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ladybird/Userland/Libraries/LibGfx/PNGLoader.cpp
Ryan Liptak b19f3b5106 LibGfx: Unfilter PNG data before unpacking it to RGBA 
The order of PNG compression is raw pixel data -> filter -> compress.
For decompression, the order is reversed, so that means uncompress ->
unfilter -> raw pixel data. Previously, the PNG decoder was converting
to raw pixel data before unfiltering, which was a problem when using
indexed color palettes, since each pixel's palette index could change
during unfiltering (e.g. it was unfiltering after already choosing
the color from the palette index). This was leading to 'Palette index
out of range' errors on files that both:

- Had scanlines with some sort of filtering
- Didn't use the full range of possible palette indices for their bit
  depth.

Also, because filtering now happens before converting to pixel data,
filtering acts on bytes instead of pixels, meaning that the
implementation of each filter type now maps much more directly to
the specification:

http://www.libpng.org/pub/png/spec/1.2/PNG-Filters.html
2022-08-18 11:12:59 +01:00

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/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2022, the SerenityOS developers.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Array.h>
#include <AK/Debug.h>
#include <AK/Endian.h>
#include <AK/Vector.h>
#include <LibCompress/Zlib.h>
#include <LibGfx/PNGLoader.h>
#include <LibGfx/PNGShared.h>
#include <string.h>
#ifdef __serenity__
# include <LibCompress/Deflate.h>
#endif
namespace Gfx {
struct PNG_IHDR {
NetworkOrdered<u32> width;
NetworkOrdered<u32> height;
u8 bit_depth { 0 };
PNG::ColorType color_type { 0 };
u8 compression_method { 0 };
u8 filter_method { 0 };
u8 interlace_method { 0 };
};
static_assert(AssertSize<PNG_IHDR, 13>());
struct Scanline {
PNG::FilterType filter;
ReadonlyBytes data {};
};
struct [[gnu::packed]] PaletteEntry {
u8 r;
u8 g;
u8 b;
// u8 a;
};
template<typename T>
struct [[gnu::packed]] Tuple {
T gray;
T a;
};
template<typename T>
struct [[gnu::packed]] Triplet {
T r;
T g;
T b;
bool operator==(Triplet const& other) const = default;
};
template<typename T>
struct [[gnu::packed]] Quartet {
T r;
T g;
T b;
T a;
};
enum PngInterlaceMethod {
Null = 0,
Adam7 = 1
};
struct PNGLoadingContext {
enum State {
NotDecoded = 0,
Error,
HeaderDecoded,
SizeDecoded,
ChunksDecoded,
BitmapDecoded,
};
State state { State::NotDecoded };
u8 const* data { nullptr };
size_t data_size { 0 };
int width { -1 };
int height { -1 };
u8 bit_depth { 0 };
PNG::ColorType color_type { 0 };
u8 compression_method { 0 };
u8 filter_method { 0 };
u8 interlace_method { 0 };
u8 channels { 0 };
bool has_seen_zlib_header { false };
bool has_alpha() const { return to_underlying(color_type) & 4 || palette_transparency_data.size() > 0; }
Vector<Scanline> scanlines;
ByteBuffer unfiltered_data;
RefPtr<Gfx::Bitmap> bitmap;
ByteBuffer* decompression_buffer { nullptr };
Vector<u8> compressed_data;
Vector<PaletteEntry> palette_data;
Vector<u8> palette_transparency_data;
Checked<int> compute_row_size_for_width(int width)
{
Checked<int> row_size = width;
row_size *= channels;
row_size *= bit_depth;
row_size += 7;
row_size /= 8;
if (row_size.has_overflow()) {
dbgln("PNG too large, integer overflow while computing row size");
state = State::Error;
}
return row_size;
}
};
class Streamer {
public:
Streamer(u8 const* data, size_t size)
: m_data_ptr(data)
, m_size_remaining(size)
{
}
template<typename T>
bool read(T& value)
{
if (m_size_remaining < sizeof(T))
return false;
value = *((NetworkOrdered<T> const*)m_data_ptr);
m_data_ptr += sizeof(T);
m_size_remaining -= sizeof(T);
return true;
}
bool read_bytes(u8* buffer, size_t count)
{
if (m_size_remaining < count)
return false;
memcpy(buffer, m_data_ptr, count);
m_data_ptr += count;
m_size_remaining -= count;
return true;
}
bool wrap_bytes(ReadonlyBytes& buffer, size_t count)
{
if (m_size_remaining < count)
return false;
buffer = ReadonlyBytes { m_data_ptr, count };
m_data_ptr += count;
m_size_remaining -= count;
return true;
