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LibGfx: Teach webp image reading function to read entropy coded images

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Nico Weber 2023-04-04 09:45:09 -04:00 • committed by Linus Groh
parent 4bd7090bc5
commit 48f88b3cdd
Notes: sideshowbarker 2024-07-17 05:18:58 +09:00
1 changed files with 17 additions and 9 deletions
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26
Userland/Libraries/LibGfx/ImageFormats/WebPLoader.cpp
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@ -443,11 +443,17 @@ static ErrorOr<PrefixCodeGroup> decode_webp_chunk_VP8L_prefix_code_group(WebPLoa
return group;
}
static ErrorOr<NonnullRefPtr<Bitmap>> decode_webp_chunk_VP8L_image(WebPLoadingContext& context, VP8LHeader const& vp8l_header, LittleEndianInputBitStream& bit_stream)
enum class ImageKind {
SpatiallyCoded,
EntropyCoded,
};
static ErrorOr<NonnullRefPtr<Bitmap>> decode_webp_chunk_VP8L_image(WebPLoadingContext& context, ImageKind image_kind, VP8LHeader const& vp8l_header, LittleEndianInputBitStream& bit_stream)
{
// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#623_decoding_entropy-coded_image_data
// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#523_color_cache_coding
// spatially-coded-image = color-cache-info meta-prefix data
// entropy-coded-image = color-cache-info data
// color-cache-info = %b0
// color-cache-info =/ (%b1 4BIT) ; 1 followed by color cache size
@ -469,13 +475,15 @@ static ErrorOr<NonnullRefPtr<Bitmap>> decode_webp_chunk_VP8L_image(WebPLoadingCo
TRY(color_cache.try_resize(color_cache_size));
}
// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#622_decoding_of_meta_prefix_codes
// "Meta prefix codes may be used only when the image is being used in the role of an ARGB image."
// meta-prefix = %b0 / (%b1 entropy-image)
bool has_meta_prefix = TRY(bit_stream.read_bits(1));
dbgln_if(WEBP_DEBUG, "has_meta_prefix {}", has_meta_prefix);
if (has_meta_prefix)
return context.error("WebPImageDecoderPlugin: VP8L meta_prefix not yet implemented");
if (image_kind == ImageKind::SpatiallyCoded) {
// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#622_decoding_of_meta_prefix_codes
// "Meta prefix codes may be used only when the image is being used in the role of an ARGB image."
// meta-prefix = %b0 / (%b1 entropy-image)
bool has_meta_prefix = TRY(bit_stream.read_bits(1));
dbgln_if(WEBP_DEBUG, "has_meta_prefix {}", has_meta_prefix);
if (has_meta_prefix)
return context.error("WebPImageDecoderPlugin: VP8L meta_prefix not yet implemented");
}
// https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#52_encoding_of_image_data
// "The encoded image data consists of several parts:
@ -673,7 +681,7 @@ static ErrorOr<void> decode_webp_chunk_VP8L(WebPLoadingContext& context, Chunk c
}
}
context.bitmap = TRY(decode_webp_chunk_VP8L_image(context, vp8l_header, bit_stream));
context.bitmap = TRY(decode_webp_chunk_VP8L_image(context, ImageKind::SpatiallyCoded, vp8l_header, bit_stream));
return {};
}