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banan-os/userspace/libraries/LibImage/PNG.cpp

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#include <BAN/Debug.h>
#include <BAN/Endianness.h>
#include <LibImage/PNG.h>
#include <ctype.h>
#define DEBUG_PNG 0
// PNG https://www.w3.org/TR/png-3/
// ZLIB https://www.rfc-editor.org/rfc/rfc1950
// DEFLATE https://www.rfc-editor.org/rfc/rfc1951
namespace LibImage
{
template<BAN::integral T>
struct PODNetworkEndian
{
T raw;
constexpr operator T() const { return BAN::network_endian_to_host(raw); }
};
enum class ColourType : uint8_t
{
Greyscale = 0,
Truecolour = 2,
IndexedColour = 3,
GreyscaleAlpha = 4,
TruecolourAlpha = 6,
};
enum class CompressionMethod : uint8_t
{
Deflate = 0,
};
enum class FilterMethod : uint8_t
{
Adaptive = 0,
};
enum class FilterType : uint8_t
{
None = 0,
Sub = 1,
Up = 2,
Average = 3,
Paeth = 4,
};
enum class InterlaceMethod : uint8_t
{
NoInterlace = 0,
Adam7 = 1,
};
struct IHDR
{
PODNetworkEndian<uint32_t> width;
PODNetworkEndian<uint32_t> height;
uint8_t bit_depth;
ColourType colour_type;
CompressionMethod compression_method;
FilterMethod filter_method;
InterlaceMethod interlace_method;
} __attribute__((packed));
struct ZLibStream
{
uint8_t cm : 4;
uint8_t cinfo : 4;
uint8_t fcheck : 5;
uint8_t fdict : 1;
uint8_t flevel : 2;
};
struct PNGChunk
{
BAN::StringView name;
BAN::ConstByteSpan data;
};
class BitBuffer
{
public:
BitBuffer(BAN::Vector<BAN::ConstByteSpan> data)
: m_data(data)
{}
BAN::ErrorOr<uint16_t> peek_bits(uint8_t count)
{
ASSERT(count <= 16);
while (m_bit_buffer_len < count)
{
if (m_data.empty())
return BAN::Error::from_errno(ENODATA);
m_bit_buffer |= m_data[0][0] << m_bit_buffer_len;
m_bit_buffer_len += 8;
if (m_data[0].size() > 1)
m_data[0] = m_data[0].slice(1);
else
m_data.remove(0);
}
return m_bit_buffer & ((1 << count) - 1);
}
void remove_bits(uint8_t count)
{
ASSERT(count <= 16);
ASSERT(m_bit_buffer_len >= count);
m_bit_buffer_len -= count;
m_bit_buffer >>= count;
}
BAN::ErrorOr<uint16_t> get_bits(uint8_t count)
{
uint16_t result = TRY(peek_bits(count));
remove_bits(count);
return result;
}
void skip_to_byte_boundary()
{
m_bit_buffer >>= m_bit_buffer_len % 8;
m_bit_buffer_len -= m_bit_buffer_len % 8;
}
private:
BAN::Vector<BAN::ConstByteSpan> m_data;
uint32_t m_bit_buffer { 0 };
uint8_t m_bit_buffer_len { 0 };
};
constexpr uint16_t reverse_bits(uint16_t value, uint8_t count)
{
uint16_t reverse = 0;
for (uint8_t bit = 0; bit < count; bit++)
reverse |= ((value >> bit) & 1) << (count - bit - 1);
return reverse;
}
class HuffmanTree
{
public:
static constexpr uint8_t MAX_BITS = 15;
struct Leaf
{
uint16_t code;
uint8_t len;
};
public:
HuffmanTree() = default;
HuffmanTree(BAN::Vector<Leaf>&& leaves, uint8_t min_len, uint8_t max_len, uint8_t instant_max_bit)
: m_leaves(BAN::move(leaves))
, m_min_bits(min_len), m_max_bits(max_len)
, m_instant_max_bit(instant_max_bit)
{}
uint8_t min_bits() const { return m_min_bits; }
uint8_t max_bits() const { return m_max_bits; }
uint8_t instant_max_bit() const { return m_instant_max_bit; }