}
bool at_end() const { return !m_size_remaining; }
private:
u8 const* m_data_ptr { nullptr };
size_t m_size_remaining { 0 };
};
static bool process_chunk(Streamer&, PNGLoadingContext& context);
union [[gnu::packed]] Pixel {
ARGB32 rgba { 0 };
u8 v[4];
struct {
u8 r;
u8 g;
u8 b;
u8 a;
};
};
static_assert(AssertSize<Pixel, 4>());
static void unfilter_scanline(PNG::FilterType filter, Bytes scanline_data, ReadonlyBytes previous_scanlines_data, u8 bytes_per_complete_pixel)
{
VERIFY(filter != PNG::FilterType::None);
switch (filter) {
case PNG::FilterType::Sub:
for (size_t i = 0; i < scanline_data.size(); ++i) {
u8 left = (i < bytes_per_complete_pixel) ? 0 : scanline_data[i - bytes_per_complete_pixel];
scanline_data[i] += left;
}
break;
case PNG::FilterType::Up:
for (size_t i = 0; i < scanline_data.size(); ++i) {
u8 above = previous_scanlines_data[i];
scanline_data[i] += above;
}
break;
case PNG::FilterType::Average:
for (size_t i = 0; i < scanline_data.size(); ++i) {
u32 left = (i < bytes_per_complete_pixel) ? 0 : scanline_data[i - bytes_per_complete_pixel];
u32 above = previous_scanlines_data[i];
u8 average = (left + above) / 2;
scanline_data[i] += average;
}
break;
case PNG::FilterType::Paeth:
for (size_t i = 0; i < scanline_data.size(); ++i) {
u8 left = (i < bytes_per_complete_pixel) ? 0 : scanline_data[i - bytes_per_complete_pixel];
u8 above = previous_scanlines_data[i];
u8 upper_left = (i < bytes_per_complete_pixel) ? 0 : previous_scanlines_data[i - bytes_per_complete_pixel];
i32 predictor = left + above - upper_left;
u32 predictor_left = abs(predictor - left);
u32 predictor_above = abs(predictor - above);
u32 predictor_upper_left = abs(predictor - upper_left);
u8 nearest;
if (predictor_left <= predictor_above && predictor_left <= predictor_upper_left) {
nearest = left;
} else if (predictor_above <= predictor_upper_left) {
nearest = above;
} else {
nearest = upper_left;
}
scanline_data[i] += nearest;
}
break;
default:
VERIFY_NOT_REACHED();
}
}
template<typename T>
ALWAYS_INLINE static void unpack_grayscale_without_alpha(PNGLoadingContext& context)
{
for (int y = 0; y < context.height; ++y) {
auto* gray_values = reinterpret_cast<const T*>(context.scanlines[y].data.data());
for (int i = 0; i < context.width; ++i) {
auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
pixel.r = gray_values[i];
pixel.g = gray_values[i];
pixel.b = gray_values[i];
pixel.a = 0xff;
}
}
}
template<typename T>
ALWAYS_INLINE static void unpack_grayscale_with_alpha(PNGLoadingContext& context)
{
for (int y = 0; y < context.height; ++y) {
auto* tuples = reinterpret_cast<Tuple<T> const*>(context.scanlines[y].data.data());
for (int i = 0; i < context.width; ++i) {
auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
pixel.r = tuples[i].gray;
pixel.g = tuples[i].gray;
pixel.b = tuples[i].gray;
pixel.a = tuples[i].a;
}
}
}
template<typename T>
ALWAYS_INLINE static void unpack_triplets_without_alpha(PNGLoadingContext& context)
{
for (int y = 0; y < context.height; ++y) {
auto* triplets = reinterpret_cast<Triplet<T> const*>(context.scanlines[y].data.data());
for (int i = 0; i < context.width; ++i) {
auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
pixel.r = triplets[i].r;
pixel.g = triplets[i].g;
pixel.b = triplets[i].b;
pixel.a = 0xff;
}
}
}
template<typename T>
ALWAYS_INLINE static void unpack_triplets_with_transparency_value(PNGLoadingContext& context, Triplet<T> transparency_value)
{
for (int y = 0; y < context.height; ++y) {
auto* triplets = reinterpret_cast<Triplet<T> const*>(context.scanlines[y].data.data());
for (int i = 0; i < context.width; ++i) {
auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
pixel.r = triplets[i].r;
pixel.g = triplets[i].g;
pixel.b = triplets[i].b;
if (triplets[i] == transparency_value)
pixel.a = 0x00;
else
pixel.a = 0xff;
}
}
}
NEVER_INLINE FLATTEN static ErrorOr<void> unfilter(PNGLoadingContext& context)
{
// First unfilter the scanlines:
// FIXME: Instead of creating a separate buffer for the scanlines that need to be
// mutated, the mutation could be done in place (if the data was non-const).
