root/ui/gfx/skbitmap_operations.cc

DEFINITIONS

1. CreateInvertedBitmap
2. CreateSuperimposedBitmap
3. CreateBlendedBitmap
4. CreateMaskedBitmap
5. CreateButtonBackground
6. LineProcDefault
7. LineProcCopy
8. LineProcHnopSnopLdec
9. LineProcHnopSnopLinc
10. LineProcHnopSdecLnop
11. LineProcHnopSdecLdec
12. LineProcHnopSdecLinc
13. CreateHSLShiftedBitmap
14. CreateTiledBitmap
15. DownsampleByTwoUntilSize
16. DownsampleByTwo
17. UnPreMultiply
18. CreateTransposedBitmap
19. CreateColorMask
20. CreateDropShadow
21. Rotate

// 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/skbitmap_operations.h"

#include <algorithm>
#include <string.h>

#include "base/logging.h"
#include "skia/ext/refptr.h"
#include "third_party/skia/include/core/SkBitmap.h"
#include "third_party/skia/include/core/SkCanvas.h"
#include "third_party/skia/include/core/SkColorFilter.h"
#include "third_party/skia/include/core/SkColorPriv.h"
#include "third_party/skia/include/core/SkUnPreMultiply.h"
#include "third_party/skia/include/effects/SkBlurImageFilter.h"
#include "ui/gfx/insets.h"
#include "ui/gfx/point.h"
#include "ui/gfx/size.h"

// static
SkBitmap SkBitmapOperations::CreateInvertedBitmap(const SkBitmap& image) {
  DCHECK(image.colorType() == kPMColor_SkColorType);

  SkAutoLockPixels lock_image(image);

  SkBitmap inverted;
  inverted.allocN32Pixels(image.width(), image.height());
  inverted.eraseARGB(0, 0, 0, 0);

  for (int y = 0; y < image.height(); ++y) {
    uint32* image_row = image.getAddr32(0, y);
    uint32* dst_row = inverted.getAddr32(0, y);

    for (int x = 0; x < image.width(); ++x) {
      uint32 image_pixel = image_row[x];
      dst_row[x] = (image_pixel & 0xFF000000) |
                   (0x00FFFFFF - (image_pixel & 0x00FFFFFF));
    }
  }

  return inverted;
}

// static
SkBitmap SkBitmapOperations::CreateSuperimposedBitmap(const SkBitmap& first,
                                                      const SkBitmap& second) {
  DCHECK(first.width() == second.width());
  DCHECK(first.height() == second.height());
  DCHECK(first.bytesPerPixel() == second.bytesPerPixel());
  DCHECK(first.colorType() == kPMColor_SkColorType);

  SkAutoLockPixels lock_first(first);
  SkAutoLockPixels lock_second(second);

  SkBitmap superimposed;
  superimposed.allocN32Pixels(first.width(), first.height());
  superimposed.eraseARGB(0, 0, 0, 0);

  SkCanvas canvas(superimposed);

  SkRect rect;
  rect.fLeft = 0;
  rect.fTop = 0;
  rect.fRight = SkIntToScalar(first.width());
  rect.fBottom = SkIntToScalar(first.height());

  canvas.drawBitmapRect(first, NULL, rect);
  canvas.drawBitmapRect(second, NULL, rect);

  return superimposed;
}

// static
SkBitmap SkBitmapOperations::CreateBlendedBitmap(const SkBitmap& first,
                                                 const SkBitmap& second,
                                                 double alpha) {
  DCHECK((alpha >= 0) && (alpha <= 1));
  DCHECK(first.width() == second.width());
  DCHECK(first.height() == second.height());
  DCHECK(first.bytesPerPixel() == second.bytesPerPixel());
  DCHECK(first.colorType() == kPMColor_SkColorType);

  // Optimize for case where we won't need to blend anything.
  static const double alpha_min = 1.0 / 255;
  static const double alpha_max = 254.0 / 255;
  if (alpha < alpha_min)
    return first;
  else if (alpha > alpha_max)
    return second;

  SkAutoLockPixels lock_first(first);
  SkAutoLockPixels lock_second(second);

