root/ui/gfx/icon_util.cc

DEFINITIONS

1. BuildResizedImageFamily
2. ConvertImageFamilyToBitmaps
3. CreateHICONFromSkBitmap
4. CreateSkBitmapFromHICON
5. CreateSkBitmapFromIconResource
6. CreateSkBitmapFromHICON
7. CreateCursorFromDIB
8. CreateSkBitmapFromHICONHelper
9. CreateIconFileFromImageFamily
10. PixelsHaveAlpha
11. InitializeBitmapHeader
12. SetSingleIconImageInformation
13. CopySkBitmapBitsIntoIconBuffer
14. ComputeIconFileBufferSize
15. ComputeBitmapSizeComponents

// 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/icon_util.h"

#include "base/file_util.h"
#include "base/files/important_file_writer.h"
#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/win/resource_util.h"
#include "base/win/scoped_gdi_object.h"
#include "base/win/scoped_handle.h"
#include "base/win/scoped_hdc.h"
#include "skia/ext/image_operations.h"
#include "third_party/skia/include/core/SkBitmap.h"
#include "ui/gfx/gdi_util.h"
#include "ui/gfx/image/image.h"
#include "ui/gfx/image/image_family.h"
#include "ui/gfx/size.h"

namespace {

struct ScopedICONINFO : ICONINFO {
  ScopedICONINFO() {
    hbmColor = NULL;
    hbmMask = NULL;
  }

  ~ScopedICONINFO() {
    if (hbmColor)
      ::DeleteObject(hbmColor);
    if (hbmMask)
      ::DeleteObject(hbmMask);
  }
};

// Creates a new ImageFamily, |resized_image_family|, based on the images in
// |image_family|, but containing images of specific dimensions desirable for
// Windows icons. For each desired image dimension, it chooses the most
// appropriate image for that size, and resizes it to the desired size.
// Returns true on success, false on failure. Failure can occur if
// |image_family| is empty, all images in the family have size 0x0, or an image
// has no allocated pixel data.
// |resized_image_family| must be empty.
bool BuildResizedImageFamily(const gfx::ImageFamily& image_family,
                             gfx::ImageFamily* resized_image_family) {
  DCHECK(resized_image_family);
  DCHECK(resized_image_family->empty());

  for (size_t i = 0; i < IconUtil::kNumIconDimensions; ++i) {
    int dimension = IconUtil::kIconDimensions[i];
    gfx::Size size(dimension, dimension);
    const gfx::Image* best = image_family.GetBest(size);
    if (!best || best->IsEmpty()) {
      // Either |image_family| is empty, or all images have size 0x0.
      return false;
    }

    // Optimize for the "Large icons" view in Windows Vista+. This view displays
    // icons at full size if only if there is a 256x256 (kLargeIconSize) image
    // in the .ico file. Otherwise, it shrinks icons to 48x48 (kMediumIconSize).
    if (dimension > IconUtil::kMediumIconSize &&
        best->Width() <= IconUtil::kMediumIconSize &&
        best->Height() <= IconUtil::kMediumIconSize) {
      // There is no source icon larger than 48x48, so do not create any
      // images larger than 48x48. kIconDimensions is sorted in ascending
      // order, so it is safe to break here.
      break;
    }

    if (best->Size() == size) {
      resized_image_family->Add(*best);
    } else {
      // There is no |dimension|x|dimension| source image.
      // Resize this one to the desired size, and insert it.
      SkBitmap best_bitmap = best->AsBitmap();
      // Only kARGB_8888 images are supported.
      // This will also filter out images with no pixels.
      if (best_bitmap.colorType() != kPMColor_SkColorType)
        return false;
      SkBitmap resized_bitmap = skia::ImageOperations::Resize(
          best_bitmap, skia::ImageOperations::RESIZE_LANCZOS3,
          dimension, dimension);
      resized_image_family->Add(gfx::Image::CreateFrom1xBitmap(resized_bitmap));
    }
  }
  return true;
}