size_t bytes_per_scanline = context.scanlines[0].data.size();
size_t bytes_needed_for_all_unfiltered_scanlines = 0;
for (int y = 0; y < context.height; ++y) {
if (context.scanlines[y].filter != PNG::FilterType::None) {
bytes_needed_for_all_unfiltered_scanlines += bytes_per_scanline;
}
}
context.unfiltered_data = TRY(ByteBuffer::create_uninitialized(bytes_needed_for_all_unfiltered_scanlines));
// From section 6.3 of http://www.libpng.org/pub/png/spec/1.2/PNG-Filters.html
// "bpp is defined as the number of bytes per complete pixel, rounding up to one.
// For example, for color type 2 with a bit depth of 16, bpp is equal to 6
// (three samples, two bytes per sample); for color type 0 with a bit depth of 2,
// bpp is equal to 1 (rounding up); for color type 4 with a bit depth of 16, bpp
// is equal to 4 (two-byte grayscale sample, plus two-byte alpha sample)."
u8 bytes_per_complete_pixel = (context.bit_depth + 7) / 8 * context.channels;
u8 dummy_scanline_bytes[bytes_per_scanline];
memset(dummy_scanline_bytes, 0, sizeof(dummy_scanline_bytes));
auto previous_scanlines_data = ReadonlyBytes { dummy_scanline_bytes, sizeof(dummy_scanline_bytes) };
for (int y = 0, data_start = 0; y < context.height; ++y) {
if (context.scanlines[y].filter != PNG::FilterType::None) {
auto scanline_data_slice = context.unfiltered_data.bytes().slice(data_start, bytes_per_scanline);
// Copy the current values over and set the scanline's data to the to-be-mutated slice
context.scanlines[y].data.copy_to(scanline_data_slice);
context.scanlines[y].data = scanline_data_slice;
unfilter_scanline(context.scanlines[y].filter, scanline_data_slice, previous_scanlines_data, bytes_per_complete_pixel);
data_start += bytes_per_scanline;
}
previous_scanlines_data = context.scanlines[y].data;
}
// Now unpack the scanlines to RGBA:
switch (context.color_type) {
case PNG::ColorType::Greyscale:
if (context.bit_depth == 8) {
unpack_grayscale_without_alpha<u8>(context);
} else if (context.bit_depth == 16) {
unpack_grayscale_without_alpha<u16>(context);
} else if (context.bit_depth == 1 || context.bit_depth == 2 || context.bit_depth == 4) {
auto bit_depth_squared = context.bit_depth * context.bit_depth;
auto pixels_per_byte = 8 / context.bit_depth;
auto mask = (1 << context.bit_depth) - 1;
for (int y = 0; y < context.height; ++y) {
auto* gray_values = context.scanlines[y].data.data();
for (int x = 0; x < context.width; ++x) {
auto bit_offset = (8 - context.bit_depth) - (context.bit_depth * (x % pixels_per_byte));
auto value = (gray_values[x / pixels_per_byte] >> bit_offset) & mask;
auto& pixel = (Pixel&)context.bitmap->scanline(y)[x];
pixel.r = value * (0xff / bit_depth_squared);
pixel.g = value * (0xff / bit_depth_squared);
pixel.b = value * (0xff / bit_depth_squared);
pixel.a = 0xff;
}
}
} else {
VERIFY_NOT_REACHED();
}
break;
case PNG::ColorType::GreyscaleWithAlpha:
if (context.bit_depth == 8) {
unpack_grayscale_with_alpha<u8>(context);
} else if (context.bit_depth == 16) {
unpack_grayscale_with_alpha<u16>(context);
} else {
VERIFY_NOT_REACHED();
}
break;
case PNG::ColorType::Truecolor:
if (context.palette_transparency_data.size() == 6) {
if (context.bit_depth == 8) {
unpack_triplets_with_transparency_value<u8>(context, Triplet<u8> { context.palette_transparency_data[0], context.palette_transparency_data[2], context.palette_transparency_data[4] });
} else if (context.bit_depth == 16) {
u16 tr = context.palette_transparency_data[0] | context.palette_transparency_data[1] << 8;