Leaf get_leaf(size_t index) const { return m_leaves[index]; }
bool empty() const { return m_leaves.empty(); }
static BAN::ErrorOr<HuffmanTree> create(const BAN::Vector<uint8_t>& bit_lengths)
{
uint16_t bl_count[MAX_BITS] {};
for (uint8_t bl : bit_lengths)
bl_count[bl]++;
bl_count[0] = 0;
uint8_t min_bits = MAX_BITS;
uint8_t max_bits = 0;
for (uint8_t bits = 0; bits <= MAX_BITS; bits++)
{
if (bit_lengths[bits] == 0)
continue;
min_bits = BAN::Math::min(min_bits, bits);
max_bits = BAN::Math::max(max_bits, bits);
}
uint8_t instant_max_bit = BAN::Math::min<uint8_t>(10, max_bits);
uint16_t instant_mask = (1 << instant_max_bit) - 1;
uint16_t code = 0;
uint16_t next_code[MAX_BITS + 1] {};
for (uint8_t bits = 1; bits <= max_bits; bits++)
{
code = (code + bl_count[bits - 1]) << 1;
next_code[bits] = code;
}
BAN::Vector<Leaf> leaves;
TRY(leaves.resize(1 << max_bits));
for (uint16_t n = 0; n < bit_lengths.size(); n++)
{
uint8_t bits = bit_lengths[n];
if (bits == 0)
continue;
uint16_t canonical = next_code[bits];
next_code[bits]++;
uint16_t reversed = reverse_bits(canonical, bits);
leaves[reversed] = Leaf { n, bits };
if (bits <= instant_max_bit)
{
uint16_t step = 1 << bits;
for (uint16_t spread = reversed + step; spread <= instant_mask; spread += step)
leaves[spread] = Leaf { n, bits };
}
}
return HuffmanTree(BAN::move(leaves), min_bits, max_bits, instant_max_bit);
}
static BAN::ErrorOr<HuffmanTree> fixed_tree()
{
BAN::Vector<uint8_t> bit_lengths;
TRY(bit_lengths.resize(288));
size_t i = 0;
for (; i <= 143; i++) bit_lengths[i] = 8;
for (; i <= 255; i++) bit_lengths[i] = 9;
for (; i <= 279; i++) bit_lengths[i] = 7;
for (; i <= 287; i++) bit_lengths[i] = 8;
return TRY(HuffmanTree::create(bit_lengths));
}
private:
BAN::Vector<Leaf> m_leaves;
uint8_t m_min_bits { 0 };
uint8_t m_max_bits { 0 };
uint8_t m_instant_max_bit { 0 };
};
class DeflateDecoder
{
public:
DeflateDecoder(BAN::Vector<BAN::ConstByteSpan> data)
: m_buffer(BitBuffer(BAN::move(data)))
{}
BAN::ErrorOr<BAN::ByteSpan> decode_stream()
{
while (!TRY(decode_block()))
continue;
m_buffer.skip_to_byte_boundary();
uint32_t checksum = 0;
for (int i = 0; i < 4; i++)
checksum = (checksum << 8) | TRY(m_buffer.get_bits(8));
if (decoded_adler32() != checksum)
{
dwarnln_if(DEBUG_PNG, "decode checksum does not match");
return BAN::Error::from_errno(EINVAL);
}
return BAN::ByteSpan(m_decoded.span());
}
private:
uint32_t decoded_adler32() const
{
uint32_t a = 1;
uint32_t b = 0;
for (uint8_t byte : m_decoded)
{
a = (a + byte) % 65521;
b = (b + a) % 65521;
}
return (b << 16) | a;
}
BAN::ErrorOr<bool> decode_block()
{
bool bfinal = TRY(m_buffer.get_bits(1));
uint8_t btype = TRY(m_buffer.get_bits(2));
switch (btype)
{
case 0: TRY(decode_type0()); break;
case 1: TRY(decode_type1()); break;
case 2: TRY(decode_type2()); break;
default:
dwarnln_if(DEBUG_PNG, "Deflate block has invalid method {}", btype);
return BAN::Error::from_errno(EINVAL);
}
return bfinal;
}
BAN::ErrorOr<void> decode_type0()
{
m_buffer.skip_to_byte_boundary();
uint16_t len = TRY(m_buffer.get_bits(16));
uint16_t nlen = TRY(m_buffer.get_bits(16));
if (len != 0xFFFF - nlen)
