LCOV - code coverage report
Current view: directory - gfx/thebes - gfxAlphaRecovery.h (source / functions) Found Hit Coverage
Test: app.info Lines: 8 1 12.5 %
Date: 2012-06-02 Functions: 2 1 50.0 %

       1                 : /* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
       2                 :  * ***** BEGIN LICENSE BLOCK *****
       3                 :  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
       4                 :  *
       5                 :  * The contents of this file are subject to the Mozilla Public License Version
       6                 :  * 1.1 (the "License"); you may not use this file except in compliance with
       7                 :  * the License. You may obtain a copy of the License at
       8                 :  * http://www.mozilla.org/MPL/
       9                 :  *
      10                 :  * Software distributed under the License is distributed on an "AS IS" basis,
      11                 :  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
      12                 :  * for the specific language governing rights and limitations under the
      13                 :  * License.
      14                 :  *
      15                 :  * The Original Code is Thebes gfx.
      16                 :  *
      17                 :  * The Initial Developer of the Original Code is Mozilla Foundation.
      18                 :  * Portions created by the Initial Developer are Copyright (C) 2007
      19                 :  * the Initial Developer. All Rights Reserved.
      20                 :  *
      21                 :  * Contributor(s):
      22                 :  *   Vladimir Vukicevic <vladimir@pobox.com>
      23                 :  *
      24                 :  * Alternatively, the contents of this file may be used under the terms of
      25                 :  * either the GNU General Public License Version 2 or later (the "GPL"), or
      26                 :  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
      27                 :  * in which case the provisions of the GPL or the LGPL are applicable instead
      28                 :  * of those above. If you wish to allow use of your version of this file only
      29                 :  * under the terms of either the GPL or the LGPL, and not to allow others to
      30                 :  * use your version of this file under the terms of the MPL, indicate your
      31                 :  * decision by deleting the provisions above and replace them with the notice
      32                 :  * and other provisions required by the GPL or the LGPL. If you do not delete
      33                 :  * the provisions above, a recipient may use your version of this file under
      34                 :  * the terms of any one of the MPL, the GPL or the LGPL.
      35                 :  *
      36                 :  * ***** END LICENSE BLOCK ***** */
      37                 : 
      38                 : #ifndef _GFXALPHARECOVERY_H_
      39                 : #define _GFXALPHARECOVERY_H_
      40                 : 
      41                 : #include "gfxContext.h"
      42                 : #include "gfxImageSurface.h"
      43                 : #include "mozilla/SSE.h"
      44                 : #include "nsRect.h"
      45                 : 
      46                 : class THEBES_API gfxAlphaRecovery {
      47                 : public:
      48                 :     struct Analysis {
      49                 :         bool uniformColor;
      50                 :         bool uniformAlpha;
      51                 :         gfxFloat alpha;
      52                 :         gfxFloat r, g, b;
      53                 :     };
      54                 : 
      55                 :     /**
      56                 :      * Some SIMD fast-paths only can be taken if the relative
      57                 :      * byte-alignment of images' pointers and strides meets certain
      58                 :      * criteria.  Aligning image pointers and strides by
      59                 :      * |GoodAlignmentLog2()| below will ensure that fast-paths aren't
      60                 :      * skipped because of misalignment.  Fast-paths may still be taken
      61                 :      * even if GoodAlignmentLog2() is not met, in some conditions.
      62                 :      */
      63              65 :     static PRUint32 GoodAlignmentLog2() { return 4; /* for SSE2 */ }
      64                 : 
      65                 :     /* Given two surfaces of equal size with the same rendering, one onto a
      66                 :      * black background and the other onto white, recovers alpha values from
      67                 :      * the difference and sets the alpha values on the black surface.
      68                 :      * The surfaces must have format RGB24 or ARGB32.
      69                 :      * Returns true on success.
      70                 :      */
      71                 :     static bool RecoverAlpha (gfxImageSurface *blackSurface,
      72                 :                                 const gfxImageSurface *whiteSurface,
      73                 :                                 Analysis *analysis = nsnull);
      74                 : 
      75                 : #ifdef MOZILLA_MAY_SUPPORT_SSE2
      76                 :     /* This does the same as the previous function, but uses SSE2
      77                 :      * optimizations. Usually this should not be called directly.  Be sure to
      78                 :      * check mozilla::supports_sse2() before calling this function.