u16 tg = context.palette_transparency_data[2] | context.palette_transparency_data[3] << 8;
u16 tb = context.palette_transparency_data[4] | context.palette_transparency_data[5] << 8;
unpack_triplets_with_transparency_value<u16>(context, Triplet<u16> { tr, tg, tb });
} else {
VERIFY_NOT_REACHED();
}
} else {
if (context.bit_depth == 8)
unpack_triplets_without_alpha<u8>(context);
else if (context.bit_depth == 16)
unpack_triplets_without_alpha<u16>(context);
else
VERIFY_NOT_REACHED();
}
break;
case PNG::ColorType::TruecolorWithAlpha:
if (context.bit_depth == 8) {
for (int y = 0; y < context.height; ++y) {
memcpy(context.bitmap->scanline(y), context.scanlines[y].data.data(), context.scanlines[y].data.size());
}
} else if (context.bit_depth == 16) {
for (int y = 0; y < context.height; ++y) {
auto* quartets = reinterpret_cast<Quartet<u16> const*>(context.scanlines[y].data.data());
for (int i = 0; i < context.width; ++i) {
auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
pixel.r = quartets[i].r & 0xFF;
pixel.g = quartets[i].g & 0xFF;
pixel.b = quartets[i].b & 0xFF;
pixel.a = quartets[i].a & 0xFF;
}
}
} else {
VERIFY_NOT_REACHED();
}
break;
case PNG::ColorType::IndexedColor:
if (context.bit_depth == 8) {
for (int y = 0; y < context.height; ++y) {
auto* palette_index = context.scanlines[y].data.data();
for (int i = 0; i < context.width; ++i) {
auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
if (palette_index[i] >= context.palette_data.size())
return Error::from_string_literal("PNGImageDecoderPlugin: Palette index out of range");
auto& color = context.palette_data.at((int)palette_index[i]);
auto transparency = context.palette_transparency_data.size() >= palette_index[i] + 1u
? context.palette_transparency_data.data()[palette_index[i]]
: 0xff;
pixel.r = color.r;
pixel.g = color.g;
pixel.b = color.b;
pixel.a = transparency;
}
}
} else if (context.bit_depth == 1 || context.bit_depth == 2 || context.bit_depth == 4) {
auto pixels_per_byte = 8 / context.bit_depth;
auto mask = (1 << context.bit_depth) - 1;
for (int y = 0; y < context.height; ++y) {
auto* palette_indices = context.scanlines[y].data.data();
for (int i = 0; i < context.width; ++i) {
auto bit_offset = (8 - context.bit_depth) - (context.bit_depth * (i % pixels_per_byte));
auto palette_index = (palette_indices[i / pixels_per_byte] >> bit_offset) & mask;
auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
if ((size_t)palette_index >= context.palette_data.size())
return Error::from_string_literal("PNGImageDecoderPlugin: Palette index out of range");
auto& color = context.palette_data.at(palette_index);
auto transparency = context.palette_transparency_data.size() >= palette_index + 1u
? context.palette_transparency_data.data()[palette_index]
: 0xff;
pixel.r = color.r;
pixel.g = color.g;
pixel.b = color.b;
pixel.a = transparency;
}
}
} else {
VERIFY_NOT_REACHED();
}
break;
default:
VERIFY_NOT_REACHED();
break;
}
// Swap r and b values:
for (int y = 0; y < context.height; ++y) {
auto* pixels = (Pixel*)context.bitmap->scanline(y);
for (int i = 0; i < context.bitmap->width(); ++i) {
auto& x = pixels[i];
swap(x.r, x.b);
}
}
return {};
}
static bool decode_png_header(PNGLoadingContext& context)
{
if (context.state >= PNGLoadingContext::HeaderDecoded)
return true;
if (!context.data || context.data_size < sizeof(PNG::header)) {
dbgln_if(PNG_DEBUG, "Missing PNG header");
context.state = PNGLoadingContext::State::Error;
return false;
}