{
dwarnln_if(DEBUG_PNG, "Deflate block uncompressed data length is invalid");
return BAN::Error::from_errno(EINVAL);
}
TRY(m_decoded.reserve(m_decoded.size() + len));
for (uint16_t i = 0; i < len; i++)
MUST(m_decoded.push_back(TRY(m_buffer.get_bits(8))));
return {};
}
BAN::ErrorOr<void> decode_type1()
{
TRY(inflate_block(TRY(HuffmanTree::fixed_tree()), HuffmanTree()));
return {};
}
BAN::ErrorOr<void> decode_type2()
{
static constexpr uint8_t code_length_order[] {
16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
};
const uint16_t hlit = TRY(m_buffer.get_bits(5)) + 257;
const uint8_t hdist = TRY(m_buffer.get_bits(5)) + 1;
const uint8_t hclen = TRY(m_buffer.get_bits(4)) + 4;
HuffmanTree code_length_tree;
{
BAN::Vector<uint8_t> code_lengths;
TRY(code_lengths.resize(19, 0));
for (uint8_t i = 0; i < hclen; i++)
code_lengths[code_length_order[i]] = TRY(m_buffer.get_bits(3));
code_length_tree = TRY(HuffmanTree::create(code_lengths));
}
uint16_t last_symbol = 0;
BAN::Vector<uint8_t> bit_lengths;
TRY(bit_lengths.reserve(288 + 32));
while (bit_lengths.size() < hlit + hdist)
{
uint16_t symbol = TRY(read_symbol(code_length_tree));
uint8_t count = 0;
if (symbol <= 15)
{
count = 1;
}
else if (symbol == 16)
{
symbol = last_symbol;
count = TRY(m_buffer.get_bits(2)) + 3;
}
else if (symbol == 17)
{
symbol = 0;
count = TRY(m_buffer.get_bits(3)) + 3;
}
else if (symbol == 18)
{
symbol = 0;
count = TRY(m_buffer.get_bits(7)) + 11;
}
for (uint8_t i = 0; i < count; i++)
TRY(bit_lengths.push_back(symbol));
last_symbol = symbol;
}
TRY(bit_lengths.resize(hlit + 32, 0));
BAN::Vector<uint8_t> distance_lengths;
TRY(distance_lengths.resize(32));
for (uint8_t i = 0; i < 32; i++)
distance_lengths[i] = bit_lengths[hlit + i];
TRY(bit_lengths.resize(hlit));
TRY(bit_lengths.resize(288, 0));
TRY(inflate_block(TRY(HuffmanTree::create(bit_lengths)), TRY(HuffmanTree::create(distance_lengths))));
return {};
}
BAN::ErrorOr<void> inflate_block(const HuffmanTree& length_tree, const HuffmanTree& distance_tree)
{
static constexpr uint16_t length_base[] {
3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258
};
static constexpr uint8_t extra_length_bits[] {
0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0
};
static constexpr uint16_t distance_base[] {
1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 8193, 12289, 16385, 24577
};
static constexpr uint8_t extra_distance_bits[] {
0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13
};
uint16_t symbol;
while ((symbol = TRY(read_symbol(length_tree))) != 256)
{
if (symbol < 256)
{
TRY(m_decoded.push_back(symbol));
continue;
}
ASSERT(symbol <= 285);
symbol -= 257;
const uint16_t length = length_base[symbol] + TRY(m_buffer.get_bits(extra_length_bits[symbol]));
uint16_t distance_code;
if (distance_tree.empty())
distance_code = reverse_bits(TRY(m_buffer.get_bits(5)), 5);
else
distance_code = TRY(read_symbol(distance_tree));
ASSERT(distance_code <= 30);
const size_t distance = distance_base[distance_code] + TRY(m_buffer.get_bits(extra_distance_bits[distance_code]));
size_t offset = m_decoded.size() - distance;