// Creates a set of bitmaps from an image family.
// All images smaller than 256x256 are converted to SkBitmaps, and inserted into
// |bitmaps| in order of aspect ratio (thinnest to widest), and then ascending
// size order. If an image of exactly 256x256 is specified, it is converted into
// PNG format and stored in |png_bytes|. Images with width or height larger than
// 256 are ignored.
// |bitmaps| must be an empty vector, and not NULL.
// Returns true on success, false on failure. This fails if any image in
// |image_family| is not a 32-bit ARGB image, or is otherwise invalid.
bool ConvertImageFamilyToBitmaps(
    const gfx::ImageFamily& image_family,
    std::vector<SkBitmap>* bitmaps,
    scoped_refptr<base::RefCountedMemory>* png_bytes) {
  DCHECK(bitmaps != NULL);
  DCHECK(bitmaps->empty());

  for (gfx::ImageFamily::const_iterator it = image_family.begin();
       it != image_family.end(); ++it) {
    const gfx::Image& image = *it;

    // All images should have one of the kIconDimensions sizes.
    DCHECK_GT(image.Width(), 0);
    DCHECK_LE(image.Width(), IconUtil::kLargeIconSize);
    DCHECK_GT(image.Height(), 0);
    DCHECK_LE(image.Height(), IconUtil::kLargeIconSize);

    SkBitmap bitmap = image.AsBitmap();

    // Only 32 bit ARGB bitmaps are supported. We also make sure the bitmap has
    // been properly initialized.
    SkAutoLockPixels bitmap_lock(bitmap);
    if ((bitmap.colorType() != kPMColor_SkColorType) ||
        (bitmap.getPixels() == NULL)) {
      return false;
    }

    // Special case: Icons exactly 256x256 are stored in PNG format.
    if (image.Width() == IconUtil::kLargeIconSize &&
        image.Height() == IconUtil::kLargeIconSize) {
      *png_bytes = image.As1xPNGBytes();
    } else {
      bitmaps->push_back(bitmap);
    }
  }

  return true;
}

}  // namespace

// The icon images appear in the icon file in same order in which their
// corresponding dimensions appear in this array, so it is important to keep
// this array sorted. Also note that the maximum icon image size we can handle
// is 256 by 256. See:
// http://msdn.microsoft.com/en-us/library/windows/desktop/aa511280.aspx#size
const int IconUtil::kIconDimensions[] = {
  8,    // Recommended by the MSDN as a nice to have icon size.
  10,   // Used by the Shell (e.g. for shortcuts).
  14,   // Recommended by the MSDN as a nice to have icon size.
  16,   // Toolbar, Application and Shell icon sizes.
  22,   // Recommended by the MSDN as a nice to have icon size.
  24,   // Used by the Shell (e.g. for shortcuts).
  32,   // Toolbar, Dialog and Wizard icon size.
  40,   // Quick Launch.
  48,   // Alt+Tab icon size.
  64,   // Recommended by the MSDN as a nice to have icon size.
  96,   // Recommended by the MSDN as a nice to have icon size.
  128,  // Used by the Shell (e.g. for shortcuts).
  256   // Used by Vista onwards for large icons.
};

const size_t IconUtil::kNumIconDimensions = arraysize(kIconDimensions);
const size_t IconUtil::kNumIconDimensionsUpToMediumSize = 9;

HICON IconUtil::CreateHICONFromSkBitmap(const SkBitmap& bitmap) {
  // Only 32 bit ARGB bitmaps are supported. We also try to perform as many
  // validations as we can on the bitmap.
  SkAutoLockPixels bitmap_lock(bitmap);
  if ((bitmap.colorType() != kPMColor_SkColorType) ||
      (bitmap.width() <= 0) || (bitmap.height() <= 0) ||
      (bitmap.getPixels() == NULL))
    return NULL;

