optimize-ico-files: Automatically convert large BMPs to PNG format.

tools/resources/ico_tools.py

 # Copyright 2015 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.
 
 import logging
 import math
 import os
 import struct
 import subprocess
 import sys
 import tempfile
 
 OPTIMIZE_PNG_FILES = 'tools/resources/optimize-png-files.sh'
+IMAGEMAGICK_CONVERT = 'convert'
 
 logging.basicConfig(level=logging.INFO, format='%(levelname)s: %(message)s')
 
 class InvalidFile(Exception):
   """Represents an invalid ICO file."""
 
 def IsPng(png_data):
   """Determines whether a sequence of bytes is a PNG."""
   return png_data.startswith('\x89PNG\r\n\x1a\n')
 
@@ skipping 38 matching lines @@
     with open(png_filename, 'wb') as png_file:
       png_file.write(png_data)
     return OptimizePngFile(temp_dir, png_filename,
                            optimization_level=optimization_level)
 
   finally:
     if os.path.exists(png_filename):
       os.unlink(png_filename)
     os.rmdir(temp_dir)
 
+def ExportSingleEntry(icon_dir_entry, icon_data, outfile):
+  """Export a single icon dir entry to its own ICO file.
+
+  Args:
+    icon_dir_entry: Struct containing the fields of an ICONDIRENTRY.
+    icon_data: Raw pixel data of the icon.
+    outfile: File object to write to.
+  """
+  # Write the ICONDIR header.
+  logging.debug('len(icon_data) = %d', len(icon_data))
+  outfile.write(struct.pack('<HHH', 0, 1, 1))
+
+  # Write the ICONDIRENTRY header.
+  width, height, num_colors, r1, r2, r3, size, _ = icon_dir_entry
+  offset = 22;
+  icon_dir_entry = width, height, num_colors, r1, r2, r3, size, offset
+  outfile.write(struct.pack('<BBBBHHLL', *icon_dir_entry))
+
+  # Write the image data.
+  outfile.write(icon_data)
+
+def ConvertIcoToPng(ico_filename, png_filename):
+  """Convert a single-entry ICO file to a PNG image.
+
+  Requires that the user has `convert` (ImageMagick) installed.
+
+  Raises:
+    OSError: If ImageMagick was not found.
+    subprocess.CalledProcessError: If convert failed.
+  """
+  logging.debug('Converting BMP image to PNG...')
+  args = [IMAGEMAGICK_CONVERT, ico_filename, png_filename]
+  result = subprocess.check_call(args, stdout=sys.stderr)
+  logging.info('Converted BMP image to PNG format')
+
+def OptimizeBmp(icon_dir_entry, icon_data):
+  """Convert a BMP file to PNG and optimize it.
+
+  Args:
+    icon_dir_entry: Struct containing the fields of an ICONDIRENTRY.
+    icon_data: Raw pixel data of the icon.
+
+  Returns:
+    The raw bytes of a PNG file, an optimized version of the input.
+  """
+  temp_dir = tempfile.mkdtemp()
+  try:
+    logging.debug('temp_dir = %s', temp_dir)
+    ico_filename = os.path.join(temp_dir, 'image.ico')
+    png_filename = os.path.join(temp_dir, 'image.png')
+    with open(ico_filename, 'wb') as ico_file:
+      logging.debug('writing %s', ico_filename)
+      ExportSingleEntry(icon_dir_entry, icon_data, ico_file)
+
+    try:
+      ConvertIcoToPng(ico_filename, png_filename)
+    except Exception as e:
+      logging.warning('Could not convert BMP to PNG format: %s', e)
+      if isinstance(e, OSError):
+        logging.info('This is because ImageMagick (`convert`) was not found. '
+                     'Please install it, or manually convert large BMP images '
+                     'into PNG before running this utility.')
+      return icon_data
+
+    return OptimizePngFile(temp_dir, png_filename)
+
+  finally:
+    if os.path.exists(ico_filename):
+      os.unlink(ico_filename)
+    if os.path.exists(png_filename):
+      os.unlink(png_filename)
+    os.rmdir(temp_dir)
+
 def ComputeANDMaskFromAlpha(image_data, width, height):
   """Compute an AND mask from 32-bit BGRA image data."""
   and_bytes = []
   for y in range(height):
     bit_count = 0
     current_byte = 0
     for x in range(width):
       alpha = image_data[(y * width + x) * 4 + 3]
       current_byte <<= 1
       if ord(alpha) == 0:
@@ skipping 86 matching lines @@
     offset = current_offset
     icon_data = infile.read(size)
     if len(icon_data) != size:
       raise EOFError()
 
     entry_is_png = IsPng(icon_data)
     logging.info('%s entry #%d: %dx%d, %d bytes (%s)', filename, i + 1, width,
                  height, size, 'PNG' if entry_is_png else 'BMP')
 
     if entry_is_png:
+      # It is a PNG. Crush it.
       icon_data = OptimizePng(icon_data, optimization_level=optimization_level)
+    elif width >= 256 or height >= 256:
+      # It is a large BMP. Reformat as a PNG, then crush it.
+      # Note: Smaller images must be kept uncompressed, for compatibility
+      # with Windows XP.

[scottmg, 2016/11/07 17:45:35]

If this is really the only reason for this restriction, we could remove it now?

[Matt Giuca, 2016/11/08 00:06:31]

That's a great suggestion. I think so, but I'd have to do some research and
testing to make sure. (It's a bit scary to remove the uncompressed icons since
they are the lowest common denominator of Windows icons. For example,
compressing all the icons makes them unreadable with the Linux browser; not that
that really matters but it's an example of things that can break.) I've filed a
bug for it (https://crbug.com/663136) but I think we should land this change
first.

+      icon_data = OptimizeBmp(icon_dir_entries[i], icon_data)
     else:
       new_icon_data = RebuildANDMask(icon_data)
       if new_icon_data != icon_data:
         logging.info('  * Rebuilt AND mask for this image from alpha channel.')
         icon_data = new_icon_data
 
-      if width >= 256 or height >= 256:
-        # TODO(mgiuca): Automatically convert large BMP images to PNGs.
-        logging.warning('Entry #%d is a large image in uncompressed BMP '
-                        'format. Please manually convert to PNG format before '
-                        'running this utility.', i + 1)
-
     new_size = len(icon_data)
     current_offset += new_size
     icon_dir_entries[i] = (width % 256, height % 256, num_colors, r1, r2, r3,
                            new_size, offset)
     icon_bitmap_data.append(icon_data)
 
   # Write the data back to outfile.
   outfile.write(icondir)
   for icon_dir_entry in icon_dir_entries:
     outfile.write(struct.pack('<BBBBHHLL', *icon_dir_entry))
   for icon_bitmap in icon_bitmap_data:
     outfile.write(icon_bitmap)