DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Implementation

Mercurial (5b81998bb7ab)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef MOZILLA_GFX_BLUR_H_
#define MOZILLA_GFX_BLUR_H_

#include "mozilla/gfx/Rect.h"
#include "mozilla/gfx/Point.h"

namespace mozilla {
namespace gfx {

/**
 * Implementation of a triple box blur approximation of a Gaussian blur.
 *
 * A Gaussian blur is good for blurring because, when done independently
 * in the horizontal and vertical directions, it matches the result that
 * would be obtained using a different (rotated) set of axes.  A triple
 * box blur is a very close approximation of a Gaussian.
 *
 * Creates an 8-bit alpha channel context for callers to draw in,
 * spreads the contents of that context, and blurs the contents.
 *
 * A spread N makes each output pixel the maximum value of all source
 * pixels within a square of side length 2N+1 centered on the output pixel.
 *
 * A temporary surface is created in the Init function. The caller then draws
 * any desired content onto the context acquired through GetContext, and lastly
 * calls Paint to apply the blurred content as an alpha mask.
 */
class GFX2D_API AlphaBoxBlur
{
public:

  /** Constructs a box blur and initializes the backing surface.
   *
   * @param aRect The coordinates of the surface to create in device units.
   *
   * @param aBlurRadius The blur radius in pixels.  This is the radius of the
   *   entire (triple) kernel function.  Each individual box blur has radius
   *   approximately 1/3 this value, or diameter approximately 2/3 this value.
   *   This parameter should nearly always be computed using CalculateBlurRadius,
   *   below.
   *
   * @param aDirtyRect A pointer to a dirty rect, measured in device units, if
   *   available.  This will be used for optimizing the blur operation. It is
   *   safe to pass nullptr here.
   *
   * @param aSkipRect A pointer to a rect, measured in device units, that
   *   represents an area where blurring is unnecessary and shouldn't be done for
   *   speed reasons. It is safe to pass nullptr here.
   */
  AlphaBoxBlur(const Rect& aRect,
               const IntSize& aSpreadRadius,
               const IntSize& aBlurRadius,
               const Rect* aDirtyRect,
               const Rect* aSkipRect);

  ~AlphaBoxBlur();

  /**
   * Return the pointer to memory allocated by the constructor for the 8-bit
   * alpha surface you need to be blurred. After you draw to this surface, call
   * Blur(), below, to have its contents blurred.
   */
  unsigned char* GetData();

  /**
   * Return the size, in pixels, of the 8-bit alpha surface backed by the
   * pointer returned by GetData().
   */
  IntSize GetSize();

  /**
   * Return the stride, in bytes, of the 8-bit alpha surface backed by the
   * pointer returned by GetData().
   */
  int32_t GetStride();

  /**
   * Returns the device-space rectangle the 8-bit alpha surface covers.
   */
  IntRect GetRect();

  /**
   * Return a pointer to a dirty rect, as passed in to the constructor, or nullptr
   * if none was passed in.
   */
  Rect* GetDirtyRect();

  /**
   * Perform the blur in-place on the surface backed by the pointer returned by
   * GetData().
   */
  void Blur();

  /**
   * Calculates a blur radius that, when used with box blur, approximates a
   * Gaussian blur with the given standard deviation.  The result of this
   * function should be used as the aBlurRadius parameter to AlphaBoxBlur's
   * constructor, above.
   */
  static IntSize CalculateBlurRadius(const Point& aStandardDeviation);

private:

  /**
   * A rect indicating the area where blurring is unnecessary, and the blur
   * algorithm should skip over it.
   */
  IntRect mSkipRect;

  /**
   * The device-space rectangle the the backing 8-bit alpha surface covers.
   */
  IntRect mRect;

  /**
   * A copy of the dirty rect passed to the constructor. This will only be valid if
   * mHasDirtyRect is true.
   */
  Rect mDirtyRect;

  /**
   * The spread radius, in pixels.
   */
  IntSize mSpreadRadius;

  /**
   * The blur radius, in pixels.
   */
  IntSize mBlurRadius;

  /**
   * A pointer to the backing 8-bit alpha surface.
   */
  unsigned char* mData;

  /**
   * The stride of the data contained in mData.
   */
  int32_t mStride;

  /**
   * Whether mDirtyRect contains valid data.
   */
  bool mHasDirtyRect;
};

}
}

#endif /* MOZILLA_GFX_BLUR_H_ */