  SkBitmap blended;
  blended.allocN32Pixels(first.width(), first.height());
  blended.eraseARGB(0, 0, 0, 0);

  double first_alpha = 1 - alpha;

  for (int y = 0; y < first.height(); ++y) {
    uint32* first_row = first.getAddr32(0, y);
    uint32* second_row = second.getAddr32(0, y);
    uint32* dst_row = blended.getAddr32(0, y);

    for (int x = 0; x < first.width(); ++x) {
      uint32 first_pixel = first_row[x];
      uint32 second_pixel = second_row[x];

      int a = static_cast<int>((SkColorGetA(first_pixel) * first_alpha) +
                               (SkColorGetA(second_pixel) * alpha));
      int r = static_cast<int>((SkColorGetR(first_pixel) * first_alpha) +
                               (SkColorGetR(second_pixel) * alpha));
      int g = static_cast<int>((SkColorGetG(first_pixel) * first_alpha) +
                               (SkColorGetG(second_pixel) * alpha));
      int b = static_cast<int>((SkColorGetB(first_pixel) * first_alpha) +
                               (SkColorGetB(second_pixel) * alpha));

      dst_row[x] = SkColorSetARGB(a, r, g, b);
    }
  }

  return blended;
}

// static
SkBitmap SkBitmapOperations::CreateMaskedBitmap(const SkBitmap& rgb,
                                                const SkBitmap& alpha) {
  DCHECK(rgb.width() == alpha.width());
  DCHECK(rgb.height() == alpha.height());
  DCHECK(rgb.bytesPerPixel() == alpha.bytesPerPixel());
  DCHECK(rgb.colorType() == kPMColor_SkColorType);
  DCHECK(alpha.colorType() == kPMColor_SkColorType);

  SkBitmap masked;
  masked.allocN32Pixels(rgb.width(), rgb.height());
  masked.eraseARGB(0, 0, 0, 0);

  SkAutoLockPixels lock_rgb(rgb);
  SkAutoLockPixels lock_alpha(alpha);
  SkAutoLockPixels lock_masked(masked);

  for (int y = 0; y < masked.height(); ++y) {
    uint32* rgb_row = rgb.getAddr32(0, y);
    uint32* alpha_row = alpha.getAddr32(0, y);
    uint32* dst_row = masked.getAddr32(0, y);

    for (int x = 0; x < masked.width(); ++x) {
      SkColor rgb_pixel = SkUnPreMultiply::PMColorToColor(rgb_row[x]);
      SkColor alpha_pixel = SkUnPreMultiply::PMColorToColor(alpha_row[x]);
      int alpha = SkAlphaMul(SkColorGetA(rgb_pixel),
                             SkAlpha255To256(SkColorGetA(alpha_pixel)));
      int alpha_256 = SkAlpha255To256(alpha);
      dst_row[x] = SkColorSetARGB(alpha,
                                  SkAlphaMul(SkColorGetR(rgb_pixel), alpha_256),
                                  SkAlphaMul(SkColorGetG(rgb_pixel), alpha_256),
                                  SkAlphaMul(SkColorGetB(rgb_pixel),
                                             alpha_256));
    }
  }

  return masked;
}

// static
SkBitmap SkBitmapOperations::CreateButtonBackground(SkColor color,
                                                    const SkBitmap& image,
                                                    const SkBitmap& mask) {
  DCHECK(image.colorType() == kPMColor_SkColorType);
  DCHECK(mask.colorType() == kPMColor_SkColorType);

  SkBitmap background;
  background.allocN32Pixels(mask.width(), mask.height());

  double bg_a = SkColorGetA(color);
  double bg_r = SkColorGetR(color);
  double bg_g = SkColorGetG(color);
  double bg_b = SkColorGetB(color);

  SkAutoLockPixels lock_mask(mask);
  SkAutoLockPixels lock_image(image);
  SkAutoLockPixels lock_background(background);

  for (int y = 0; y < mask.height(); ++y) {
    uint32* dst_row = background.getAddr32(0, y);
    uint32* image_row = image.getAddr32(0, y % image.height());
    uint32* mask_row = mask.getAddr32(0, y);

    for (int x = 0; x < mask.width(); ++x) {
      uint32 image_pixel = image_row[x % image.width()];

      double img_a = SkColorGetA(image_pixel);
      double img_r = SkColorGetR(image_pixel);
      double img_g = SkColorGetG(image_pixel);
      double img_b = SkColorGetB(image_pixel);

      double img_alpha = static_cast<double>(img_a) / 255.0;
      double img_inv = 1 - img_alpha;

      double mask_a = static_cast<double>(SkColorGetA(mask_row[x])) / 255.0;

      dst_row[x] = SkColorSetARGB(
          static_cast<int>(std::min(255.0, bg_a + img_a) * mask_a),
          static_cast<int>(((bg_r * img_inv) + (img_r * img_alpha)) * mask_a),
          static_cast<int>(((bg_g * img_inv) + (img_g * img_alpha)) * mask_a),
          static_cast<int>(((bg_b * img_inv) + (img_b * img_alpha)) * mask_a));
    }
  }

  return background;
}

namespace {
namespace HSLShift {

// TODO(viettrungluu): Some things have yet to be optimized at all.

