d1b5eec154
This basically adds the line
u8 token = TRY(
tree_decode(decoder, COEFFICIENT_TREE,
header.coefficient_probabilities[plane][band][tricky],
last_decoded_value == DCT_0 ? 2 : 0));
and calls it once for the 16 coefficients of a discrete cosine transform
that covers a 4x4 pixel subblock.
And then it does this 24 or 25 times per macroblock, for the 4x4 Y
subblocks and the 2x2 each U and V subblocks (plus an optional Y2 block
for some macroblocks).
It then adds a whole bunch of machinery to be able to compute `plane`,
`band`, and in particular `tricky` (which depends on if the
corresponding left or above subblock has non-zero coefficients).
(It also does dequantization, and does an inverse Walsh-Hadamard
transform when needed, to end up with complete DCT coefficients
in all cases.)
32 lines
762 B
C++
32 lines
762 B
C++
/*
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* Copyright (c) 2023, Nico Weber <thakis@chromium.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Span.h>
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#include <AK/Types.h>
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#include <LibGfx/Bitmap.h>
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namespace Gfx {
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struct VP8Header {
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u8 version;
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bool show_frame;
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u32 size_of_first_partition;
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u32 width;
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u8 horizontal_scale;
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u32 height;
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u8 vertical_scale;
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ReadonlyBytes first_partition;
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ReadonlyBytes second_partition;
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};
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// Parses the header data in a VP8 chunk. Pass the payload of a `VP8 ` chunk, after the tag and after the tag's data size.
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ErrorOr<VP8Header> decode_webp_chunk_VP8_header(ReadonlyBytes vp8_data);
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ErrorOr<NonnullRefPtr<Bitmap>> decode_webp_chunk_VP8_contents(VP8Header const&, bool include_alpha_channel);
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}
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