for (size_t i = 0; i < length; i++)
TRY(m_decoded.push_back(m_decoded[offset + i]));
}
return {};
}
BAN::ErrorOr<uint16_t> read_symbol(const HuffmanTree& tree)
{
uint16_t compare = TRY(m_buffer.peek_bits(tree.max_bits()));
for (uint8_t bits = tree.instant_max_bit(); bits <= tree.max_bits(); bits++)
{
uint16_t mask = (1 << bits) - 1;
auto leaf = tree.get_leaf(compare & mask);
if (leaf.len <= bits)
{
m_buffer.remove_bits(leaf.len);
return leaf.code;
}
}
return BAN::Error::from_errno(EINVAL);
}
private:
BAN::Vector<uint8_t> m_decoded;
BitBuffer m_buffer;
};
BAN::ErrorOr<PNGChunk> read_and_take_chunk(BAN::ConstByteSpan& image_data)
{
if (image_data.size() < 12)
{
dwarnln_if(DEBUG_PNG, "PNG stream does not contain any more chunks");
return BAN::Error::from_errno(EINVAL);
}
uint32_t length = image_data.as<const BAN::NetworkEndian<uint32_t>>();
image_data = image_data.slice(4);
if (image_data.size() < length + 8)
{
dwarnln_if(DEBUG_PNG, "PNG stream does not contain any more chunks");
return BAN::Error::from_errno(EINVAL);
}
PNGChunk result;
result.name = BAN::StringView(image_data.as_span<const char>().data(), 4);
image_data = image_data.slice(4);
result.data = image_data.slice(0, length);
image_data = image_data.slice(length);
// FIXME: validate CRC
image_data = image_data.slice(4);
return result;
}
static bool validate_ihdr_colour_type_and_bit_depth(const IHDR& ihdr)
{
if (!BAN::Math::is_power_of_two(ihdr.bit_depth))
return false;
switch (ihdr.colour_type)
{
case ColourType::Greyscale:
if (ihdr.bit_depth < 1 || ihdr.bit_depth > 16)
return false;
return true;
case ColourType::Truecolour:
if (ihdr.bit_depth < 8 || ihdr.bit_depth > 16)
return false;
return true;
case ColourType::IndexedColour:
if (ihdr.bit_depth < 1 || ihdr.bit_depth > 8)
return false;
return true;
case ColourType::GreyscaleAlpha:
if (ihdr.bit_depth < 8 || ihdr.bit_depth > 16)
return false;
return true;
case ColourType::TruecolourAlpha:
if (ihdr.bit_depth < 8 || ihdr.bit_depth > 16)
return false;
return true;
default:
return false;
}
}
bool probe_png(BAN::ConstByteSpan image_data)
{
if (image_data.size() < 8)
return false;
uint64_t u64_signature = image_data.as<const uint64_t>();
return u64_signature == 0x0A1A0A0D474E5089;
}
BAN::ErrorOr<BAN::UniqPtr<Image>> load_png(BAN::ConstByteSpan image_data)
{
if (!probe_png(image_data))
{
dwarnln_if(DEBUG_PNG, "Invalid PNG data");
return BAN::Error::from_errno(EINVAL);
}
image_data = image_data.slice(8);
auto ihdr_chunk = TRY(read_and_take_chunk(image_data));
if (ihdr_chunk.name != "IHDR")
{
dwarnln_if(DEBUG_PNG, "PNG stream does not start with IHDR chunk");
return BAN::Error::from_errno(EINVAL);
}
if (ihdr_chunk.data.size() != sizeof(IHDR))
{
dwarnln_if(DEBUG_PNG, "PNG stream has invalid IHDR chunk size: {}, expected {}", ihdr_chunk.data.size(), sizeof(IHDR));
return BAN::Error::from_errno(EINVAL);
}
const auto& ihdr = ihdr_chunk.data.as<const IHDR>();
if (ihdr.width == 0 || ihdr.height == 0 || ihdr.width > 0x7FFFFFFF || ihdr.height > 0x7FFFFFFF)
{
dwarnln_if(DEBUG_PNG, "PNG IHDR has invalid size {}x{}", (uint32_t)ihdr.width, (uint32_t)ihdr.height);
