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 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-

  * 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 GFX_BLUR_H

 #define GFX_BLUR_H

 #include "gfxTypes.h"

 #include "nsSize.h"

 #include "nsAutoPtr.h"

 #include "gfxPoint.h"

 #include "mozilla/RefPtr.h"

 class gfxContext;

 struct gfxRect;

 struct gfxRGBA;

 class gfxCornerSizes;

 class gfxMatrix;

 namespace mozilla {

   namespace gfx {

     class AlphaBoxBlur;

     class SourceSurface;

     class DrawTarget;

   }

 }

 /**

  * 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, blurs the contents, and applies

  * it as an alpha mask on a different existing context.

  * 

  * 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 gfxAlphaBoxBlur

 {

 public:

     gfxAlphaBoxBlur();

     ~gfxAlphaBoxBlur();

     /**

      * Constructs a box blur and initializes the temporary 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.

      */

     gfxContext* Init(const gfxRect& aRect,

                      const gfxIntSize& aSpreadRadius,

                      const gfxIntSize& aBlurRadius,

                      const gfxRect* aDirtyRect,

                      const gfxRect* aSkipRect);

     /**

      * Returns the context that should be drawn to supply the alpha mask to be

      * blurred. If the returned surface is null, then there was an error in

      * its creation.

      */

     gfxContext* GetContext()

     {

         return mContext;

     }

     /**

      * Does the actual blurring/spreading and mask applying. Users of this

      * object must have drawn whatever they want to be blurred onto the internal

      * gfxContext returned by GetContext before calling this.

      *

      * @param aDestinationCtx The graphics context on which to apply the

      *  blurred mask.

      */

     void Paint(gfxContext* aDestinationCtx);

     /**

      * 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 Init,

      * above.

      */

     static gfxIntSize CalculateBlurRadius(const gfxPoint& aStandardDeviation);

     /**

      * Blurs a coloured rectangle onto aDestinationCtx. This is equivalent

      * to calling Init(), drawing a rectangle onto the returned surface

      * and then calling Paint, but may let us optimize better in the

      * backend.

      *

      * @param aDestinationCtx      The destination to blur to.

      * @param aRect                The rectangle to blur in device pixels.

      * @param aCornerRadii         Corner radii for aRect, if it is a rounded

      *                             rectangle.

      * @param aBlurRadius          The standard deviation of the blur.

      * @param aShadowColor         The color to draw the blurred shadow.

      * @param aDirtyRect           An area in device pixels that is dirty and needs

      *                             to be redrawn.

      * @param aSkipRect            An area in device pixels to avoid blurring over,

      *                             to prevent unnecessary work.

      */

     static void BlurRectangle(gfxContext *aDestinationCtx,

                               const gfxRect& aRect,

                               gfxCornerSizes* aCornerRadii,

                               const gfxPoint& aBlurStdDev,

                               const gfxRGBA& aShadowColor,

                               const gfxRect& aDirtyRect,

                               const gfxRect& aSkipRect);

 protected:

     /**

      * The context of the temporary alpha surface.

      */

     nsRefPtr<gfxContext> mContext;

     /**

      * The temporary alpha surface.

      */

     nsAutoArrayPtr<unsigned char> mData;

      /**

       * The object that actually does the blurring for us.

       */

     mozilla::gfx::AlphaBoxBlur *mBlur;

 };

 #endif /* GFX_BLUR_H */