text: /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
   * ***** 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 gfx thebes code.
   *
   * The Initial Developer of the Original Code is Mozilla Foundation.
   * Portions created by the Initial Developer are Copyright (C) 2008
   * the Initial Developer. All Rights Reserved.
   *
   * Contributor(s):
   *   Eric Butler <zantifon@gmail.com>
   *
   * 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
   * under the terms of either the GPL or the LGPL, and not to allow others to
   * use your version of this file under the terms of the MPL, indicate your
   * 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 GFX_BLUR_H
  #define GFX_BLUR_H
  
  #include "gfxContext.h"
  #include "gfxImageSurface.h"
  #include "gfxTypes.h"
  #include "gfxUtils.h"
  #include "nsRect.h"
  
  /**
   * 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 THEBES_API 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 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.
       */
      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, const gfxPoint& offset = gfxPoint(0.0, 0.0));
  
      /**
       * 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);
  
  protected:
      /**
       * The spread radius, in pixels.
       */
      gfxIntSize mSpreadRadius;
      /**
       * The blur radius, in pixels.
       */
      gfxIntSize mBlurRadius;
  
      /**
       * The context of the temporary alpha surface.
       */
      nsRefPtr<gfxContext> mContext;
  
      /**
       * The temporary alpha surface.
       */
      nsRefPtr<gfxImageSurface> mImageSurface;
  
      /**
       * A copy of the dirty rect passed to Init(). This will only be valid if
       * mHasDirtyRect is TRUE.
       */
      gfxRect mDirtyRect;
      /**
       * A rect indicating the area where blurring is unnecessary, and the blur
       * algorithm should skip over it.
       */
      nsIntRect mSkipRect;
  
      PRPackedBool mHasDirtyRect;
  };
  
  #endif /* GFX_BLUR_H */
  