// Notes on and conventions used in the following code
//
// Conventions:
//  - R, G, B, A = obvious; as variables: |r|, |g|, |b|, |a| (see also below)
//  - H, S, L = obvious; as variables: |h|, |s|, |l| (see also below)
//  - variables derived from S, L shift parameters: |sdec| and |sinc| for S
//    increase and decrease factors, |ldec| and |linc| for L (see also below)
//
// To try to optimize HSL shifts, we do several things:
//  - Avoid unpremultiplying (then processing) then premultiplying. This means
//    that R, G, B values (and also L, but not H and S) should be treated as
//    having a range of 0..A (where A is alpha).
//  - Do things in integer/fixed-point. This avoids costly conversions between
//    floating-point and integer, though I should study the tradeoff more
//    carefully (presumably, at some point of processing complexity, converting
//    and processing using simpler floating-point code will begin to win in
//    performance). Also to be studied is the speed/type of floating point
//    conversions; see, e.g., <http://www.stereopsis.com/sree/fpu2006.html>.
//
// Conventions for fixed-point arithmetic
//  - Each function has a constant denominator (called |den|, which should be a
//    power of 2), appropriate for the computations done in that function.
//  - A value |x| is then typically represented by a numerator, named |x_num|,
//    so that its actual value is |x_num / den| (casting to floating-point
//    before division).
//  - To obtain |x_num| from |x|, simply multiply by |den|, i.e., |x_num = x *
//    den| (casting appropriately).
//  - When necessary, a value |x| may also be represented as a numerator over
//    the denominator squared (set |den2 = den * den|). In such a case, the
//    corresponding variable is called |x_num2| (so that its actual value is
//    |x_num^2 / den2|.
//  - The representation of the product of |x| and |y| is be called |x_y_num| if
//    |x * y == x_y_num / den|, and |xy_num2| if |x * y == x_y_num2 / den2|. In
//    the latter case, notice that one can calculate |x_y_num2 = x_num * y_num|.

// Routine used to process a line; typically specialized for specific kinds of
// HSL shifts (to optimize).
typedef void (*LineProcessor)(const color_utils::HSL&,
                              const SkPMColor*,
                              SkPMColor*,
                              int width);

enum OperationOnH { kOpHNone = 0, kOpHShift, kNumHOps };
enum OperationOnS { kOpSNone = 0, kOpSDec, kOpSInc, kNumSOps };
enum OperationOnL { kOpLNone = 0, kOpLDec, kOpLInc, kNumLOps };

// Epsilon used to judge when shift values are close enough to various critical
// values (typically 0.5, which yields a no-op for S and L shifts. 1/256 should
// be small enough, but let's play it safe>
const double epsilon = 0.0005;

// Line processor: default/universal (i.e., old-school).
void LineProcDefault(const color_utils::HSL& hsl_shift,
                     const SkPMColor* in,
                     SkPMColor* out,
                     int width) {
  for (int x = 0; x < width; x++) {
    out[x] = SkPreMultiplyColor(color_utils::HSLShift(
        SkUnPreMultiply::PMColorToColor(in[x]), hsl_shift));
  }
}

// Line processor: no-op (i.e., copy).
void LineProcCopy(const color_utils::HSL& hsl_shift,
                  const SkPMColor* in,
                  SkPMColor* out,
                  int width) {
  DCHECK(hsl_shift.h < 0);
  DCHECK(hsl_shift.s < 0 || fabs(hsl_shift.s - 0.5) < HSLShift::epsilon);
  DCHECK(hsl_shift.l < 0 || fabs(hsl_shift.l - 0.5) < HSLShift::epsilon);
  memcpy(out, in, static_cast<size_t>(width) * sizeof(out[0]));
}

// Line processor: H no-op, S no-op, L decrease.
void LineProcHnopSnopLdec(const color_utils::HSL& hsl_shift,
                          const SkPMColor* in,
                          SkPMColor* out,
                          int width) {
  const uint32_t den = 65536;

