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stb_image: BMP v4/v5 header parsing fixes 

As per MS's own docs, should ignore the r/g/b bitmasks in the
header unless BI_BITFIELDS compression is selected. Factor out
setting the default masks since that now exists in two branches.

Add some more checking for unsupported compression formats and
illegal bpp/compression combinations while I'm at it.

Fixes issue #783.
This commit is contained in:
Fabian Giesen 2021-07-04 22:17:57 -07:00
parent 17bc84e15d
commit 1e82fd4a4e
1 changed files with 32 additions and 11 deletions
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43
stb_image.h
View File

@ -5320,6 +5320,32 @@ typedef struct
int extra_read;
} stbi__bmp_data;
static int stbi__bmp_set_mask_defaults(stbi__bmp_data *info, int compress)
{
// BI_BITFIELDS specifies masks explicitly, don't override
if (compress == 3)
return 1;
if (compress == 0) {
if (info->bpp == 16) {
info->mr = 31u << 10;
info->mg = 31u << 5;
info->mb = 31u << 0;
} else if (info->bpp == 32) {
info->mr = 0xffu << 16;
info->mg = 0xffu << 8;
info->mb = 0xffu << 0;
info->ma = 0xffu << 24;
info->all_a = 0; // if all_a is 0 at end, then we loaded alpha channel but it was all 0
} else {
// otherwise, use defaults, which is all-0
info->mr = info->mg = info->mb = info->ma = 0;
}
return 1;
}
return 0; // error
}
static void *stbi__bmp_parse_header(stbi__context *s, stbi__bmp_data *info)
{
int hsz;
@ -5347,6 +5373,8 @@ static void *stbi__bmp_parse_header(stbi__context *s, stbi__bmp_data *info)
if (hsz != 12) {
int compress = stbi__get32le(s);
if (compress == 1 || compress == 2) return stbi__errpuc("BMP RLE", "BMP type not supported: RLE");
if (compress >= 4) return stbi__errpuc("BMP JPEG/PNG", "BMP type not supported: unsupported compression"); // this includes PNG/JPEG modes
if (compress == 3 && info->bpp != 16 && info->bpp != 32) return stbi__errpuc("bad BMP", "bad BMP"); // bitfields requires 16 or 32 bits/pixel
stbi__get32le(s); // discard sizeof
stbi__get32le(s); // discard hres
stbi__get32le(s); // discard vres
@ -5361,17 +5389,7 @@ static void *stbi__bmp_parse_header(stbi__context *s, stbi__bmp_data *info)
}
if (info->bpp == 16 || info->bpp == 32) {
if (compress == 0) {
if (info->bpp == 32) {
info->mr = 0xffu << 16;
info->mg = 0xffu << 8;
info->mb = 0xffu << 0;
info->ma = 0xffu << 24;
info->all_a = 0; // if all_a is 0 at end, then we loaded alpha channel but it was all 0
} else {
info->mr = 31u << 10;
info->mg = 31u << 5;
info->mb = 31u << 0;
}
stbi__bmp_set_mask_defaults(info, compress);
} else if (compress == 3) {
info->mr = stbi__get32le(s);
info->mg = stbi__get32le(s);
@ -5386,6 +5404,7 @@ static void *stbi__bmp_parse_header(stbi__context *s, stbi__bmp_data *info)
return stbi__errpuc("bad BMP", "bad BMP");
}
} else {
// V4/V5 header
int i;
if (hsz != 108 && hsz != 124)
return stbi__errpuc("bad BMP", "bad BMP");
@ -5393,6 +5412,8 @@ static void *stbi__bmp_parse_header(stbi__context *s, stbi__bmp_data *info)
info->mg = stbi__get32le(s);
info->mb = stbi__get32le(s);
info->ma = stbi__get32le(s);
if (compress != 3) // override mr/mg/mb unless in BI_BITFIELDS mode, as per docs
stbi__bmp_set_mask_defaults(info, compress);
stbi__get32le(s); // discard color space
for (i=0; i < 12; ++i)
stbi__get32le(s); // discard color space parameters