if (memcmp(context.data, PNG::header.span().data(), sizeof(PNG::header)) != 0) {
dbgln_if(PNG_DEBUG, "Invalid PNG header");
context.state = PNGLoadingContext::State::Error;
return false;
}
context.state = PNGLoadingContext::HeaderDecoded;
return true;
}
static bool decode_png_size(PNGLoadingContext& context)
{
if (context.state >= PNGLoadingContext::SizeDecoded)
return true;
if (context.state < PNGLoadingContext::HeaderDecoded) {
if (!decode_png_header(context))
return false;
}
u8 const* data_ptr = context.data + sizeof(PNG::header);
size_t data_remaining = context.data_size - sizeof(PNG::header);
Streamer streamer(data_ptr, data_remaining);
while (!streamer.at_end()) {
if (!process_chunk(streamer, context)) {
context.state = PNGLoadingContext::State::Error;
return false;
}
if (context.width && context.height) {
context.state = PNGLoadingContext::State::SizeDecoded;
return true;
}
}
return false;
}
static bool decode_png_chunks(PNGLoadingContext& context)
{
if (context.state >= PNGLoadingContext::State::ChunksDecoded)
return true;
if (context.state < PNGLoadingContext::HeaderDecoded) {
if (!decode_png_header(context))
return false;
}
u8 const* data_ptr = context.data + sizeof(PNG::header);
int data_remaining = context.data_size - sizeof(PNG::header);
context.compressed_data.ensure_capacity(context.data_size);
Streamer streamer(data_ptr, data_remaining);
while (!streamer.at_end()) {
if (!process_chunk(streamer, context)) {
// Ignore failed chunk and just consider chunk decoding being done.
// decode_png_bitmap() will check whether we got all required ones anyway.
break;
}
}
context.state = PNGLoadingContext::State::ChunksDecoded;
return true;
}
static ErrorOr<void> decode_png_bitmap_simple(PNGLoadingContext& context)
{
Streamer streamer(context.decompression_buffer->data(), context.decompression_buffer->size());
for (int y = 0; y < context.height; ++y) {
PNG::FilterType filter;
if (!streamer.read(filter)) {
context.state = PNGLoadingContext::State::Error;
return Error::from_string_literal("PNGImageDecoderPlugin: Decoding failed");
}
if (to_underlying(filter) > 4) {
context.state = PNGLoadingContext::State::Error;
return Error::from_string_literal("PNGImageDecoderPlugin: Invalid PNG filter");
}
context.scanlines.append({ filter });
auto& scanline_buffer = context.scanlines.last().data;
auto row_size = context.compute_row_size_for_width(context.width);
if (row_size.has_overflow())
return Error::from_string_literal("PNGImageDecoderPlugin: Row size overflow");
if (!streamer.wrap_bytes(scanline_buffer, row_size.value())) {
context.state = PNGLoadingContext::State::Error;
return Error::from_string_literal("PNGImageDecoderPlugin: Decoding failed");
}
}
context.bitmap = TRY(Bitmap::try_create(context.has_alpha() ? BitmapFormat::BGRA8888 : BitmapFormat::BGRx8888, { context.width, context.height }));
return unfilter(context);
}
static int adam7_height(PNGLoadingContext& context, int pass)
{
switch (pass) {
case 1:
return (context.height + 7) / 8;
case 2:
return (context.height + 7) / 8;
case 3:
return (context.height + 3) / 8;
case 4:
return (context.height + 3) / 4;
case 5:
return (context.height + 1) / 4;
case 6:
return (context.height + 1) / 2;
case 7:
return context.height / 2;
default:
VERIFY_NOT_REACHED();
}
}
static int adam7_width(PNGLoadingContext& context, int pass)
{
switch (pass) {
case 1:
return (context.width + 7) / 8;
case 2:
return (context.width + 3) / 8;
case 3:
return (context.width + 3) / 4;
case 4:
return (context.width + 1) / 4;