return BAN::Error::from_errno(EINVAL);
}
if (!validate_ihdr_colour_type_and_bit_depth(ihdr))
{
dwarnln_if(DEBUG_PNG, "PNG IHDR has invalid bit depth {} for colour type {}", ihdr.bit_depth, static_cast<uint8_t>(ihdr.colour_type));
return BAN::Error::from_errno(EINVAL);
}
if (ihdr.compression_method != CompressionMethod::Deflate)
{
dwarnln_if(DEBUG_PNG, "PNG IHDR has invalid compression method {}", static_cast<uint8_t>(ihdr.compression_method));
return BAN::Error::from_errno(EINVAL);
}
if (ihdr.filter_method != FilterMethod::Adaptive)
{
dwarnln_if(DEBUG_PNG, "PNG IHDR has invalid filter method {}", static_cast<uint8_t>(ihdr.filter_method));
return BAN::Error::from_errno(EINVAL);
}
if (ihdr.interlace_method != InterlaceMethod::NoInterlace && ihdr.interlace_method != InterlaceMethod::Adam7)
{
dwarnln_if(DEBUG_PNG, "PNG IHDR has invalid interlace method {}", static_cast<uint8_t>(ihdr.interlace_method));
return BAN::Error::from_errno(EINVAL);
}
if (ihdr.interlace_method == InterlaceMethod::Adam7)
{
dwarnln_if(DEBUG_PNG, "PNG with interlacing is not supported");
return BAN::Error::from_errno(ENOTSUP);
}
const uint64_t image_width = ihdr.width;
const uint64_t image_height = ihdr.height;
dprintln_if(DEBUG_PNG, "Decoding {}x{} PNG image", image_width, image_height);
dprintln_if(DEBUG_PNG, " bit depth: {}", ihdr.bit_depth);
dprintln_if(DEBUG_PNG, " colour type: {}", static_cast<uint8_t>(ihdr.colour_type));
dprintln_if(DEBUG_PNG, " compression method: {}", static_cast<uint8_t>(ihdr.compression_method));
dprintln_if(DEBUG_PNG, " filter method: {}", static_cast<uint8_t>(ihdr.filter_method));
dprintln_if(DEBUG_PNG, " interlace method: {}", static_cast<uint8_t>(ihdr.interlace_method));
BAN::Vector<Image::Color> palette;
BAN::Vector<BAN::ConstByteSpan> zlib_stream;
while (true)
{
PNGChunk chunk;
if (auto ret = read_and_take_chunk(image_data); !ret.is_error())
chunk = ret.release_value();
else
{
dwarnln_if(DEBUG_PNG, "PNG stream does not end with IEND chunk");
return BAN::Error::from_errno(EINVAL);
}
if (chunk.name == "IHDR"_sv)
{
dwarnln_if(DEBUG_PNG, "PNG stream has IDHR chunk defined multiple times");
return BAN::Error::from_errno(EINVAL);
}
else if (chunk.name == "PLTE"_sv)
{
if (chunk.data.size() == 0 || chunk.data.size() % 3)
{
dwarnln_if(DEBUG_PNG, "PNG PLTE has invalid data size {}", chunk.data.size());
return BAN::Error::from_errno(EINVAL);
}
if (!palette.empty())
{
dwarnln_if(DEBUG_PNG, "PNG PLTE defined multiple times");
return BAN::Error::from_errno(EINVAL);
}
if (ihdr.colour_type != ColourType::IndexedColour && ihdr.colour_type != ColourType::Truecolour && ihdr.colour_type != ColourType::TruecolourAlpha)
{
dwarnln_if(DEBUG_PNG, "PNG PLTE defined for colour type {} which does not use palette", static_cast<uint8_t>(ihdr.colour_type));
return BAN::Error::from_errno(EINVAL);
}
TRY(palette.resize(chunk.data.size() / 3));
for (size_t i = 0; i < palette.size(); i += 3)
{
palette[i].r = chunk.data[i + 0];
palette[i].g = chunk.data[i + 1];
palette[i].b = chunk.data[i + 2];
palette[i].a = 0xFF;
}
}
else if (chunk.name == "IDAT"_sv)