  DCHECK(hsl_shift.h < 0);
  DCHECK(hsl_shift.s < 0 || fabs(hsl_shift.s - 0.5) < HSLShift::epsilon);
  DCHECK(hsl_shift.l <= 0.5 - HSLShift::epsilon && hsl_shift.l >= 0);

  uint32_t ldec_num = static_cast<uint32_t>(hsl_shift.l * 2 * den);
  for (int x = 0; x < width; x++) {
    uint32_t a = SkGetPackedA32(in[x]);
    uint32_t r = SkGetPackedR32(in[x]);
    uint32_t g = SkGetPackedG32(in[x]);
    uint32_t b = SkGetPackedB32(in[x]);
    r = r * ldec_num / den;
    g = g * ldec_num / den;
    b = b * ldec_num / den;
    out[x] = SkPackARGB32(a, r, g, b);
  }
}

// Line processor: H no-op, S no-op, L increase.
void LineProcHnopSnopLinc(const color_utils::HSL& hsl_shift,
                          const SkPMColor* in,
                          SkPMColor* out,
                          int width) {
  const uint32_t den = 65536;

  DCHECK(hsl_shift.h < 0);
  DCHECK(hsl_shift.s < 0 || fabs(hsl_shift.s - 0.5) < HSLShift::epsilon);
  DCHECK(hsl_shift.l >= 0.5 + HSLShift::epsilon && hsl_shift.l <= 1);

  uint32_t linc_num = static_cast<uint32_t>((hsl_shift.l - 0.5) * 2 * den);
  for (int x = 0; x < width; x++) {
    uint32_t a = SkGetPackedA32(in[x]);
    uint32_t r = SkGetPackedR32(in[x]);
    uint32_t g = SkGetPackedG32(in[x]);
    uint32_t b = SkGetPackedB32(in[x]);
    r += (a - r) * linc_num / den;
    g += (a - g) * linc_num / den;
    b += (a - b) * linc_num / den;
    out[x] = SkPackARGB32(a, r, g, b);
  }
}

// Saturation changes modifications in RGB
//
// (Note that as a further complication, the values we deal in are
// premultiplied, so R/G/B values must be in the range 0..A. For mathematical
// purposes, one may as well use r=R/A, g=G/A, b=B/A. Without loss of
// generality, assume that R/G/B values are in the range 0..1.)
//
// Let Max = max(R,G,B), Min = min(R,G,B), and Med be the median value. Then L =
// (Max+Min)/2. If L is to remain constant, Max+Min must also remain constant.
//
// For H to remain constant, first, the (numerical) order of R/G/B (from
// smallest to largest) must remain the same. Second, all the ratios
// (R-G)/(Max-Min), (R-B)/(Max-Min), (G-B)/(Max-Min) must remain constant (of
// course, if Max = Min, then S = 0 and no saturation change is well-defined,
// since H is not well-defined).
//
// Let C_max be a colour with value Max, C_min be one with value Min, and C_med
// the remaining colour. Increasing saturation (to the maximum) is accomplished
// by increasing the value of C_max while simultaneously decreasing C_min and
// changing C_med so that the ratios are maintained; for the latter, it suffices
// to keep (C_med-C_min)/(C_max-C_min) constant (and equal to
// (Med-Min)/(Max-Min)).

// Line processor: H no-op, S decrease, L no-op.
void LineProcHnopSdecLnop(const color_utils::HSL& hsl_shift,
                          const SkPMColor* in,
                          SkPMColor* out,
                          int width) {
  DCHECK(hsl_shift.h < 0);
  DCHECK(hsl_shift.s >= 0 && hsl_shift.s <= 0.5 - HSLShift::epsilon);
  DCHECK(hsl_shift.l < 0 || fabs(hsl_shift.l - 0.5) < HSLShift::epsilon);

  const int32_t denom = 65536;
  int32_t s_numer = static_cast<int32_t>(hsl_shift.s * 2 * denom);
  for (int x = 0; x < width; x++) {
    int32_t a = static_cast<int32_t>(SkGetPackedA32(in[x]));
    int32_t r = static_cast<int32_t>(SkGetPackedR32(in[x]));
    int32_t g = static_cast<int32_t>(SkGetPackedG32(in[x]));
    int32_t b = static_cast<int32_t>(SkGetPackedB32(in[x]));

    int32_t vmax, vmin;
    if (r > g) {  // This uses 3 compares rather than 4.
      vmax = std::max(r, b);
      vmin = std::min(g, b);
    } else {
      vmax = std::max(g, b);
      vmin = std::min(r, b);
    }

