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LibGfx/WebPWriter: Move VP8L compression to WebPWriterLossless.{h,cpp}
* Matches how the loader is organized * `compress_VP8L_image_data()` will grow longer when we add actual compression * Maybe someone wants to write a lossy compressor one day No behavior change.
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150 changes: 150 additions & 0 deletions
150
Userland/Libraries/LibGfx/ImageFormats/WebPWriterLossless.cpp
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| /* | ||
| * Copyright (c) 2024, Nico Weber <thakis@chromium.org> | ||
| * | ||
| * SPDX-License-Identifier: BSD-2-Clause | ||
| */ | ||
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| // Lossless format: https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification | ||
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| #include <AK/BitStream.h> | ||
| #include <AK/Debug.h> | ||
| #include <AK/Endian.h> | ||
| #include <AK/MemoryStream.h> | ||
| #include <LibCompress/DeflateTables.h> | ||
| #include <LibGfx/Bitmap.h> | ||
| #include <LibGfx/ImageFormats/WebPWriterLossless.h> | ||
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| namespace Gfx { | ||
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| static bool are_all_pixels_opaque(Bitmap const& bitmap) | ||
| { | ||
| for (ARGB32 pixel : bitmap) { | ||
| if ((pixel >> 24) != 0xff) | ||
| return false; | ||
| } | ||
| return true; | ||
| } | ||
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| static ErrorOr<void> write_VP8L_image_data(Stream& stream, Bitmap const& bitmap) | ||
| { | ||
| LittleEndianOutputBitStream bit_stream { MaybeOwned<Stream>(stream) }; | ||
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| // optional-transform = (%b1 transform optional-transform) / %b0 | ||
| TRY(bit_stream.write_bits(0u, 1u)); // No transform for now. | ||
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| // https://developers.google.com/speed/webp/docs/webp_lossless_bitstream_specification#5_image_data | ||
| // spatially-coded-image = color-cache-info meta-prefix data | ||
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| // color-cache-info = %b0 | ||
| // color-cache-info =/ (%b1 4BIT) ; 1 followed by color cache size | ||
| TRY(bit_stream.write_bits(0u, 1u)); // No color cache for now. | ||
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| // meta-prefix = %b0 / (%b1 entropy-image) | ||
| TRY(bit_stream.write_bits(0u, 1u)); // No meta prefix for now. | ||
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| // data = prefix-codes lz77-coded-image | ||
| // prefix-codes = prefix-code-group *prefix-codes | ||
| // prefix-code-group = | ||
| // 5prefix-code ; See "Interpretation of Meta Prefix Codes" to | ||
| // ; understand what each of these five prefix | ||
| // ; codes are for. | ||
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| // We're writing a single prefix-code-group. | ||
| // "These codes are (in bitstream order): | ||
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| // Prefix code #1: Used for green channel, backward-reference length, and color cache. | ||
| // Prefix code #2, #3, and #4: Used for red, blue, and alpha channels, respectively. | ||
| // Prefix code #5: Used for backward-reference distance." | ||
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| // We use neither back-references not color cache entries yet. | ||
| // We write prefix trees for 256 literals all of length 8, which means each byte is encoded as itself. | ||
| // That doesn't give any compression, but is a valid bit stream. | ||
| // We can make this smarter later on. | ||
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| size_t const color_cache_size = 0; | ||
| constexpr Array alphabet_sizes = to_array<size_t>({ 256 + 24 + static_cast<size_t>(color_cache_size), 256, 256, 256, 40 }); // XXX Shared? | ||
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| // If you add support for color cache: At the moment, CanonicalCodes does not support writing more than 288 symbols. | ||
| if (alphabet_sizes[0] > 288) | ||
| return Error::from_string_literal("Invalid alphabet size"); | ||
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| bool all_pixels_are_opaque = are_all_pixels_opaque(bitmap); | ||
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| int number_of_full_channels = all_pixels_are_opaque ? 3 : 4; | ||
| for (int i = 0; i < number_of_full_channels; ++i) { | ||
| TRY(bit_stream.write_bits(0u, 1u)); // Normal code length code. | ||
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| // Write code length codes. | ||