{
TRY(zlib_stream.push_back(chunk.data));
}
else if (chunk.name == "IEND"_sv)
{
break;
}
else if (chunk.name == "tEXt"_sv)
{
auto data_sv = BAN::StringView(chunk.data.as_span<const char>().data(), chunk.data.size());
if (auto idx = data_sv.find('\0'); !idx.has_value())
dwarnln_if(DEBUG_PNG, "PNG tEXt chunk does not contain null-byte");
else
{
auto keyword = data_sv.substring(0, idx.value());
auto text = data_sv.substring(idx.value() + 1);
dprintln_if(DEBUG_PNG, "'{}': '{}'", keyword, text);
}
}
else
{
bool ancillary = islower(chunk.name[0]);
if (!ancillary)
{
dwarnln_if(DEBUG_PNG, "Unsupported critical chunk '{}'", chunk.name);
return BAN::Error::from_errno(ENOTSUP);
}
dwarnln_if(DEBUG_PNG, "Skipping unsupported ancillary chunk '{}'", chunk.name);
}
}
{
if (zlib_stream.empty() || zlib_stream.front().size() < 2)
{
dwarnln_if(DEBUG_PNG, "PNG does not have zlib stream");
return BAN::Error::from_errno(EINVAL);
}
if (zlib_stream[0].as<const BAN::BigEndian<uint16_t>>() % 31)
{
dwarnln_if(DEBUG_PNG, "PNG zlib stream checksum failed");
return BAN::Error::from_errno(EINVAL);
}
auto zlib_header = zlib_stream[0].as<const ZLibStream>();
if (zlib_header.fdict)
{
dwarnln_if(DEBUG_PNG, "PNG IDAT zlib stream has fdict set");
return BAN::Error::from_errno(EINVAL);
}
if (zlib_header.cm != 8)
{
dwarnln_if(DEBUG_PNG, "PNG IDAT has invalid zlib compression method {}", (uint8_t)zlib_header.cm);
return BAN::Error::from_errno(EINVAL);
}
zlib_stream[0] = zlib_stream[0].slice(2);
}
uint64_t total_size = 0;
for (auto stream : zlib_stream)
total_size += stream.size();
dprintln_if(DEBUG_PNG, "PNG has {} byte zlib stream", total_size);
DeflateDecoder decoder(BAN::move(zlib_stream));
auto inflated_data = TRY(decoder.decode_stream());
dprintln_if(DEBUG_PNG, " uncompressed size {}", inflated_data.size());
dprintln_if(DEBUG_PNG, " compression ratio {}", (double)inflated_data.size() / total_size);
uint8_t bits_per_channel = ihdr.bit_depth;
uint8_t channels = 0;
switch (ihdr.colour_type)
{
case ColourType::Greyscale: channels = 1; break;
case ColourType::Truecolour: channels = 3; break;
case ColourType::IndexedColour: channels = 1; break;
case ColourType::GreyscaleAlpha: channels = 2; break;
case ColourType::TruecolourAlpha: channels = 4; break;
default:
ASSERT_NOT_REACHED();
}
const auto extract_channel =
[&](auto& bit_buffer) -> uint8_t
{
uint16_t tmp = MUST(bit_buffer.get_bits(bits_per_channel));
switch (bits_per_channel)
{
case 1: return tmp * 0xFF;
case 2: return tmp * 0xFF / 3;
case 4: return tmp * 0xFF / 15;
case 8: return tmp;
case 16: return tmp & 0xFF; // NOTE: stored in big endian
}
ASSERT_NOT_REACHED();
};
const auto extract_color =
[&](auto& bit_buffer) -> Image::Color
{
uint8_t tmp;
switch (ihdr.colour_type)
{
case ColourType::Greyscale:
tmp = extract_channel(bit_buffer);
return Image::Color {
.r = tmp,
.g = tmp,
.b = tmp,
.a = 0xFF
};
case ColourType::Truecolour:
return Image::Color {
.r = extract_channel(bit_buffer),
.g = extract_channel(bit_buffer),
.b = extract_channel(bit_buffer),
.a = 0xFF
};
case ColourType::IndexedColour:
