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* src/base/ftbitmap.c (ft_gray_for_premultiplied_srgb_bgra): Refactor.

This commit is contained in:
Alexei Podtelezhnikov 2014-08-08 22:27:10 -04:00
parent e1394d5675
commit 90be4b6377
2 changed files with 13 additions and 9 deletions
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4
ChangeLog
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@ -1,3 +1,7 @@
2014-08-08 Alexei Podtelezhnikov <apodtele@gmail.com>
* src/base/ftbitmap.c (ft_gray_for_premultiplied_srgb_bgra): Refactor.
2014-07-26 Werner Lemberg <wl@gnu.org>
[cff] Fix typo.

18
src/base/ftbitmap.c
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@ -378,8 +378,8 @@
static FT_Byte
ft_gray_for_premultiplied_srgb_bgra( const FT_Byte* bgra )
{
FT_Byte a = bgra[3];
FT_ULong l;
FT_UInt a = bgra[3];
FT_UInt l;
/* Short-circuit transparent color to avoid div-by-zero. */
@ -395,14 +395,14 @@
* http://accessibility.kde.org/hsl-adjusted.php
*
* We do the computation with integers only, applying a gamma of 2.0.
* The following will never overflow 32 bits; it is a scaled-up
* luminosity with premultiplication not yet undone.
* We guarantee 32-bit arithmetic to avoid overflow but the resulting
* luminosity fits into 16 bits.
*
*/
l = 4731UL /* 0.0722 * 65536 */ * bgra[0] * bgra[0] +
46871UL /* 0.7152 * 65536 */ * bgra[1] * bgra[1] +
13933UL /* 0.2126 * 65536 */ * bgra[2] * bgra[2];
l = ( 4732UL /* 0.0722 * 65536 */ * bgra[0] * bgra[0] +
46871UL /* 0.7152 * 65536 */ * bgra[1] * bgra[1] +
13933UL /* 0.2126 * 65536 */ * bgra[2] * bgra[2] ) >> 16;
/*
* Final transparency can be determined as follows.
@ -413,11 +413,11 @@
*
* So the formula is a * (1 - l) = a - l * a.
*
* In the actual code, we undo premultiplication and scale down again.
* We still need to undo premultiplication by dividing l by a*a.
*
*/
return a - (FT_Byte)( ( l / a ) >> 16 );
return (FT_Byte)( a - l / a );
}