodec::Comment::Comment(const std::string& k, const std::string& t)
     : key(k), text(t) {
 }
 
 PNGCodec::Comment::~Comment() {
 }
 
 }  // namespace gfx