  // We start by creating a DIB which we'll use later on in order to create
  // the HICON. We use BITMAPV5HEADER since the bitmap we are about to convert
  // may contain an alpha channel and the V5 header allows us to specify the
  // alpha mask for the DIB.
  BITMAPV5HEADER bitmap_header;
  InitializeBitmapHeader(&bitmap_header, bitmap.width(), bitmap.height());
  void* bits;
  HDC hdc = ::GetDC(NULL);
  HBITMAP dib;
  dib = ::CreateDIBSection(hdc, reinterpret_cast<BITMAPINFO*>(&bitmap_header),
                           DIB_RGB_COLORS, &bits, NULL, 0);
  DCHECK(dib);
  ::ReleaseDC(NULL, hdc);
  memcpy(bits, bitmap.getPixels(), bitmap.width() * bitmap.height() * 4);

  // Icons are generally created using an AND and XOR masks where the AND
  // specifies boolean transparency (the pixel is either opaque or
  // transparent) and the XOR mask contains the actual image pixels. If the XOR
  // mask bitmap has an alpha channel, the AND monochrome bitmap won't
  // actually be used for computing the pixel transparency. Even though all our
  // bitmap has an alpha channel, Windows might not agree when all alpha values
  // are zero. So the monochrome bitmap is created with all pixels transparent
  // for this case. Otherwise, it is created with all pixels opaque.
  bool bitmap_has_alpha_channel = PixelsHaveAlpha(
      static_cast<const uint32*>(bitmap.getPixels()),
      bitmap.width() * bitmap.height());

  scoped_ptr<uint8[]> mask_bits;
  if (!bitmap_has_alpha_channel) {
    // Bytes per line with paddings to make it word alignment.
    size_t bytes_per_line = (bitmap.width() + 0xF) / 16 * 2;
    size_t mask_bits_size = bytes_per_line * bitmap.height();

    mask_bits.reset(new uint8[mask_bits_size]);
    DCHECK(mask_bits.get());

    // Make all pixels transparent.
    memset(mask_bits.get(), 0xFF, mask_bits_size);
  }

  HBITMAP mono_bitmap = ::CreateBitmap(bitmap.width(), bitmap.height(), 1, 1,
      reinterpret_cast<LPVOID>(mask_bits.get()));
  DCHECK(mono_bitmap);

  ICONINFO icon_info;
  icon_info.fIcon = TRUE;
  icon_info.xHotspot = 0;
  icon_info.yHotspot = 0;
  icon_info.hbmMask = mono_bitmap;
  icon_info.hbmColor = dib;
  HICON icon = ::CreateIconIndirect(&icon_info);
  ::DeleteObject(dib);
  ::DeleteObject(mono_bitmap);
  return icon;
}

SkBitmap* IconUtil::CreateSkBitmapFromHICON(HICON icon, const gfx::Size& s) {
  // We start with validating parameters.
  if (!icon || s.IsEmpty())
    return NULL;
  ScopedICONINFO icon_info;
  if (!::GetIconInfo(icon, &icon_info))
    return NULL;
  if (!icon_info.fIcon)
    return NULL;
  return new SkBitmap(CreateSkBitmapFromHICONHelper(icon, s));
}

scoped_ptr<SkBitmap> IconUtil::CreateSkBitmapFromIconResource(HMODULE module,
                                                              int resource_id,
                                                              int size) {
  DCHECK_LE(size, kLargeIconSize);

  // For everything except the Vista+ 256x256 icons, use |LoadImage()|.
  if (size != kLargeIconSize) {
    HICON icon_handle =
        static_cast<HICON>(LoadImage(module, MAKEINTRESOURCE(resource_id),
                                     IMAGE_ICON, size, size,
                                     LR_DEFAULTCOLOR | LR_DEFAULTSIZE));
    scoped_ptr<SkBitmap> bitmap(IconUtil::CreateSkBitmapFromHICON(icon_handle));
    DestroyIcon(icon_handle);
    return bitmap.Pass();
  }

