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122 lines
5.3 KiB
C++
122 lines
5.3 KiB
C++
/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is Thebes gfx.
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*
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* The Initial Developer of the Original Code is Mozilla Foundation.
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* Portions created by the Initial Developer are Copyright (C) 2007
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Vladimir Vukicevic <vladimir@pobox.com>
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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#ifndef _GFXALPHARECOVERY_H_
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#define _GFXALPHARECOVERY_H_
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#include "gfxContext.h"
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#include "gfxImageSurface.h"
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#include "mozilla/SSE.h"
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class THEBES_API gfxAlphaRecovery {
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public:
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struct Analysis {
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PRBool uniformColor;
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PRBool uniformAlpha;
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gfxFloat alpha;
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gfxFloat r, g, b;
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};
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/* Given two surfaces of equal size with the same rendering, one onto a
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* black background and the other onto white, recovers alpha values from
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* the difference and sets the alpha values on the black surface.
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* The surfaces must have format RGB24 or ARGB32.
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* Returns PR_TRUE on success.
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*/
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static PRBool RecoverAlpha (gfxImageSurface *blackSurface,
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const gfxImageSurface *whiteSurface,
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Analysis *analysis = nsnull);
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#ifdef MOZILLA_MAY_SUPPORT_SSE2
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/* This does the save as the previous function, but uses SSE2
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* optimizations. Usually this should not be called directly. Be sure to
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* check mozilla::supports_sse2() before calling this function.
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*/
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static PRBool RecoverAlphaSSE2 (gfxImageSurface *blackSurface,
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const gfxImageSurface *whiteSurface);
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#endif
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/** from cairo-xlib-utils.c, modified */
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/**
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* Given the RGB data for two image surfaces, one a source image composited
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* with OVER onto a black background, and one a source image composited with
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* OVER onto a white background, reconstruct the original image data into
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* black_data.
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*
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* Consider a single color channel and a given pixel. Suppose the original
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* premultiplied color value was C and the alpha value was A. Let the final
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* on-black color be B and the final on-white color be W. All values range
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* over 0-255.
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*
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* Then B=C and W=(255*(255 - A) + C*255)/255. Solving for A, we get
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* A=255 - (W - C). Therefore it suffices to leave the black_data color
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* data alone and set the alpha values using that simple formula. It shouldn't
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* matter what color channel we pick for the alpha computation, but we'll
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* pick green because if we went through a color channel downsample the green
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* bits are likely to be the most accurate.
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*
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* This function needs to be in the header file since it's used by both
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* gfxRecoverAlpha.cpp and gfxRecoverAlphaSSE2.cpp.
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*/
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static inline PRUint32
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RecoverPixel(PRUint32 black, PRUint32 white)
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{
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const PRUint32 GREEN_MASK = 0x0000FF00;
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const PRUint32 ALPHA_MASK = 0xFF000000;
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/* |diff| here is larger when the source image pixel is more transparent.
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If both renderings are from the same source image composited with OVER,
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then the color values on white will always be greater than those on
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black, so |diff| would not overflow. However, overflow may happen, for
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example, when a plugin plays a video and the image is rapidly changing.
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If there is overflow, then behave as if we limit to the difference to
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>= 0, which will make the rendering opaque. (Without this overflow
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will make the rendering transparent.) */
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PRUint32 diff = (white & GREEN_MASK) - (black & GREEN_MASK);
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/* |diff| is 0xFFFFxx00 on overflow and 0x0000xx00 otherwise, so use this
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to limit the transparency. */
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PRUint32 limit = diff & ALPHA_MASK;
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/* The alpha bits of the result */
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PRUint32 alpha = (ALPHA_MASK - (diff << 16)) | limit;
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return alpha | (black & ~ALPHA_MASK);
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}
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};
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#endif /* _GFXALPHARECOVERY_H_ */
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