| constexpr int kCodeLengthCodes = 19; | ||
| Array<int, kCodeLengthCodes> kCodeLengthCodeOrder = { 17, 18, 0, 1, 2, 3, 4, 5, 16, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 }; | ||
| int num_code_lengths = max(4u, find_index(kCodeLengthCodeOrder.begin(), kCodeLengthCodeOrder.end(), 8) + 1); | ||
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| // "int num_code_lengths = 4 + ReadBits(4);" | ||
| TRY(bit_stream.write_bits(num_code_lengths - 4u, 4u)); | ||
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| for (int i = 0; i < num_code_lengths - 1; ++i) | ||
| TRY(bit_stream.write_bits(0u, 3u)); | ||
| TRY(bit_stream.write_bits(1u, 3u)); | ||
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| // Write code lengths. | ||
| if (alphabet_sizes[i] == 256) { | ||
| TRY(bit_stream.write_bits(0u, 1u)); // max_symbol is alphabet_size | ||
| } else { | ||
| TRY(bit_stream.write_bits(1u, 1u)); // max_symbol is explicitly coded | ||
| // "int length_nbits = 2 + 2 * ReadBits(3); | ||
| // int max_symbol = 2 + ReadBits(length_nbits);" | ||
| TRY(bit_stream.write_bits(3u, 3u)); // length_nbits = 2 + 2 * 3 | ||
| TRY(bit_stream.write_bits(254u, 8u)); // max_symbol = 2 + 254 | ||
| } | ||
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| // The code length codes only contain a single entry for '8'. WebP streams with a single element store 0 bits per element. | ||
| // (This is different from deflate, which needs 1 bit per element.) | ||
| } | ||
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| if (all_pixels_are_opaque) { | ||
| // Use a simple 1-element code. | ||
| TRY(bit_stream.write_bits(1u, 1u)); // Simple code length code. | ||
| TRY(bit_stream.write_bits(0u, 1u)); // num_symbols - 1 | ||
| TRY(bit_stream.write_bits(1u, 1u)); // is_first_8bits | ||
| TRY(bit_stream.write_bits(255u, 8u)); // symbol0 | ||
| } | ||
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| // For code #5, use a simple empty code, since we don't use this yet. | ||
| TRY(bit_stream.write_bits(1u, 1u)); // Simple code length code. | ||
| TRY(bit_stream.write_bits(0u, 1u)); // num_symbols - 1 | ||
| TRY(bit_stream.write_bits(0u, 1u)); // is_first_8bits | ||
| TRY(bit_stream.write_bits(0u, 1u)); // symbol0 | ||
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| // Image data. | ||
| for (ARGB32 pixel : bitmap) { | ||
| u8 a = pixel >> 24; | ||
| u8 r = pixel >> 16; | ||
| u8 g = pixel >> 8; | ||
| u8 b = pixel; | ||
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| // We wrote a huffman table that gives every symbol 8 bits. That means we can write the image data | ||
| // out uncompressed –- but we do need to reverse the bit order of the bytes. | ||
| TRY(bit_stream.write_bits(Compress::reverse8_lookup_table[g], 8u)); | ||
| TRY(bit_stream.write_bits(Compress::reverse8_lookup_table[r], 8u)); | ||
| TRY(bit_stream.write_bits(Compress::reverse8_lookup_table[b], 8u)); | ||
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| // If all pixels are opaque, we wrote a one-element huffman table for alpha, which needs 0 bits per element. | ||
| if (!all_pixels_are_opaque) | ||
| TRY(bit_stream.write_bits(Compress::reverse8_lookup_table[a], 8u)); | ||
| } | ||
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| // FIXME: Make ~LittleEndianOutputBitStream do this, or make it VERIFY() that it has happened at least. | ||
| TRY(bit_stream.align_to_byte_boundary()); | ||
| TRY(bit_stream.flush_buffer_to_stream()); | ||
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| return {}; | ||
| } | ||
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| ErrorOr<ByteBuffer> compress_VP8L_image_data(Bitmap const& bitmap) | ||
| { | ||
| AllocatingMemoryStream vp8l_data_stream; | ||
| TRY(write_VP8L_image_data(vp8l_data_stream, bitmap)); | ||
| return vp8l_data_stream.read_until_eof(); | ||
| } | ||
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| } |
16 changes: 16 additions & 0 deletions
16
Userland/Libraries/LibGfx/ImageFormats/WebPWriterLossless.h
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,16 @@ | ||
| /* | ||
| * Copyright (c) 2024, Nico Weber <thakis@chromium.org> | ||
| * | ||
| * SPDX-License-Identifier: BSD-2-Clause | ||
| */ | ||
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| #pragma once | ||
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| #include <AK/Error.h> | ||
| #include <LibGfx/Forward.h> | ||
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| namespace Gfx { | ||
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| ErrorOr<ByteBuffer> compress_VP8L_image_data(Bitmap const&); | ||
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| } |