  // For Vista+ 256x256 PNG icons, read the resource directly and find
  // the corresponding icon entry to get its PNG bytes.
  void* icon_dir_data = NULL;
  size_t icon_dir_size = 0;
  if (!base::win::GetResourceFromModule(module, resource_id, RT_GROUP_ICON,
                                        &icon_dir_data, &icon_dir_size)) {
    return scoped_ptr<SkBitmap>();
  }
  DCHECK(icon_dir_data);
  DCHECK_GE(icon_dir_size, sizeof(GRPICONDIR));

  const GRPICONDIR* icon_dir =
      reinterpret_cast<const GRPICONDIR*>(icon_dir_data);
  const GRPICONDIRENTRY* large_icon_entry = NULL;
  for (size_t i = 0; i < icon_dir->idCount; ++i) {
    const GRPICONDIRENTRY* entry = &icon_dir->idEntries[i];
    // 256x256 icons are stored with width and height set to 0.
    // See: http://en.wikipedia.org/wiki/ICO_(file_format)
    if (entry->bWidth == 0 && entry->bHeight == 0) {
      large_icon_entry = entry;
      break;
    }
  }
  if (!large_icon_entry)
    return scoped_ptr<SkBitmap>();

  void* png_data = NULL;
  size_t png_size = 0;
  if (!base::win::GetResourceFromModule(module, large_icon_entry->nID, RT_ICON,
                                        &png_data, &png_size)) {
    return scoped_ptr<SkBitmap>();
  }
  DCHECK(png_data);
  DCHECK_EQ(png_size, large_icon_entry->dwBytesInRes);

  gfx::Image image = gfx::Image::CreateFrom1xPNGBytes(
      new base::RefCountedStaticMemory(png_data, png_size));
  return scoped_ptr<SkBitmap>(new SkBitmap(image.AsBitmap()));
}

SkBitmap* IconUtil::CreateSkBitmapFromHICON(HICON icon) {
  // We start with validating parameters.
  if (!icon)
    return NULL;

  ScopedICONINFO icon_info;
  BITMAP bitmap_info = { 0 };

  if (!::GetIconInfo(icon, &icon_info))
    return NULL;

  if (!::GetObject(icon_info.hbmMask, sizeof(bitmap_info), &bitmap_info))
    return NULL;

  gfx::Size icon_size(bitmap_info.bmWidth, bitmap_info.bmHeight);
  return new SkBitmap(CreateSkBitmapFromHICONHelper(icon, icon_size));
}

HICON IconUtil::CreateCursorFromDIB(const gfx::Size& icon_size,
                                    const gfx::Point& hotspot,
                                    const void* dib_bits,
                                    size_t dib_size) {
  BITMAPINFO icon_bitmap_info = {0};
  gfx::CreateBitmapHeader(
      icon_size.width(),
      icon_size.height(),
      reinterpret_cast<BITMAPINFOHEADER*>(&icon_bitmap_info));

  base::win::ScopedGetDC dc(NULL);
  base::win::ScopedCreateDC working_dc(CreateCompatibleDC(dc));
  base::win::ScopedGDIObject<HBITMAP> bitmap_handle(
      CreateDIBSection(dc,
                       &icon_bitmap_info,
                       DIB_RGB_COLORS,
                       0,
                       0,
                       0));
  if (dib_size > 0) {
    SetDIBits(0,
              bitmap_handle,
              0,
              icon_size.height(),
              dib_bits,
              &icon_bitmap_info,
              DIB_RGB_COLORS);
  }