case 5:
return (context.width + 1) / 2;
case 6:
return context.width / 2;
case 7:
return context.width;
default:
VERIFY_NOT_REACHED();
}
}
// Index 0 unused (non-interlaced case)
static int adam7_starty[8] = { 0, 0, 0, 4, 0, 2, 0, 1 };
static int adam7_startx[8] = { 0, 0, 4, 0, 2, 0, 1, 0 };
static int adam7_stepy[8] = { 1, 8, 8, 8, 4, 4, 2, 2 };
static int adam7_stepx[8] = { 1, 8, 8, 4, 4, 2, 2, 1 };
static ErrorOr<void> decode_adam7_pass(PNGLoadingContext& context, Streamer& streamer, int pass)
{
PNGLoadingContext subimage_context;
subimage_context.width = adam7_width(context, pass);
subimage_context.height = adam7_height(context, pass);
subimage_context.channels = context.channels;
subimage_context.color_type = context.color_type;
subimage_context.palette_data = context.palette_data;
subimage_context.palette_transparency_data = context.palette_transparency_data;
subimage_context.bit_depth = context.bit_depth;
subimage_context.filter_method = context.filter_method;
// For small images, some passes might be empty
if (!subimage_context.width || !subimage_context.height)
return {};
subimage_context.scanlines.clear_with_capacity();
for (int y = 0; y < subimage_context.height; ++y) {
PNG::FilterType filter;
if (!streamer.read(filter)) {
context.state = PNGLoadingContext::State::Error;
return Error::from_string_literal("PNGImageDecoderPlugin: Decoding failed");
}
if (to_underlying(filter) > 4) {
context.state = PNGLoadingContext::State::Error;
return Error::from_string_literal("PNGImageDecoderPlugin: Invalid PNG filter");
}
subimage_context.scanlines.append({ filter });
auto& scanline_buffer = subimage_context.scanlines.last().data;
auto row_size = context.compute_row_size_for_width(subimage_context.width);
if (row_size.has_overflow())
return Error::from_string_literal("PNGImageDecoderPlugin: Row size overflow");
if (!streamer.wrap_bytes(scanline_buffer, row_size.value())) {
context.state = PNGLoadingContext::State::Error;
return Error::from_string_literal("PNGImageDecoderPlugin: Decoding failed");
}
}
subimage_context.bitmap = TRY(Bitmap::try_create(context.bitmap->format(), { subimage_context.width, subimage_context.height }));
TRY(unfilter(subimage_context));
// Copy the subimage data into the main image according to the pass pattern
for (int y = 0, dy = adam7_starty[pass]; y < subimage_context.height && dy < context.height; ++y, dy += adam7_stepy[pass]) {
for (int x = 0, dx = adam7_startx[pass]; x < subimage_context.width && dy < context.width; ++x, dx += adam7_stepx[pass]) {
context.bitmap->set_pixel(dx, dy, subimage_context.bitmap->get_pixel(x, y));
}
}
return {};
}
static ErrorOr<void> decode_png_adam7(PNGLoadingContext& context)
{
Streamer streamer(context.decompression_buffer->data(), context.decompression_buffer->size());
context.bitmap = TRY(Bitmap::try_create(context.has_alpha() ? BitmapFormat::BGRA8888 : BitmapFormat::BGRx8888, { context.width, context.height }));
for (int pass = 1; pass <= 7; ++pass)
TRY(decode_adam7_pass(context, streamer, pass));
return {};
}
static ErrorOr<void> decode_png_bitmap(PNGLoadingContext& context)
{
if (context.state < PNGLoadingContext::State::ChunksDecoded) {
if (!decode_png_chunks(context))
return Error::from_string_literal("PNGImageDecoderPlugin: Decoding failed");
}
if (context.state >= PNGLoadingContext::State::BitmapDecoded)
return {};
if (context.width == -1 || context.height == -1)
return Error::from_string_literal("PNGImageDecoderPlugin: Didn't see an IHDR chunk.");