    // Use denom * L to avoid rounding.
    int32_t denom_l = (vmax + vmin) * (denom / 2);
    int32_t s_numer_l = (vmax + vmin) * s_numer / 2;

    r = (denom_l + r * s_numer - s_numer_l) / denom;
    g = (denom_l + g * s_numer - s_numer_l) / denom;
    b = (denom_l + b * s_numer - s_numer_l) / denom;
    out[x] = SkPackARGB32(a, r, g, b);
  }
}

// Line processor: H no-op, S decrease, L decrease.
void LineProcHnopSdecLdec(const color_utils::HSL& hsl_shift,
                          const SkPMColor* in,
                          SkPMColor* out,
                          int width) {
  DCHECK(hsl_shift.h < 0);
  DCHECK(hsl_shift.s >= 0 && hsl_shift.s <= 0.5 - HSLShift::epsilon);
  DCHECK(hsl_shift.l >= 0 && hsl_shift.l <= 0.5 - HSLShift::epsilon);

  // Can't be too big since we need room for denom*denom and a bit for sign.
  const int32_t denom = 1024;
  int32_t l_numer = static_cast<int32_t>(hsl_shift.l * 2 * denom);
  int32_t s_numer = static_cast<int32_t>(hsl_shift.s * 2 * denom);
  for (int x = 0; x < width; x++) {
    int32_t a = static_cast<int32_t>(SkGetPackedA32(in[x]));
    int32_t r = static_cast<int32_t>(SkGetPackedR32(in[x]));
    int32_t g = static_cast<int32_t>(SkGetPackedG32(in[x]));
    int32_t b = static_cast<int32_t>(SkGetPackedB32(in[x]));

    int32_t vmax, vmin;
    if (r > g) {  // This uses 3 compares rather than 4.
      vmax = std::max(r, b);
      vmin = std::min(g, b);
    } else {
      vmax = std::max(g, b);
      vmin = std::min(r, b);
    }

    // Use denom * L to avoid rounding.
    int32_t denom_l = (vmax + vmin) * (denom / 2);
    int32_t s_numer_l = (vmax + vmin) * s_numer / 2;

    r = (denom_l + r * s_numer - s_numer_l) * l_numer / (denom * denom);
    g = (denom_l + g * s_numer - s_numer_l) * l_numer / (denom * denom);
    b = (denom_l + b * s_numer - s_numer_l) * l_numer / (denom * denom);
    out[x] = SkPackARGB32(a, r, g, b);
  }
}

// Line processor: H no-op, S decrease, L increase.
void LineProcHnopSdecLinc(const color_utils::HSL& hsl_shift,
                          const SkPMColor* in,
                          SkPMColor* out,
                          int width) {
  DCHECK(hsl_shift.h < 0);
  DCHECK(hsl_shift.s >= 0 && hsl_shift.s <= 0.5 - HSLShift::epsilon);
  DCHECK(hsl_shift.l >= 0.5 + HSLShift::epsilon && hsl_shift.l <= 1);

  // Can't be too big since we need room for denom*denom and a bit for sign.
  const int32_t denom = 1024;
  int32_t l_numer = static_cast<int32_t>((hsl_shift.l - 0.5) * 2 * denom);
  int32_t s_numer = static_cast<int32_t>(hsl_shift.s * 2 * denom);
  for (int x = 0; x < width; x++) {
    int32_t a = static_cast<int32_t>(SkGetPackedA32(in[x]));
    int32_t r = static_cast<int32_t>(SkGetPackedR32(in[x]));
    int32_t g = static_cast<int32_t>(SkGetPackedG32(in[x]));
    int32_t b = static_cast<int32_t>(SkGetPackedB32(in[x]));

    int32_t vmax, vmin;
    if (r > g) {  // This uses 3 compares rather than 4.
      vmax = std::max(r, b);
      vmin = std::min(g, b);
    } else {
      vmax = std::max(g, b);
      vmin = std::min(r, b);
    }

    // Use denom * L to avoid rounding.
    int32_t denom_l = (vmax + vmin) * (denom / 2);
    int32_t s_numer_l = (vmax + vmin) * s_numer / 2;

    r = denom_l + r * s_numer - s_numer_l;
    g = denom_l + g * s_numer - s_numer_l;
    b = denom_l + b * s_numer - s_numer_l;

    r = (r * denom + (a * denom - r) * l_numer) / (denom * denom);
    g = (g * denom + (a * denom - g) * l_numer) / (denom * denom);
    b = (b * denom + (a * denom - b) * l_numer) / (denom * denom);
    out[x] = SkPackARGB32(a, r, g, b);
  }
}