  HBITMAP old_bitmap = reinterpret_cast<HBITMAP>(
      SelectObject(working_dc, bitmap_handle));
  SetBkMode(working_dc, TRANSPARENT);
  SelectObject(working_dc, old_bitmap);

  base::win::ScopedGDIObject<HBITMAP> mask(
      CreateBitmap(icon_size.width(),
                   icon_size.height(),
                   1,
                   1,
                   NULL));
  ICONINFO ii = {0};
  ii.fIcon = FALSE;
  ii.xHotspot = hotspot.x();
  ii.yHotspot = hotspot.y();
  ii.hbmMask = mask;
  ii.hbmColor = bitmap_handle;

  return CreateIconIndirect(&ii);
}

SkBitmap IconUtil::CreateSkBitmapFromHICONHelper(HICON icon,
                                                 const gfx::Size& s) {
  DCHECK(icon);
  DCHECK(!s.IsEmpty());

  // Allocating memory for the SkBitmap object. We are going to create an ARGB
  // bitmap so we should set the configuration appropriately.
  SkBitmap bitmap;
  bitmap.allocN32Pixels(s.width(), s.height());
  bitmap.eraseARGB(0, 0, 0, 0);
  SkAutoLockPixels bitmap_lock(bitmap);

  // Now we should create a DIB so that we can use ::DrawIconEx in order to
  // obtain the icon's image.
  BITMAPV5HEADER h;
  InitializeBitmapHeader(&h, s.width(), s.height());
  HDC hdc = ::GetDC(NULL);
  uint32* bits;
  HBITMAP dib = ::CreateDIBSection(hdc, reinterpret_cast<BITMAPINFO*>(&h),
      DIB_RGB_COLORS, reinterpret_cast<void**>(&bits), NULL, 0);
  DCHECK(dib);
  HDC dib_dc = CreateCompatibleDC(hdc);
  ::ReleaseDC(NULL, hdc);
  DCHECK(dib_dc);
  HGDIOBJ old_obj = ::SelectObject(dib_dc, dib);

  // Windows icons are defined using two different masks. The XOR mask, which
  // represents the icon image and an AND mask which is a monochrome bitmap
  // which indicates the transparency of each pixel.
  //
  // To make things more complex, the icon image itself can be an ARGB bitmap
  // and therefore contain an alpha channel which specifies the transparency
  // for each pixel. Unfortunately, there is no easy way to determine whether
  // or not a bitmap has an alpha channel and therefore constructing the bitmap
  // for the icon is nothing but straightforward.
  //
  // The idea is to read the AND mask but use it only if we know for sure that
  // the icon image does not have an alpha channel. The only way to tell if the
  // bitmap has an alpha channel is by looking through the pixels and checking
  // whether there are non-zero alpha bytes.
  //
  // We start by drawing the AND mask into our DIB.
  size_t num_pixels = s.GetArea();
  memset(bits, 0, num_pixels * 4);
  ::DrawIconEx(dib_dc, 0, 0, icon, s.width(), s.height(), 0, NULL, DI_MASK);

  // Capture boolean opacity. We may not use it if we find out the bitmap has
  // an alpha channel.
  scoped_ptr<bool[]> opaque(new bool[num_pixels]);
  for (size_t i = 0; i < num_pixels; ++i)
    opaque[i] = !bits[i];

  // Then draw the image itself which is really the XOR mask.
  memset(bits, 0, num_pixels * 4);
  ::DrawIconEx(dib_dc, 0, 0, icon, s.width(), s.height(), 0, NULL, DI_NORMAL);
  memcpy(bitmap.getPixels(), static_cast<void*>(bits), num_pixels * 4);

  // Finding out whether the bitmap has an alpha channel.
  bool bitmap_has_alpha_channel = PixelsHaveAlpha(
      static_cast<const uint32*>(bitmap.getPixels()), num_pixels);

  // If the bitmap does not have an alpha channel, we need to build it using
  // the previously captured AND mask. Otherwise, we are done.
  if (!bitmap_has_alpha_channel) {
    uint32* p = static_cast<uint32*>(bitmap.getPixels());
    for (size_t i = 0; i < num_pixels; ++p, ++i) {
      DCHECK_EQ((*p & 0xff000000), 0u);
      if (opaque[i])
        *p |= 0xff000000;
      else
        *p &= 0x00ffffff;
    }
  }