if (context.color_type == PNG::ColorType::IndexedColor && context.palette_data.is_empty())
return Error::from_string_literal("PNGImageDecoderPlugin: Didn't see a PLTE chunk for a palletized image, or it was empty.");
auto result = Compress::Zlib::decompress_all(context.compressed_data.span());
if (!result.has_value()) {
context.state = PNGLoadingContext::State::Error;
return Error::from_string_literal("PNGImageDecoderPlugin: Decompression failed");
}
context.decompression_buffer = &result.value();
context.compressed_data.clear();
context.scanlines.ensure_capacity(context.height);
switch (context.interlace_method) {
case PngInterlaceMethod::Null:
TRY(decode_png_bitmap_simple(context));
break;
case PngInterlaceMethod::Adam7:
TRY(decode_png_adam7(context));
break;
default:
context.state = PNGLoadingContext::State::Error;
return Error::from_string_literal("PNGImageDecoderPlugin: Invalid interlace method");
}
context.decompression_buffer = nullptr;
context.state = PNGLoadingContext::State::BitmapDecoded;
return {};
}
static bool is_valid_compression_method(u8 compression_method)
{
return compression_method == 0;
}
static bool is_valid_filter_method(u8 filter_method)
{
return filter_method == 0;
}
static bool process_IHDR(ReadonlyBytes data, PNGLoadingContext& context)
{
if (data.size() < (int)sizeof(PNG_IHDR))
return false;
auto& ihdr = *(const PNG_IHDR*)data.data();
if (ihdr.width > maximum_width_for_decoded_images || ihdr.height > maximum_height_for_decoded_images) {
dbgln("This PNG is too large for comfort: {}x{}", (u32)ihdr.width, (u32)ihdr.height);
return false;
}
if (!is_valid_compression_method(ihdr.compression_method)) {
dbgln("PNG has invalid compression method {}", ihdr.compression_method);
return false;
}
if (!is_valid_filter_method(ihdr.filter_method)) {
dbgln("PNG has invalid filter method {}", ihdr.filter_method);
return false;
}
context.width = ihdr.width;
context.height = ihdr.height;
context.bit_depth = ihdr.bit_depth;
context.color_type = ihdr.color_type;
context.compression_method = ihdr.compression_method;
context.filter_method = ihdr.filter_method;
context.interlace_method = ihdr.interlace_method;
dbgln_if(PNG_DEBUG, "PNG: {}x{} ({} bpp)", context.width, context.height, context.bit_depth);
dbgln_if(PNG_DEBUG, " Color type: {}", to_underlying(context.color_type));
dbgln_if(PNG_DEBUG, "Compress Method: {}", context.compression_method);
dbgln_if(PNG_DEBUG, " Filter Method: {}", context.filter_method);
dbgln_if(PNG_DEBUG, " Interlace type: {}", context.interlace_method);
if (context.interlace_method != PngInterlaceMethod::Null && context.interlace_method != PngInterlaceMethod::Adam7) {
dbgln_if(PNG_DEBUG, "PNGLoader::process_IHDR: unknown interlace method: {}", context.interlace_method);
return false;
}
switch (context.color_type) {
case PNG::ColorType::Greyscale:
if (context.bit_depth != 1 && context.bit_depth != 2 && context.bit_depth != 4 && context.bit_depth != 8 && context.bit_depth != 16)
return false;
context.channels = 1;
break;
case PNG::ColorType::GreyscaleWithAlpha:
if (context.bit_depth != 8 && context.bit_depth != 16)
return false;
context.channels = 2;
break;
case PNG::ColorType::Truecolor:
if (context.bit_depth != 8 && context.bit_depth != 16)
return false;
context.channels = 3;
break;
case PNG::ColorType::IndexedColor:
if (context.bit_depth != 1 && context.bit_depth != 2 && context.bit_depth != 4 && context.bit_depth != 8)
return false;
context.channels = 1;
break;
