gecko-dev/gfx/2d/Blur.h

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/* ***** BEGIN LICENSE BLOCK *****
* Version: MPL 1.1/GPL 2.0/LGPL 2.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*
* The Original Code is Mozilla gfx.
*
* The Initial Developer of the Original Code is Mozilla Foundation.
* Portions created by the Initial Developer are Copyright (C) 2011
* the Initial Developer. All Rights Reserved.
*
* Contributor(s):
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU General Public License Version 2 or later (the "GPL"), or
* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
* in which case the provisions of the GPL or the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
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* decision by deleting the provisions above and replace them with the notice
* and other provisions required by the GPL or the LGPL. If you do not delete
* the provisions above, a recipient may use your version of this file under
* the terms of any one of the MPL, the GPL or the LGPL.
*
* ***** END LICENSE BLOCK ***** */
#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 NULL 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 NULL 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 NULL
* 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_ */