  ::SelectObject(dib_dc, old_obj);
  ::DeleteObject(dib);
  ::DeleteDC(dib_dc);

  return bitmap;
}

// static
bool IconUtil::CreateIconFileFromImageFamily(
    const gfx::ImageFamily& image_family,
    const base::FilePath& icon_path) {
  // Creating a set of bitmaps corresponding to the icon images we'll end up
  // storing in the icon file. Each bitmap is created by resizing the most
  // appropriate image from |image_family| to the desired size.
  gfx::ImageFamily resized_image_family;
  if (!BuildResizedImageFamily(image_family, &resized_image_family))
    return false;

  std::vector<SkBitmap> bitmaps;
  scoped_refptr<base::RefCountedMemory> png_bytes;
  if (!ConvertImageFamilyToBitmaps(resized_image_family, &bitmaps, &png_bytes))
    return false;

  // Guaranteed true because BuildResizedImageFamily will provide at least one
  // image < 256x256.
  DCHECK(!bitmaps.empty());
  size_t bitmap_count = bitmaps.size();  // Not including PNG image.
  // Including PNG image, if any.
  size_t image_count = bitmap_count + (png_bytes.get() ? 1 : 0);

  // Computing the total size of the buffer we need in order to store the
  // images in the desired icon format.
  size_t buffer_size = ComputeIconFileBufferSize(bitmaps);
  // Account for the bytes needed for the PNG entry.
  if (png_bytes.get())
    buffer_size += sizeof(ICONDIRENTRY) + png_bytes->size();

  // Setting the information in the structures residing within the buffer.
  // First, we set the information which doesn't require iterating through the
  // bitmap set and then we set the bitmap specific structures. In the latter
  // step we also copy the actual bits.
  std::vector<uint8> buffer(buffer_size);
  ICONDIR* icon_dir = reinterpret_cast<ICONDIR*>(&buffer[0]);
  icon_dir->idType = kResourceTypeIcon;
  icon_dir->idCount = static_cast<WORD>(image_count);
  // - 1 because there is already one ICONDIRENTRY in ICONDIR.
  size_t icon_dir_count = image_count - 1;

  size_t offset = sizeof(ICONDIR) + (sizeof(ICONDIRENTRY) * icon_dir_count);
  for (size_t i = 0; i < bitmap_count; i++) {
    ICONIMAGE* image = reinterpret_cast<ICONIMAGE*>(&buffer[offset]);
    DCHECK_LT(offset, buffer_size);
    size_t icon_image_size = 0;
    SetSingleIconImageInformation(bitmaps[i], i, icon_dir, image, offset,
                                  &icon_image_size);
    DCHECK_GT(icon_image_size, 0U);
    offset += icon_image_size;
  }

  // Add the PNG entry, if necessary.
  if (png_bytes.get()) {
    ICONDIRENTRY* entry = &icon_dir->idEntries[bitmap_count];
    entry->bWidth = 0;
    entry->bHeight = 0;
    entry->wPlanes = 1;
    entry->wBitCount = 32;
    entry->dwBytesInRes = static_cast<DWORD>(png_bytes->size());
    entry->dwImageOffset = static_cast<DWORD>(offset);
    memcpy(&buffer[offset], png_bytes->front(), png_bytes->size());
    offset += png_bytes->size();
  }

  DCHECK_EQ(offset, buffer_size);

  std::string data(buffer.begin(), buffer.end());
  return base::ImportantFileWriter::WriteFileAtomically(icon_path, data);
}

bool IconUtil::PixelsHaveAlpha(const uint32* pixels, size_t num_pixels) {
  for (const uint32* end = pixels + num_pixels; pixels != end; ++pixels) {
    if ((*pixels & 0xff000000) != 0)
      return true;
  }

  return false;
}

void IconUtil::InitializeBitmapHeader(BITMAPV5HEADER* header, int width,
                                      int height) {
  DCHECK(header);
  memset(header, 0, sizeof(BITMAPV5HEADER));
  header->bV5Size = sizeof(BITMAPV5HEADER);