case PNG::ColorType::TruecolorWithAlpha:
if (context.bit_depth != 8 && context.bit_depth != 16)
return false;
context.channels = 4;
break;
default:
return false;
}
return true;
}
static bool process_IDAT(ReadonlyBytes data, PNGLoadingContext& context)
{
context.compressed_data.append(data.data(), data.size());
return true;
}
static bool process_PLTE(ReadonlyBytes data, PNGLoadingContext& context)
{
context.palette_data.append((PaletteEntry const*)data.data(), data.size() / 3);
return true;
}
static bool process_tRNS(ReadonlyBytes data, PNGLoadingContext& context)
{
switch (context.color_type) {
case PNG::ColorType::Greyscale:
case PNG::ColorType::Truecolor:
case PNG::ColorType::IndexedColor:
context.palette_transparency_data.append(data.data(), data.size());
break;
default:
break;
}
return true;
}
static bool process_chunk(Streamer& streamer, PNGLoadingContext& context)
{
u32 chunk_size;
if (!streamer.read(chunk_size)) {
dbgln_if(PNG_DEBUG, "Bail at chunk_size");
return false;
}
u8 chunk_type[5];
chunk_type[4] = '\0';
if (!streamer.read_bytes(chunk_type, 4)) {
dbgln_if(PNG_DEBUG, "Bail at chunk_type");
return false;
}
ReadonlyBytes chunk_data;
if (!streamer.wrap_bytes(chunk_data, chunk_size)) {
dbgln_if(PNG_DEBUG, "Bail at chunk_data");
return false;
}
u32 chunk_crc;
if (!streamer.read(chunk_crc)) {
dbgln_if(PNG_DEBUG, "Bail at chunk_crc");
return false;
}
dbgln_if(PNG_DEBUG, "Chunk type: '{}', size: {}, crc: {:x}", chunk_type, chunk_size, chunk_crc);
if (!strcmp((char const*)chunk_type, "IHDR"))
return process_IHDR(chunk_data, context);
if (!strcmp((char const*)chunk_type, "IDAT"))
return process_IDAT(chunk_data, context);
if (!strcmp((char const*)chunk_type, "PLTE"))
return process_PLTE(chunk_data, context);
if (!strcmp((char const*)chunk_type, "tRNS"))
return process_tRNS(chunk_data, context);
return true;
}
PNGImageDecoderPlugin::PNGImageDecoderPlugin(u8 const* data, size_t size)
{
m_context = make<PNGLoadingContext>();
m_context->data = data;
m_context->data_size = size;
}
PNGImageDecoderPlugin::~PNGImageDecoderPlugin() = default;
IntSize PNGImageDecoderPlugin::size()
{
if (m_context->state == PNGLoadingContext::State::Error)
return {};
if (m_context->state < PNGLoadingContext::State::SizeDecoded) {
bool success = decode_png_size(*m_context);
if (!success)
return {};
}
return { m_context->width, m_context->height };
}
void PNGImageDecoderPlugin::set_volatile()
{
if (m_context->bitmap)
m_context->bitmap->set_volatile();
}
bool PNGImageDecoderPlugin::set_nonvolatile(bool& was_purged)
{
if (!m_context->bitmap)
return false;
return m_context->bitmap->set_nonvolatile(was_purged);
}
bool PNGImageDecoderPlugin::sniff()
{
return decode_png_header(*m_context);
}
bool PNGImageDecoderPlugin::is_animated()
{
return false;
}
size_t PNGImageDecoderPlugin::loop_count()
{
return 0;
}
size_t PNGImageDecoderPlugin::frame_count()
{
return 1;
}
ErrorOr<ImageFrameDescriptor> PNGImageDecoderPlugin::frame(size_t index)
{
if (index > 0)
return Error::from_string_literal("PNGImageDecoderPlugin: Invalid frame index");
if (m_context->state == PNGLoadingContext::State::Error)
return Error::from_string_literal("PNGImageDecoderPlugin: Decoding failed");
if (m_context->state < PNGLoadingContext::State::BitmapDecoded) {
// NOTE: This forces the chunk decoding to happen.
TRY(decode_png_bitmap(*m_context));
}
VERIFY(m_context->bitmap);
return ImageFrameDescriptor { m_context->bitmap, 0 };
}
}
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