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LibGfx: Parse WebP VP8L chunk header

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For now, just dbgln_if() all data. Eventually we'll want to use at
least width and height.
This commit is contained in:
Nico Weber 2023-02-24 23:15:22 -05:00 committed by Linus Groh
parent d5875b5962
commit 7c1455c357
Notes: sideshowbarker 2024-07-17 00:53:02 +09:00 
Author: https://github.com/nico
Commit: https://github.com/SerenityOS/serenity/commit/7c1455c357
Pull-request: https://github.com/SerenityOS/serenity/pull/17603
Reviewed-by: https://github.com/linusg
1 changed files with 25 additions and 3 deletions
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28
Userland/Libraries/LibGfx/WebPLoader.cpp
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@ -204,11 +204,33 @@ static ErrorOr<void> decode_webp_simple_lossy(WebPLoadingContext& context, Chunk
}
// https://developers.google.com/speed/webp/docs/riff_container#simple_file_format_lossless
// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#7_overall_structure_of_the_format
static ErrorOr<void> decode_webp_simple_lossless(WebPLoadingContext& context, Chunk const& vp8l_chunk)
{
// FIXME
(void)context;
(void)vp8l_chunk;
VERIFY(vp8l_chunk.type == FourCC("VP8L"));
// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#3_riff_header
if (vp8l_chunk.data.size() < 5)
return context.error("WebPImageDecoderPlugin: VP8L chunk too small");
u8 const* data = vp8l_chunk.data.data();
u8 signature = data[0];
if (signature != 0x2f)
return context.error("WebPImageDecoderPlugin: VP8L chunk invalid signature");
// 14 bits width-1, 14 bits height-1, 1 bit alpha hint, 3 bit version_number.
u16 width = (data[1] | ((data[2] & 0x3f) << 8)) + 1;
u16 height = ((data[2] >> 6) | (data[3] << 2) | ((data[4] & 0xf) << 12)) + 1;
bool is_alpha_used = (data[4] & 0x10) != 0;
u8 version_number = (data[4] & 0xe0) >> 5;
dbgln_if(WEBP_DEBUG, "width {}, height {}, is_alpha_used {}, version_number {}",
width, height, is_alpha_used, version_number);
// "The version_number is a 3 bit code that must be set to 0. Any other value should be treated as an error. [AMENDED]"
if (version_number != 0)
return context.error("WebPImageDecoderPlugin: VP8L chunk invalid version_number");
return {};
}