return palette[MUST(bit_buffer.get_bits(bits_per_channel))];
case ColourType::GreyscaleAlpha:
tmp = extract_channel(bit_buffer);
return Image::Color {
.r = tmp,
.g = tmp,
.b = tmp,
.a = extract_channel(bit_buffer)
};
case ColourType::TruecolourAlpha:
return Image::Color {
.r = extract_channel(bit_buffer),
.g = extract_channel(bit_buffer),
.b = extract_channel(bit_buffer),
.a = extract_channel(bit_buffer)
};
}
ASSERT_NOT_REACHED();
};
constexpr auto paeth_predictor =
[](int16_t a, int16_t b, int16_t c) -> uint8_t
{
int16_t p = a + b - c;
int16_t pa = BAN::Math::abs(p - a);
int16_t pb = BAN::Math::abs(p - b);
int16_t pc = BAN::Math::abs(p - c);
if (pa <= pb && pa <= pc)
return a;
if (pb <= pc)
return b;
return c;
};
const uint64_t bytes_per_scanline = BAN::Math::div_round_up<uint64_t>(image_width * channels * bits_per_channel, 8);
const uint64_t pitch = bytes_per_scanline + 1;
if (inflated_data.size() < pitch * image_height)
{
dwarnln_if(DEBUG_PNG, "PNG does not contain enough image data");
return BAN::Error::from_errno(ENODATA);
}
BAN::Vector<uint8_t> zero_scanline;
TRY(zero_scanline.resize(bytes_per_scanline, 0));
BAN::Vector<Image::Color> color_bitmap;
TRY(color_bitmap.resize(image_width * image_height));
BAN::Vector<BAN::ConstByteSpan> inflated_data_wrapper;
TRY(inflated_data_wrapper.push_back({}));
const uint8_t filter_offset = (bits_per_channel < 8) ? 1 : channels * (bits_per_channel / 8);
for (uint64_t y = 0; y < image_height; y++)
{
auto scanline = inflated_data.slice((y - 0) * pitch + 1, bytes_per_scanline);
auto scanline_above = (y > 0) ? inflated_data.slice((y - 1) * pitch + 1, bytes_per_scanline) : BAN::ConstByteSpan(zero_scanline.span());
auto filter_type = static_cast<FilterType>(inflated_data[y * pitch]);
switch (filter_type)
{
case FilterType::None:
break;
case FilterType::Sub:
for (uint64_t x = filter_offset; x < bytes_per_scanline; x++)
scanline[x] += scanline[x - filter_offset];
break;
case FilterType::Up:
for (uint64_t x = 0; x < bytes_per_scanline; x++)
scanline[x] += scanline_above[x];
break;
case FilterType::Average:
for (uint8_t i = 0; i < filter_offset; i++)
scanline[i] += scanline_above[i] / 2;
for (uint64_t x = filter_offset; x < bytes_per_scanline; x++)
scanline[x] += ((uint16_t)scanline[x - filter_offset] + (uint16_t)scanline_above[x]) / 2;
break;
case FilterType::Paeth:
for (uint8_t i = 0; i < filter_offset; i++)
scanline[i] += paeth_predictor(0, scanline_above[i], 0);
for (uint64_t x = filter_offset; x < bytes_per_scanline; x++)
scanline[x] += paeth_predictor(scanline[x - filter_offset], scanline_above[x], scanline_above[x - filter_offset]);
break;
default:
dwarnln_if(DEBUG_PNG, "invalid filter type {}", static_cast<uint8_t>(filter_type));
return BAN::Error::from_errno(EINVAL);
}
inflated_data_wrapper[0] = scanline;
BitBuffer bit_buffer(inflated_data_wrapper);
for (uint64_t x = 0; x < image_width; x++)
color_bitmap[y * image_width + x] = extract_color(bit_buffer);
}
return TRY(BAN::UniqPtr<Image>::create(image_width, image_height, BAN::move(color_bitmap)));
}
}
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