mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-23 21:01:08 +00:00
fd7b78a368
Depends on D196459 Differential Revision: https://phabricator.services.mozilla.com/D196860
90 lines
3.8 KiB
C++
90 lines
3.8 KiB
C++
/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
|
|
* 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 _GFXALPHARECOVERY_H_
|
|
#define _GFXALPHARECOVERY_H_
|
|
|
|
#include "gfxTypes.h"
|
|
#include "mozilla/gfx/Rect.h"
|
|
|
|
class gfxImageSurface;
|
|
|
|
class gfxAlphaRecovery {
|
|
public:
|
|
/**
|
|
* Some SIMD fast-paths only can be taken if the relative
|
|
* byte-alignment of images' pointers and strides meets certain
|
|
* criteria. Aligning image pointers and strides by
|
|
* |GoodAlignmentLog2()| below will ensure that fast-paths aren't
|
|
* skipped because of misalignment. Fast-paths may still be taken
|
|
* even if GoodAlignmentLog2() is not met, in some conditions.
|
|
*/
|
|
static uint32_t GoodAlignmentLog2() { return 4; /* for SSE2 */ }
|
|
|
|
/* Given two surfaces of equal size with the same rendering, one onto a
|
|
* black background and the other onto white, recovers alpha values from
|
|
* the difference and sets the alpha values on the black surface.
|
|
* The surfaces must have format RGB24 or ARGB32.
|
|
* Returns true on success.
|
|
*/
|
|
static bool RecoverAlpha(gfxImageSurface* blackSurface,
|
|
const gfxImageSurface* whiteSurface);
|
|
|
|
/* This does the same as the previous function, but uses SIMD
|
|
* optimizations. Usually this should not be called directly.
|
|
*/
|
|
template <class Arch>
|
|
static bool RecoverAlphaGeneric(gfxImageSurface* blackSurface,
|
|
const gfxImageSurface* whiteSurface);
|
|
|
|
/** from cairo-xlib-utils.c, modified */
|
|
/**
|
|
* Given the RGB data for two image surfaces, one a source image composited
|
|
* with OVER onto a black background, and one a source image composited with
|
|
* OVER onto a white background, reconstruct the original image data into
|
|
* black_data.
|
|
*
|
|
* Consider a single color channel and a given pixel. Suppose the original
|
|
* premultiplied color value was C and the alpha value was A. Let the final
|
|
* on-black color be B and the final on-white color be W. All values range
|
|
* over 0-255.
|
|
*
|
|
* Then B=C and W=(255*(255 - A) + C*255)/255. Solving for A, we get
|
|
* A=255 - (W - C). Therefore it suffices to leave the black_data color
|
|
* data alone and set the alpha values using that simple formula. It shouldn't
|
|
* matter what color channel we pick for the alpha computation, but we'll
|
|
* pick green because if we went through a color channel downsample the green
|
|
* bits are likely to be the most accurate.
|
|
*
|
|
* This function needs to be in the header file since it's used by both
|
|
* gfxRecoverAlpha.cpp and gfxRecoverAlphaGeneric.hpp.
|
|
*/
|
|
|
|
static inline uint32_t RecoverPixel(uint32_t black, uint32_t white) {
|
|
const uint32_t GREEN_MASK = 0x0000FF00;
|
|
const uint32_t ALPHA_MASK = 0xFF000000;
|
|
|
|
/* |diff| here is larger when the source image pixel is more
|
|
transparent. If both renderings are from the same source image
|
|
composited with OVER, then the color values on white will always be
|
|
greater than those on black, so |diff| would not overflow. However,
|
|
overflow may happen, for example, when a plugin plays a video and
|
|
the image is rapidly changing. If there is overflow, then behave as
|
|
if we limit to the difference to
|
|
>= 0, which will make the rendering opaque. (Without this overflow
|
|
will make the rendering transparent.) */
|
|
uint32_t diff = (white & GREEN_MASK) - (black & GREEN_MASK);
|
|
/* |diff| is 0xFFFFxx00 on overflow and 0x0000xx00 otherwise, so use
|
|
this to limit the transparency. */
|
|
uint32_t limit = diff & ALPHA_MASK;
|
|
/* The alpha bits of the result */
|
|
uint32_t alpha = (ALPHA_MASK - (diff << 16)) | limit;
|
|
|
|
return alpha | (black & ~ALPHA_MASK);
|
|
}
|
|
};
|
|
|
|
#endif /* _GFXALPHARECOVERY_H_ */
|