const LineProcessor kLineProcessors[kNumHOps][kNumSOps][kNumLOps] = {
  { // H: kOpHNone
    { // S: kOpSNone
      LineProcCopy,         // L: kOpLNone
      LineProcHnopSnopLdec, // L: kOpLDec
      LineProcHnopSnopLinc  // L: kOpLInc
    },
    { // S: kOpSDec
      LineProcHnopSdecLnop, // L: kOpLNone
      LineProcHnopSdecLdec, // L: kOpLDec
      LineProcHnopSdecLinc  // L: kOpLInc
    },
    { // S: kOpSInc
      LineProcDefault, // L: kOpLNone
      LineProcDefault, // L: kOpLDec
      LineProcDefault  // L: kOpLInc
    }
  },
  { // H: kOpHShift
    { // S: kOpSNone
      LineProcDefault, // L: kOpLNone
      LineProcDefault, // L: kOpLDec
      LineProcDefault  // L: kOpLInc
    },
    { // S: kOpSDec
      LineProcDefault, // L: kOpLNone
      LineProcDefault, // L: kOpLDec
      LineProcDefault  // L: kOpLInc
    },
    { // S: kOpSInc
      LineProcDefault, // L: kOpLNone
      LineProcDefault, // L: kOpLDec
      LineProcDefault  // L: kOpLInc
    }
  }
};

}  // namespace HSLShift
}  // namespace

// static
SkBitmap SkBitmapOperations::CreateHSLShiftedBitmap(
    const SkBitmap& bitmap,
    const color_utils::HSL& hsl_shift) {
  // Default to NOPs.
  HSLShift::OperationOnH H_op = HSLShift::kOpHNone;
  HSLShift::OperationOnS S_op = HSLShift::kOpSNone;
  HSLShift::OperationOnL L_op = HSLShift::kOpLNone;

  if (hsl_shift.h >= 0 && hsl_shift.h <= 1)
    H_op = HSLShift::kOpHShift;

  // Saturation shift: 0 -> fully desaturate, 0.5 -> NOP, 1 -> fully saturate.
  if (hsl_shift.s >= 0 && hsl_shift.s <= (0.5 - HSLShift::epsilon))
    S_op = HSLShift::kOpSDec;
  else if (hsl_shift.s >= (0.5 + HSLShift::epsilon))
    S_op = HSLShift::kOpSInc;

  // Lightness shift: 0 -> black, 0.5 -> NOP, 1 -> white.
  if (hsl_shift.l >= 0 && hsl_shift.l <= (0.5 - HSLShift::epsilon))
    L_op = HSLShift::kOpLDec;
  else if (hsl_shift.l >= (0.5 + HSLShift::epsilon))
    L_op = HSLShift::kOpLInc;

  HSLShift::LineProcessor line_proc =
      HSLShift::kLineProcessors[H_op][S_op][L_op];

  DCHECK(bitmap.empty() == false);
  DCHECK(bitmap.colorType() == kPMColor_SkColorType);

  SkBitmap shifted;
  shifted.allocN32Pixels(bitmap.width(), bitmap.height());
  shifted.eraseARGB(0, 0, 0, 0);

  SkAutoLockPixels lock_bitmap(bitmap);
  SkAutoLockPixels lock_shifted(shifted);

  // Loop through the pixels of the original bitmap.
  for (int y = 0; y < bitmap.height(); ++y) {
    SkPMColor* pixels = bitmap.getAddr32(0, y);
    SkPMColor* tinted_pixels = shifted.getAddr32(0, y);

    (*line_proc)(hsl_shift, pixels, tinted_pixels, bitmap.width());
  }

  return shifted;
}

// static
SkBitmap SkBitmapOperations::CreateTiledBitmap(const SkBitmap& source,
                                               int src_x, int src_y,
                                               int dst_w, int dst_h) {
  DCHECK(source.colorType() == kPMColor_SkColorType);

  SkBitmap cropped;
  cropped.allocN32Pixels(dst_w, dst_h);
  cropped.eraseARGB(0, 0, 0, 0);

  SkAutoLockPixels lock_source(source);
  SkAutoLockPixels lock_cropped(cropped);

  // Loop through the pixels of the original bitmap.
  for (int y = 0; y < dst_h; ++y) {
    int y_pix = (src_y + y) % source.height();
    while (y_pix < 0)
      y_pix += source.height();

    uint32* source_row = source.getAddr32(0, y_pix);
    uint32* dst_row = cropped.getAddr32(0, y);

    for (int x = 0; x < dst_w; ++x) {
      int x_pix = (src_x + x) % source.width();
      while (x_pix < 0)
        x_pix += source.width();

      dst_row[x] = source_row[x_pix];
    }
  }

  return cropped;
}

// static
SkBitmap SkBitmapOperations::DownsampleByTwoUntilSize(const SkBitmap& bitmap,
                                                      int min_w, int min_h) {
  if ((bitmap.width() <= min_w) || (bitmap.height() <= min_h) ||
      (min_w < 0) || (min_h < 0))
    return bitmap;