      79                 :      */
      80                 :     static bool RecoverAlphaSSE2 (gfxImageSurface *blackSurface,
      81                 :                                     const gfxImageSurface *whiteSurface);
      82                 : 
      83                 :     /**
      84                 :      * A common use-case for alpha recovery is to paint into a
      85                 :      * temporary "white image", then paint onto a subrect of the
      86                 :      * surface, the "black image", into which alpha-recovered pixels
      87                 :      * are eventually to be written.  This function returns a rect
      88                 :      * aligned so that recovering alpha for that rect will hit SIMD
      89                 :      * fast-paths, if possible.  It's not always possible to align
      90                 :      * |aRect| so that fast-paths will be taken.
      91                 :      *
      92                 :      * The returned rect is always a superset of |aRect|.
      93                 :      */
      94                 :     static nsIntRect AlignRectForSubimageRecovery(const nsIntRect& aRect,
      95                 :                                                   gfxImageSurface* aSurface);
      96                 : #else
      97                 :     static nsIntRect AlignRectForSubimageRecovery(const nsIntRect& aRect,
      98                 :                                                   gfxImageSurface*)
      99                 :     { return aRect; }
     100                 : #endif
     101                 : 
     102                 :     /** from cairo-xlib-utils.c, modified */
     103                 :     /**
     104                 :      * Given the RGB data for two image surfaces, one a source image composited
     105                 :      * with OVER onto a black background, and one a source image composited with 
     106                 :      * OVER onto a white background, reconstruct the original image data into
     107                 :      * black_data.
     108                 :      *
     109                 :      * Consider a single color channel and a given pixel. Suppose the original
     110                 :      * premultiplied color value was C and the alpha value was A. Let the final
     111                 :      * on-black color be B and the final on-white color be W. All values range
     112                 :      * over 0-255.
     113                 :      *
     114                 :      * Then B=C and W=(255*(255 - A) + C*255)/255. Solving for A, we get
     115                 :      * A=255 - (W - C). Therefore it suffices to leave the black_data color
     116                 :      * data alone and set the alpha values using that simple formula. It shouldn't
     117                 :      * matter what color channel we pick for the alpha computation, but we'll
     118                 :      * pick green because if we went through a color channel downsample the green
     119                 :      * bits are likely to be the most accurate.
     120                 :      *
     121                 :      * This function needs to be in the header file since it's used by both
     122                 :      * gfxRecoverAlpha.cpp and gfxRecoverAlphaSSE2.cpp.
     123                 :      */
     124                 : 
     125                 :     static inline PRUint32
     126               0 :     RecoverPixel(PRUint32 black, PRUint32 white)
     127                 :     {
     128               0 :         const PRUint32 GREEN_MASK = 0x0000FF00;
     129               0 :         const PRUint32 ALPHA_MASK = 0xFF000000;
     130                 : 
     131                 :         /* |diff| here is larger when the source image pixel is more transparent.
     132                 :            If both renderings are from the same source image composited with OVER,
     133                 :            then the color values on white will always be greater than those on
     134                 :            black, so |diff| would not overflow.  However, overflow may happen, for
     135                 :            example, when a plugin plays a video and the image is rapidly changing.
     136                 :            If there is overflow, then behave as if we limit to the difference to
     137                 :            >= 0, which will make the rendering opaque.  (Without this overflow
     138                 :            will make the rendering transparent.) */
     139               0 :         PRUint32 diff = (white & GREEN_MASK) - (black & GREEN_MASK);
     140                 :         /* |diff| is 0xFFFFxx00 on overflow and 0x0000xx00 otherwise, so use this
     141                 :             to limit the transparency. */
     142               0 :         PRUint32 limit = diff & ALPHA_MASK;
     143                 :         /* The alpha bits of the result */
     144               0 :         PRUint32 alpha = (ALPHA_MASK - (diff << 16)) | limit;
     145                 : 
     146               0 :         return alpha | (black & ~ALPHA_MASK);
     147                 :     }
     148                 : };
     149                 : 
     150                 : #endif /* _GFXALPHARECOVERY_H_ */

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