  // Note that icons are created using top-down DIBs so we must negate the
  // value used for the icon's height.
  header->bV5Width = width;
  header->bV5Height = -height;
  header->bV5Planes = 1;
  header->bV5Compression = BI_RGB;

  // Initializing the bitmap format to 32 bit ARGB.
  header->bV5BitCount = 32;
  header->bV5RedMask = 0x00FF0000;
  header->bV5GreenMask = 0x0000FF00;
  header->bV5BlueMask = 0x000000FF;
  header->bV5AlphaMask = 0xFF000000;

  // Use the system color space.  The default value is LCS_CALIBRATED_RGB, which
  // causes us to crash if we don't specify the approprite gammas, etc.  See
  // <http://msdn.microsoft.com/en-us/library/ms536531(VS.85).aspx> and
  // <http://b/1283121>.
  header->bV5CSType = LCS_WINDOWS_COLOR_SPACE;

  // Use a valid value for bV5Intent as 0 is not a valid one.
  // <http://msdn.microsoft.com/en-us/library/dd183381(VS.85).aspx>
  header->bV5Intent = LCS_GM_IMAGES;
}

void IconUtil::SetSingleIconImageInformation(const SkBitmap& bitmap,
                                             size_t index,
                                             ICONDIR* icon_dir,
                                             ICONIMAGE* icon_image,
                                             size_t image_offset,
                                             size_t* image_byte_count) {
  DCHECK(icon_dir != NULL);
  DCHECK(icon_image != NULL);
  DCHECK_GT(image_offset, 0U);
  DCHECK(image_byte_count != NULL);
  DCHECK_LT(bitmap.width(), kLargeIconSize);
  DCHECK_LT(bitmap.height(), kLargeIconSize);

  // We start by computing certain image values we'll use later on.
  size_t xor_mask_size, bytes_in_resource;
  ComputeBitmapSizeComponents(bitmap,
                              &xor_mask_size,
                              &bytes_in_resource);

  icon_dir->idEntries[index].bWidth = static_cast<BYTE>(bitmap.width());
  icon_dir->idEntries[index].bHeight = static_cast<BYTE>(bitmap.height());
  icon_dir->idEntries[index].wPlanes = 1;
  icon_dir->idEntries[index].wBitCount = 32;
  icon_dir->idEntries[index].dwBytesInRes = bytes_in_resource;
  icon_dir->idEntries[index].dwImageOffset = image_offset;
  icon_image->icHeader.biSize = sizeof(BITMAPINFOHEADER);

  // The width field in the BITMAPINFOHEADER structure accounts for the height
  // of both the AND mask and the XOR mask so we need to multiply the bitmap's
  // height by 2. The same does NOT apply to the width field.
  icon_image->icHeader.biHeight = bitmap.height() * 2;
  icon_image->icHeader.biWidth = bitmap.width();
  icon_image->icHeader.biPlanes = 1;
  icon_image->icHeader.biBitCount = 32;

  // We use a helper function for copying to actual bits from the SkBitmap
  // object into the appropriate space in the buffer. We use a helper function
  // (rather than just copying the bits) because there is no way to specify the
  // orientation (bottom-up vs. top-down) of a bitmap residing in a .ico file.
  // Thus, if we just copy the bits, we'll end up with a bottom up bitmap in
  // the .ico file which will result in the icon being displayed upside down.
  // The helper function copies the image into the buffer one scanline at a
  // time.
  //
  // Note that we don't need to initialize the AND mask since the memory
  // allocated for the icon data buffer was initialized to zero. The icon we
  // create will therefore use an AND mask containing only zeros, which is OK
  // because the underlying image has an alpha channel. An AND mask containing
  // only zeros essentially means we'll initially treat all the pixels as
  // opaque.
  unsigned char* image_addr = reinterpret_cast<unsigned char*>(icon_image);
  unsigned char* xor_mask_addr = image_addr + sizeof(BITMAPINFOHEADER);
  CopySkBitmapBitsIntoIconBuffer(bitmap, xor_mask_addr, xor_mask_size);
  *image_byte_count = bytes_in_resource;
}

