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bmp: Correctly load RLE-encoded bitmaps with irregular widths.

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(Such as a 4-bpp image--two pixels per byte--with an odd number of pixels.)

Fixes #16210.

(cherry picked from commit c71abd0860)
This commit is contained in:
Ryan C. Gordon
2026-08-28 21:20:32 -04:00
parent 8b2ecd481b
commit 58ff755ea5
1 changed files with 17 additions and 7 deletions
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24
src/video/SDL_bmp.c
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@@ -96,10 +96,11 @@ static bool readRlePixels(SDL_Surface *surface, SDL_IOStream *src, int isRle8)
if (!SDL_ReadU8(src, &pixelvalue)) {
return false;
}
ch /= pixels_per_byte;
int ich = (int) ch;
do {
COPY_PIXEL(pixelvalue);
} while (--ch);
ich -= pixels_per_byte;
} while (ich > 0);
} else {
/*
| A leading zero is an escape; it may signal the end of the bitmap,
@@ -121,22 +122,31 @@ static bool readRlePixels(SDL_Surface *surface, SDL_IOStream *src, int isRle8)
return false;
}
ofs += ch / pixels_per_byte;
if (ch & pixels_per_byte) {
ofs++;
}
if (!SDL_ReadU8(src, &ch)) {
return false;
}
bits -= ((ch / pixels_per_byte) * pitch);
bits -= (ch * pitch);
break;
default: // no compression
ch /= pixels_per_byte;
needsPad = (ch & 1);
// !!! FIXME: this needsPad calculation can probably be simpler than this.
if (pixels_per_byte == 1) {
needsPad = (ch & 1) != 0;
} else {
needsPad = (((ch + (pixels_per_byte-1)) / pixels_per_byte) & (pixels_per_byte-1)) != 0;
}
int ich = (int) ch;
do {
Uint8 pixelvalue;
if (!SDL_ReadU8(src, &pixelvalue)) {
return false;
}
COPY_PIXEL(pixelvalue);
} while (--ch);
ich -= pixels_per_byte;
} while (ich > 0);
// pad at even boundary
if (needsPad && !SDL_ReadU8(src, &ch)) {