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loadbmp: Attempt to handle small palettes better.

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Only adjust the biClrUsed field if it is set to zero in the bitmap, and make
some effort to make sure we don't overflow a buffer in any case.

This was triggering an issue with the sailboat bmp used for testpalette.c in
SDL 1.2, which is an 8-bit paletted image with 66 palette entries instead of
256. See discussion at https://github.com/libsdl-org/sdl12-compat/issues/63

This change might be a problem, but there's no indication this code, which
originally landed in SDL_image 17 years ago with a large rewrite, is actually
fixing a specific issue. I'm also not sure we should actually make an effort
to accept a bmp that has a biClrUsed field that is both non-zero and _also_
incorrect.
This commit is contained in:
Ryan C. Gordon 2021-05-27 10:40:41 -04:00
parent db146e66c6
commit fed8465085
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GPG Key ID: FA148B892AB48044
1 changed files with 14 additions and 8 deletions
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22
src/video/SDL_bmp.c
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@ -407,14 +407,20 @@ SDL_LoadBMP_RW(SDL_RWops * src, int freesrc)
goto done;
}
/*
| guich: always use 1<<bpp b/c some bitmaps can bring wrong information
| for colorsUsed
*/
/* if (biClrUsed == 0) { */
biClrUsed = 1 << biBitCount;
/* } */
if (biSize == 12) {
if (biClrUsed == 0) {
biClrUsed = 1 << biBitCount;
}
if (biClrUsed > palette->ncolors) {
biClrUsed = 1 << biBitCount; /* try forcing it? */
if (biClrUsed > palette->ncolors) {
SDL_SetError("Unsupported or incorrect biClrUsed field");
was_error = SDL_TRUE;
goto done;
}
}
if (biSize == 12) {
for (i = 0; i < (int) biClrUsed; ++i) {
SDL_RWread(src, &palette->colors[i].b, 1, 1);
SDL_RWread(src, &palette->colors[i].g, 1, 1);