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stb_image_write: Support writing BMPs with alpha

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Fixes issue #1159.
This commit is contained in:
Fabian Giesen 2021-07-07 14:35:46 -07:00
parent 315e979f34
commit b14a80784c
1 changed files with 17 additions and 5 deletions
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22
stb_image_write.h
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@ -491,11 +491,22 @@ static int stbiw__outfile(stbi__write_context *s, int rgb_dir, int vdir, int x,
static int stbi_write_bmp_core(stbi__write_context *s, int x, int y, int comp, const void *data)
{
int pad = (-x*3) & 3;
return stbiw__outfile(s,-1,-1,x,y,comp,1,(void *) data,0,pad,
"11 4 22 4" "4 44 22 444444",
'B', 'M', 14+40+(x*3+pad)*y, 0,0, 14+40, // file header
40, x,y, 1,24, 0,0,0,0,0,0); // bitmap header
if (comp != 4) {
// write RGB bitmap
int pad = (-x*3) & 3;
return stbiw__outfile(s,-1,-1,x,y,comp,1,(void *) data,0,pad,
"11 4 22 4" "4 44 22 444444",
'B', 'M', 14+40+(x*3+pad)*y, 0,0, 14+40, // file header
40, x,y, 1,24, 0,0,0,0,0,0); // bitmap header
} else {
// RGBA bitmaps need a v4 header
// use BI_BITFIELDS mode with 32bpp and alpha mask
// (straight BI_RGB with alpha mask doesn't work in most readers)
return stbiw__outfile(s,-1,-1,x,y,comp,1,(void *)data,1,0,
"11 4 22 4" "4 44 22 444444 4444 4 444 444 444 444",
'B', 'M', 14+108+x*y*4, 0, 0, 14+108, // file header
108, x,y, 1,32, 3,0,0,0,0,0, 0xff0000,0xff00,0xff,0xff000000u, 0, 0,0,0, 0,0,0, 0,0,0, 0,0,0); // bitmap V4 header
}
}
STBIWDEF int stbi_write_bmp_to_func(stbi_write_func *func, void *context, int x, int y, int comp, const void *data)
@ -1619,6 +1630,7 @@ STBIWDEF int stbi_write_jpg(char const *filename, int x, int y, int comp, const
/* Revision history
1.15 ( )
make Deflate code emit uncompressed blocks when it would otherwise expand
support writing BMPs with alpha channel
1.14 (2020-02-02) updated JPEG writer to downsample chroma channels
1.13
1.12