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LibGfx/GIF: Only parse global color table if header flag is set

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This fixes an issue where GIF images without a global color table would
have the first segment incorrectly interpreted as color table data.

Makes many more screenshots appear on https://virtuallyfun.com/ :^)
This commit is contained in:
Andreas Kling 2024-01-04 21:19:53 +01:00
parent a1d669fe63
commit 182a2b0c3a
2 changed files with 75 additions and 10 deletions
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26
Userland/Libraries/LibGfx/ImageFormats/GIFLoader.cpp
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@ -240,20 +240,26 @@ static ErrorOr<void> load_header_and_logical_screen(GIFLoadingContext& context)
context.logical_screen.width = TRY(context.stream.read_value<LittleEndian<u16>>());
context.logical_screen.height = TRY(context.stream.read_value<LittleEndian<u16>>());
auto gcm_info = TRY(context.stream.read_value<u8>());
auto packed_fields = TRY(context.stream.read_value<u8>());
context.background_color_index = TRY(context.stream.read_value<u8>());
[[maybe_unused]] auto pixel_aspect_ratio = TRY(context.stream.read_value<u8>());
u8 bits_per_pixel = (gcm_info & 7) + 1;
int color_map_entry_count = 1;
for (int i = 0; i < bits_per_pixel; ++i)
color_map_entry_count *= 2;
// Global Color Table; if the flag is set, the Global Color Table will
// immediately follow the Logical Screen Descriptor.
bool global_color_table_flag = packed_fields & 0x80;
for (int i = 0; i < color_map_entry_count; ++i) {
u8 r = TRY(context.stream.read_value<u8>());
u8 g = TRY(context.stream.read_value<u8>());
u8 b = TRY(context.stream.read_value<u8>());
context.logical_screen.color_map[i] = { r, g, b };
if (global_color_table_flag) {
u8 bits_per_pixel = (packed_fields & 7) + 1;
int color_map_entry_count = 1;
for (int i = 0; i < bits_per_pixel; ++i)
color_map_entry_count *= 2;
for (int i = 0; i < color_map_entry_count; ++i) {
u8 r = TRY(context.stream.read_value<u8>());
u8 g = TRY(context.stream.read_value<u8>());
u8 b = TRY(context.stream.read_value<u8>());
context.logical_screen.color_map[i] = { r, g, b };
}
}
return {};