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[devel] Use fast integer PNG_DIVIDE_BY_255() or PNG_DIVIDE_BY_65535()

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to accomplish alpha premultiplication when PNG_READ_COMPOSITE_NODIV_SUPPORTED
is defined.  Changed "/255" to "/255.0" in background calculations to make it
clear that the 255 is used as a double (and to prevent anyone from being
tempted to use PNG_DIVIDE_BY_255() there).
This commit is contained in:
Glenn Randers-Pehrson
2009-11-24 07:26:06 -06:00
parent 2a087220dd
commit 768429bbc1
4 changed files with 54 additions and 29 deletions
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43
pngrtran.c
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@@ -1,7 +1,7 @@
/* pngrtran.c - transforms the data in a row for PNG readers
*
* Last changed in libpng 1.4.0 [November 22, 2009]
* Last changed in libpng 1.4.0 [November 24, 2009]
* Copyright (c) 1998-2009 Glenn Randers-Pehrson
* (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
* (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -957,19 +957,19 @@ png_init_read_transformations(png_structp png_ptr)
else
{
back.red = (png_byte)(pow(
(double)png_ptr->background.red/255, gs) * 255.0 + .5);
(double)png_ptr->background.red/255.0, gs) * 255.0 + .5);
back.green = (png_byte)(pow(
(double)png_ptr->background.green/255, gs) * 255.0 + .5);
(double)png_ptr->background.green/255.0, gs) * 255.0 + .5);
back.blue = (png_byte)(pow(
(double)png_ptr->background.blue/255, gs) * 255.0 + .5);
(double)png_ptr->background.blue/255.0, gs) * 255.0 + .5);
}
back_1.red = (png_byte)(pow(
(double)png_ptr->background.red/255, g) * 255.0 + .5);
(double)png_ptr->background.red/255.0, g) * 255.0 + .5);
back_1.green = (png_byte)(pow(
(double)png_ptr->background.green/255, g) * 255.0 + .5);
(double)png_ptr->background.green/255.0, g) * 255.0 + .5);
back_1.blue = (png_byte)(pow(
(double)png_ptr->background.blue/255, g) * 255.0 + .5);
(double)png_ptr->background.blue/255.0, g) * 255.0 + .5);
}
for (i = 0; i < num_palette; i++)
{
@@ -2015,16 +2015,15 @@ png_do_read_premultiply_alpha(png_row_infop row_info, png_bytep row)
{
png_bytep sp = row + row_info->rowbytes;
png_bytep dp = sp;
png_uint_16 a = 0;
png_uint_16 a = 0;
png_uint_32 i;
for (i = 0; i < row_width; i++)
{
a = *(--sp); --dp;
*(--dp) = (*(--sp) * a) / 255;
*(--dp) = (*(--sp) * a) / 255;
*(--dp) = (*(--sp) * a) / 255;
a = *(--sp); --dp;
sp--; *(--dp) = PNG_8_BIT_PREMULTIPLY((*sp), a);
sp--; *(--dp) = PNG_8_BIT_PREMULTIPLY((*sp), a);
sp--; *(--dp) = PNG_8_BIT_PREMULTIPLY((*sp), a);
}
}
/* This premultiplies the pixels with the alpha channel in RRGGBBAA */
@@ -2032,15 +2031,15 @@ png_do_read_premultiply_alpha(png_row_infop row_info, png_bytep row)
{
png_uint_16p sp = (png_uint_16p)(row + row_info->rowbytes);
png_uint_16p dp = sp;
png_uint_32 a = 0;
png_uint_32 a = 0;
png_uint_32 i;
for (i = 0; i < row_width; i++)
{
a = *(--sp); --dp;
*(--dp) = (png_uint_16) ((*(--sp) * a) / 65535);
*(--dp) = (png_uint_16) ((*(--sp) * a) / 65535);
*(--dp) = (png_uint_16) ((*(--sp) * a) / 65535);
a = *(--sp); --dp;
sp--; *(--dp) = PNG_16_BIT_PREMULTIPLY((*sp), a);
sp--; *(--dp) = PNG_16_BIT_PREMULTIPLY((*sp), a);
sp--; *(--dp) = PNG_16_BIT_PREMULTIPLY((*sp), a);
}
}
}
@@ -2052,12 +2051,12 @@ png_do_read_premultiply_alpha(png_row_infop row_info, png_bytep row)
png_bytep sp = row + row_info->rowbytes;
png_bytep dp = sp;
png_uint_16 a = 0;
png_uint_32 i;
png_uint_32 i;
for (i = 0; i < row_width; i++)
{
a = *(--sp); --dp;
*(--dp) = (*(--sp) * a) / 255;
sp--; *(--dp) = PNG_8_BIT_PREMULTIPLY((*sp), a);
}
}
/* This premultiplies the pixels with the alpha channel in GGAA */
@@ -2070,8 +2069,8 @@ png_do_read_premultiply_alpha(png_row_infop row_info, png_bytep row)
for (i = 0; i < row_width; i++)
{
a = *(--sp); --dp;
*(--dp) = (png_uint_16) ((*(--sp) * a) / 65535);
a = *(--sp); --dp;
sp--; *(--dp) = PNG_16_BIT_PREMULTIPLY((*sp), a);
}
}
}