  // Since bitmaps are refcounted, this copy will be fast.
  SkBitmap current = bitmap;
  while ((current.width() >= min_w * 2) && (current.height() >= min_h * 2) &&
         (current.width() > 1) && (current.height() > 1))
    current = DownsampleByTwo(current);
  return current;
}

// static
SkBitmap SkBitmapOperations::DownsampleByTwo(const SkBitmap& bitmap) {
  // Handle the nop case.
  if ((bitmap.width() <= 1) || (bitmap.height() <= 1))
    return bitmap;

  SkBitmap result;
  result.allocN32Pixels((bitmap.width() + 1) / 2, (bitmap.height() + 1) / 2);

  SkAutoLockPixels lock(bitmap);

  const int resultLastX = result.width() - 1;
  const int srcLastX = bitmap.width() - 1;

  for (int dest_y = 0; dest_y < result.height(); ++dest_y) {
    const int src_y = dest_y << 1;
    const SkPMColor* SK_RESTRICT cur_src0 = bitmap.getAddr32(0, src_y);
    const SkPMColor* SK_RESTRICT cur_src1 = cur_src0;
    if (src_y + 1 < bitmap.height())
      cur_src1 = bitmap.getAddr32(0, src_y + 1);

    SkPMColor* SK_RESTRICT cur_dst = result.getAddr32(0, dest_y);

    for (int dest_x = 0; dest_x <= resultLastX; ++dest_x) {
      // This code is based on downsampleby2_proc32 in SkBitmap.cpp. It is very
      // clever in that it does two channels at once: alpha and green ("ag")
      // and red and blue ("rb"). Each channel gets averaged across 4 pixels
      // to get the result.
      int bump_x = (dest_x << 1) < srcLastX;
      SkPMColor tmp, ag, rb;

      // Top left pixel of the 2x2 block.
      tmp = cur_src0[0];
      ag = (tmp >> 8) & 0xFF00FF;
      rb = tmp & 0xFF00FF;

      // Top right pixel of the 2x2 block.
      tmp = cur_src0[bump_x];
      ag += (tmp >> 8) & 0xFF00FF;
      rb += tmp & 0xFF00FF;

      // Bottom left pixel of the 2x2 block.
      tmp = cur_src1[0];
      ag += (tmp >> 8) & 0xFF00FF;
      rb += tmp & 0xFF00FF;

      // Bottom right pixel of the 2x2 block.
      tmp = cur_src1[bump_x];
      ag += (tmp >> 8) & 0xFF00FF;
      rb += tmp & 0xFF00FF;

      // Put the channels back together, dividing each by 4 to get the average.
      // |ag| has the alpha and green channels shifted right by 8 bits from
      // there they should end up, so shifting left by 6 gives them in the
      // correct position divided by 4.
      *cur_dst++ = ((rb >> 2) & 0xFF00FF) | ((ag << 6) & 0xFF00FF00);

      cur_src0 += 2;
      cur_src1 += 2;
    }
  }

  return result;
}

// static
SkBitmap SkBitmapOperations::UnPreMultiply(const SkBitmap& bitmap) {
  if (bitmap.isNull())
    return bitmap;
  if (bitmap.isOpaque())
    return bitmap;

  SkImageInfo info = bitmap.info();
  info.fAlphaType = kOpaque_SkAlphaType;
  SkBitmap opaque_bitmap;
  opaque_bitmap.allocPixels(info);

  {
    SkAutoLockPixels bitmap_lock(bitmap);
    SkAutoLockPixels opaque_bitmap_lock(opaque_bitmap);
    for (int y = 0; y < opaque_bitmap.height(); y++) {
      for (int x = 0; x < opaque_bitmap.width(); x++) {
        uint32 src_pixel = *bitmap.getAddr32(x, y);
        uint32* dst_pixel = opaque_bitmap.getAddr32(x, y);
        SkColor unmultiplied = SkUnPreMultiply::PMColorToColor(src_pixel);
        *dst_pixel = unmultiplied;
      }
    }
  }

  return opaque_bitmap;
}

// static
SkBitmap SkBitmapOperations::CreateTransposedBitmap(const SkBitmap& image) {
  DCHECK(image.colorType() == kPMColor_SkColorType);

