minetest/src/util/png.cpp

/*
Minetest
Copyright (C) 2021 hecks

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

#include "png.h"
#include <string>
#include <sstream>
#include <zlib.h>
#include <cassert>
#include "util/serialize.h"
#include "serialization.h"
#include "irrlichttypes.h"

static void writeChunk(std::ostringstream &target, const std::string &chunk_str)
{
	assert(chunk_str.size() >= 4);
	assert(chunk_str.size() - 4 < U32_MAX);
	writeU32(target, chunk_str.size() - 4); // Write length minus the identifier
	target << chunk_str;
	writeU32(target, crc32(0,(const u8*)chunk_str.data(), chunk_str.size()));
}

std::string encodePNG(const u8 *data, u32 width, u32 height, s32 compression)
{
	std::ostringstream file(std::ios::binary);
	file << "\x89PNG\r\n\x1a\n";

	{
		std::ostringstream IHDR(std::ios::binary);
		IHDR << "IHDR";
		writeU32(IHDR, width);
		writeU32(IHDR, height);
		// 8 bpp, color type 6 (RGBA)
		IHDR.write("\x08\x06\x00\x00\x00", 5);
		writeChunk(file, IHDR.str());
	}

	{
		std::ostringstream IDAT(std::ios::binary);
		IDAT << "IDAT";
		std::ostringstream scanlines(std::ios::binary);
		for(u32 i = 0; i < height; i++) {
			scanlines.write("\x00", 1); // Null predictor
			scanlines.write((const char*) data + width * 4 * i, width * 4);
		}
		compressZlib(scanlines.str(), IDAT, compression);
		writeChunk(file, IDAT.str());
	}

	file.write("\x00\x00\x00\x00IEND\xae\x42\x60\x82", 12);

	return file.str();
}