void IconUtil::CopySkBitmapBitsIntoIconBuffer(const SkBitmap& bitmap,
                                              unsigned char* buffer,
                                              size_t buffer_size) {
  SkAutoLockPixels bitmap_lock(bitmap);
  unsigned char* bitmap_ptr = static_cast<unsigned char*>(bitmap.getPixels());
  size_t bitmap_size = bitmap.height() * bitmap.width() * 4;
  DCHECK_EQ(buffer_size, bitmap_size);
  for (size_t i = 0; i < bitmap_size; i += bitmap.width() * 4) {
    memcpy(buffer + bitmap_size - bitmap.width() * 4 - i,
           bitmap_ptr + i,
           bitmap.width() * 4);
  }
}

size_t IconUtil::ComputeIconFileBufferSize(const std::vector<SkBitmap>& set) {
  DCHECK(!set.empty());

  // We start by counting the bytes for the structures that don't depend on the
  // number of icon images. Note that sizeof(ICONDIR) already accounts for a
  // single ICONDIRENTRY structure, which is why we subtract one from the
  // number of bitmaps.
  size_t total_buffer_size = sizeof(ICONDIR);
  size_t bitmap_count = set.size();
  total_buffer_size += sizeof(ICONDIRENTRY) * (bitmap_count - 1);
  // May not have all icon sizes, but must have at least up to medium icon size.
  DCHECK_GE(bitmap_count, kNumIconDimensionsUpToMediumSize);

  // Add the bitmap specific structure sizes.
  for (size_t i = 0; i < bitmap_count; i++) {
    size_t xor_mask_size, bytes_in_resource;
    ComputeBitmapSizeComponents(set[i],
                                &xor_mask_size,
                                &bytes_in_resource);
    total_buffer_size += bytes_in_resource;
  }
  return total_buffer_size;
}

void IconUtil::ComputeBitmapSizeComponents(const SkBitmap& bitmap,
                                           size_t* xor_mask_size,
                                           size_t* bytes_in_resource) {
  // The XOR mask size is easy to calculate since we only deal with 32bpp
  // images.
  *xor_mask_size = bitmap.width() * bitmap.height() * 4;

  // Computing the AND mask is a little trickier since it is a monochrome
  // bitmap (regardless of the number of bits per pixels used in the XOR mask).
  // There are two things we must make sure we do when computing the AND mask
  // size:
  //
  // 1. Make sure the right number of bytes is allocated for each AND mask
  //    scan line in case the number of pixels in the image is not divisible by
  //    8. For example, in a 15X15 image, 15 / 8 is one byte short of
  //    containing the number of bits we need in order to describe a single
  //    image scan line so we need to add a byte. Thus, we need 2 bytes instead
  //    of 1 for each scan line.
  //
  // 2. Make sure each scan line in the AND mask is 4 byte aligned (so that the
  //    total icon image has a 4 byte alignment). In the 15X15 image example
  //    above, we can not use 2 bytes so we increase it to the next multiple of
  //    4 which is 4.
  //
  // Once we compute the size for a singe AND mask scan line, we multiply that
  // number by the image height in order to get the total number of bytes for
  // the AND mask. Thus, for a 15X15 image, we need 15 * 4 which is 60 bytes
  // for the monochrome bitmap representing the AND mask.
  size_t and_line_length = (bitmap.width() + 7) >> 3;
  and_line_length = (and_line_length + 3) & ~3;
  size_t and_mask_size = and_line_length * bitmap.height();
  size_t masks_size = *xor_mask_size + and_mask_size;
  *bytes_in_resource = masks_size + sizeof(BITMAPINFOHEADER);
}