diff options
Diffstat (limited to 'src/base/ftbitmap.c')
| -rw-r--r-- | src/base/ftbitmap.c | 45 |
1 files changed, 17 insertions, 28 deletions
diff --git a/src/base/ftbitmap.c b/src/base/ftbitmap.c index 182b1cc..6542c79 100644 --- a/src/base/ftbitmap.c +++ b/src/base/ftbitmap.c @@ -4,7 +4,7 @@ /* */ /* FreeType utility functions for bitmaps (body). */ /* */ -/* Copyright 2004-2009, 2011, 2013 by */ +/* Copyright 2004-2009, 2011, 2013, 2014 by */ /* David Turner, Robert Wilhelm, and Werner Lemberg. */ /* */ /* This file is part of the FreeType project, and may only be used, */ @@ -375,14 +375,11 @@ } - FT_Byte + static FT_Byte ft_gray_for_premultiplied_srgb_bgra( const FT_Byte* bgra ) { - FT_Long a = bgra[3]; - FT_Long b = bgra[0]; - FT_Long g = bgra[1]; - FT_Long r = bgra[2]; - FT_Long l; + FT_Byte a = bgra[3]; + FT_ULong l; /* Short-circuit transparent color to avoid div-by-zero. */ @@ -397,38 +394,30 @@ * * http://accessibility.kde.org/hsl-adjusted.php * - * We do the computation with integers only. + * 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. + * */ - /* Undo premultification, get the number in a 16.16 form. */ - b = FT_MulDiv( b, 65536, a ); - g = FT_MulDiv( g, 65536, a ); - r = FT_MulDiv( r, 65536, a ); - a = a * 256; - - /* Apply gamma of 2.0 instead of 2.2. */ - b = FT_MulFix( b, b ); - g = FT_MulFix( g, g ); - r = FT_MulFix( r, r ); - - /* Apply coefficients. */ - b = FT_MulFix( b, 4731 /* 0.0722 * 65536 */ ); - g = FT_MulFix( g, 46871 /* 0.7152 * 65536 */ ); - r = FT_MulFix( r, 13933 /* 0.2126 * 65536 */ ); - - l = r + g + b; + 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]; /* - * Final transparency can be determined this way: + * Final transparency can be determined as follows. * * - If alpha is zero, we want 0. * - If alpha is zero and luminosity is zero, we want 255. * - If alpha is zero and luminosity is one, we want 0. * - * So the formula is a * (1 - l). + * So the formula is a * (1 - l) = a - l * a. + * + * In the actual code, we undo premultiplication and scale down again. + * */ - return (FT_Byte)( FT_MulFix( 65535 - l, a ) >> 8 ); + return a - (FT_Byte)( ( l / a ) >> 16 ); } |