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[libpng16] Support associated alpha in the simplified api

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This commit is contained in:
Glenn Randers-Pehrson 2017-09-23 14:53:44 -05:00
commit 4b7635ce72
2 changed files with 13 additions and 1 deletions
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2
png.h
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@ -2819,6 +2819,8 @@ typedef struct
# define PNG_FORMAT_FLAG_AFIRST 0x20U /* alpha channel comes first */
#endif
#define PNG_FORMAT_FLAG_ASSOCIATED_ALPHA 0x40U /* alpha channel is associated */
/* Commonly used formats have predefined macros.
*
* First the single byte (sRGB) formats:

12
pngread.c
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@ -3759,7 +3759,13 @@ png_image_read_direct(png_voidp argument)
mode = PNG_ALPHA_PNG;
output_gamma = PNG_DEFAULT_sRGB;
}
if ((change & PNG_FORMAT_FLAG_ASSOCIATED_ALPHA) != 0)
{
mode = PNG_ALPHA_OPTIMIZED;
change &= ~PNG_FORMAT_FLAG_ASSOCIATED_ALPHA;
}
/* If 'do_local_background' is set check for the presence of gamma
* correction; this is part of the work-round for the libpng bug
* described above.
@ -3985,6 +3991,10 @@ png_image_read_direct(png_voidp argument)
else if (do_local_compose != 0) /* internal error */
png_error(png_ptr, "png_image_read: alpha channel lost");
if ((format & PNG_FORMAT_FLAG_ASSOCIATED_ALPHA) != 0) {
info_format |= PNG_FORMAT_FLAG_ASSOCIATED_ALPHA;
}
if (info_ptr->bit_depth == 16)
info_format |= PNG_FORMAT_FLAG_LINEAR;