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/* SPDX-License-Identifier: GPL-2.0-or-later
* Copyright 2008 Blender Foundation. All rights reserved. */
/** \file
* \ingroup blendthumb
*
* Expose #blendthumb_create_png_data_from_thumb that creates the PNG data
* but does not write it to a file.
*/
#include <cstring>
#include <optional>
#include <zlib.h>
#include "blendthumb.hh"
#include "BLI_endian_defines.h"
#include "BLI_endian_switch.h"
#include "BLI_vector.hh"
static void png_extend_native_int32(blender::Vector<uint8_t> &output, int32_t data)
{
if (ENDIAN_ORDER == L_ENDIAN) {
BLI_endian_switch_int32(&data);
}
output.extend_unchecked(blender::Span((uint8_t *)&data, 4));
}
/** The number of bytes each chunk uses on top of the data that's written. */
#define PNG_CHUNK_EXTRA 12
static void png_chunk_create(blender::Vector<uint8_t> &output,
const uint32_t tag,
const blender::Vector<uint8_t> &data)
{
uint32_t crc = crc32(0, nullptr, 0);
crc = crc32(crc, (uint8_t *)&tag, sizeof(tag));
crc = crc32(crc, (uint8_t *)data.data(), data.size());
png_extend_native_int32(output, data.size());
output.extend_unchecked(blender::Span((uint8_t *)&tag, sizeof(tag)));
output.extend_unchecked(data);
png_extend_native_int32(output, crc);
}
static blender::Vector<uint8_t> filtered_rows_from_thumb(const Thumbnail *thumb)
{
/* In the image data sent to the compression step, each scan-line is preceded by a filter type
* byte containing the numeric code of the filter algorithm used for that scan-line. */
const size_t line_size = thumb->width * 4;
blender::Vector<uint8_t> filtered{};
size_t final_size = thumb->height * (line_size + 1);
filtered.reserve(final_size);
for (int i = 0; i < thumb->height; i++) {
filtered.append_unchecked(0x00);
filtered.extend_unchecked(blender::Span(&thumb->data[i * line_size], line_size));
}
BLI_assert(final_size == filtered.size());
return filtered;
}
static std::optional<blender::Vector<uint8_t>> zlib_compress(const blender::Vector<uint8_t> &data)
{
unsigned long uncompressed_size = data.size();
uLongf compressed_size = compressBound(uncompressed_size);
blender::Vector<uint8_t> compressed(compressed_size, 0x00);
int return_value = compress2((uchar *)compressed.data(),
&compressed_size,
(uchar *)data.data(),
uncompressed_size,
Z_NO_COMPRESSION);
if (return_value != Z_OK) {
/* Something went wrong with compression of data. */
return std::nullopt;
}
compressed.resize(compressed_size);
return compressed;
}
std::optional<blender::Vector<uint8_t>> blendthumb_create_png_data_from_thumb(
const Thumbnail *thumb)
{
if (thumb->data.is_empty()) {
return std::nullopt;
}
/* Create `IDAT` chunk data. */
blender::Vector<uint8_t> image_data{};
{
auto image_data_opt = zlib_compress(filtered_rows_from_thumb(thumb));
if (image_data_opt == std::nullopt) {
return std::nullopt;
}
image_data = *image_data_opt;
}
/* Create the IHDR chunk data. */
blender::Vector<uint8_t> ihdr_data{};
{
const size_t ihdr_data_final_size = 4 + 4 + 5;
ihdr_data.reserve(ihdr_data_final_size);
png_extend_native_int32(ihdr_data, thumb->width);
png_extend_native_int32(ihdr_data, thumb->height);
ihdr_data.extend_unchecked({
0x08, /* Bit Depth. */
0x06, /* Color Type. */
0x00, /* Compression method. */
0x00, /* Filter method. */
0x00, /* Interlace method. */
});
BLI_assert((size_t)ihdr_data.size() == ihdr_data_final_size);
}
/* Join it all together to create a PNG image. */
blender::Vector<uint8_t> png_buf{};
{
const size_t png_buf_final_size = (
/* Header. */
8 +
/* `IHDR` chunk. */
(ihdr_data.size() + PNG_CHUNK_EXTRA) +
/* `IDAT` chunk. */
(image_data.size() + PNG_CHUNK_EXTRA) +
/* `IEND` chunk. */
PNG_CHUNK_EXTRA);
png_buf.reserve(png_buf_final_size);
/* This is the standard PNG file header. Every PNG file starts with it. */
png_buf.extend_unchecked({0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A});
png_chunk_create(png_buf, MAKE_ID('I', 'H', 'D', 'R'), ihdr_data);
png_chunk_create(png_buf, MAKE_ID('I', 'D', 'A', 'T'), image_data);
png_chunk_create(png_buf, MAKE_ID('I', 'E', 'N', 'D'), {});
BLI_assert((size_t)png_buf.size() == png_buf_final_size);
}
return png_buf;
}
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