  SkBitmap transposed;
  transposed.allocN32Pixels(image.height(), image.width());

  SkAutoLockPixels lock_image(image);
  SkAutoLockPixels lock_transposed(transposed);

  for (int y = 0; y < image.height(); ++y) {
    uint32* image_row = image.getAddr32(0, y);
    for (int x = 0; x < image.width(); ++x) {
      uint32* dst = transposed.getAddr32(y, x);
      *dst = image_row[x];
    }
  }

  return transposed;
}

// static
SkBitmap SkBitmapOperations::CreateColorMask(const SkBitmap& bitmap,
                                             SkColor c) {
  DCHECK(bitmap.colorType() == kPMColor_SkColorType);

  SkBitmap color_mask;
  color_mask.allocN32Pixels(bitmap.width(), bitmap.height());
  color_mask.eraseARGB(0, 0, 0, 0);

  SkCanvas canvas(color_mask);

  skia::RefPtr<SkColorFilter> color_filter = skia::AdoptRef(
      SkColorFilter::CreateModeFilter(c, SkXfermode::kSrcIn_Mode));
  SkPaint paint;
  paint.setColorFilter(color_filter.get());
  canvas.drawBitmap(bitmap, SkIntToScalar(0), SkIntToScalar(0), &paint);
  return color_mask;
}

// static
SkBitmap SkBitmapOperations::CreateDropShadow(
    const SkBitmap& bitmap,
    const gfx::ShadowValues& shadows) {
  DCHECK(bitmap.colorType() == kPMColor_SkColorType);

  // Shadow margin insets are negative values because they grow outside.
  // Negate them here as grow direction is not important and only pixel value
  // is of interest here.
  gfx::Insets shadow_margin = -gfx::ShadowValue::GetMargin(shadows);

  SkBitmap image_with_shadow;
  image_with_shadow.allocN32Pixels(bitmap.width() + shadow_margin.width(),
                                   bitmap.height() + shadow_margin.height());
  image_with_shadow.eraseARGB(0, 0, 0, 0);

  SkCanvas canvas(image_with_shadow);
  canvas.translate(SkIntToScalar(shadow_margin.left()),
                   SkIntToScalar(shadow_margin.top()));

  SkPaint paint;
  for (size_t i = 0; i < shadows.size(); ++i) {
    const gfx::ShadowValue& shadow = shadows[i];
    SkBitmap shadow_image = SkBitmapOperations::CreateColorMask(bitmap,
                                                                shadow.color());

    skia::RefPtr<SkBlurImageFilter> filter =
        skia::AdoptRef(new SkBlurImageFilter(SkDoubleToScalar(shadow.blur()),
                                             SkDoubleToScalar(shadow.blur())));
    paint.setImageFilter(filter.get());

    canvas.saveLayer(0, &paint);
    canvas.drawBitmap(shadow_image,
                      SkIntToScalar(shadow.x()),
                      SkIntToScalar(shadow.y()));
    canvas.restore();
  }

  canvas.drawBitmap(bitmap, SkIntToScalar(0), SkIntToScalar(0));
  return image_with_shadow;
}

// static
SkBitmap SkBitmapOperations::Rotate(const SkBitmap& source,
                                    RotationAmount rotation) {
  SkBitmap result;
  SkScalar angle = SkFloatToScalar(0.0f);

  switch (rotation) {
   case ROTATION_90_CW:
     angle = SkFloatToScalar(90.0f);
     result.setConfig(
         SkBitmap::kARGB_8888_Config, source.height(), source.width());
     break;
   case ROTATION_180_CW:
     angle = SkFloatToScalar(180.0f);
     result.setConfig(
         SkBitmap::kARGB_8888_Config, source.width(), source.height());
     break;
   case ROTATION_270_CW:
     angle = SkFloatToScalar(270.0f);
     result.setConfig(
         SkBitmap::kARGB_8888_Config, source.height(), source.width());
     break;
  }
  result.allocPixels();
  SkCanvas canvas(result);
  canvas.clear(SkColorSetARGB(0, 0, 0, 0));

  canvas.translate(SkFloatToScalar(result.width() * 0.5f),
                   SkFloatToScalar(result.height() * 0.5f));
  canvas.rotate(angle);
  canvas.translate(-SkFloatToScalar(source.width() * 0.5f),
                   -SkFloatToScalar(source.height() * 0.5f));
  canvas.drawBitmap(source, 0, 0);
  canvas.flush();

  return result;
}