Add a simple PNG image encoder with Lua API (#11485)

* Add a simple PNG image encoder with Lua API
Add ColorSpec to RGBA converter
Make a safety wrapper for the encoder
Create devtest examples

Co-authored-by: hecktest <>
Co-authored-by: sfan5 <sfan5@live.de>

src/script/lua_api/l_util.cpp

@@ -40,6 +40,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "version.h"
 #include "util/hex.h"
 #include "util/sha1.h"
+#include "util/png.h"
 #include <algorithm>
 #include <cstdio>
 
@@ -497,6 +498,43 @@ int ModApiUtil::l_colorspec_to_colorstring(lua_State *L)
 	return 0;
 }
 
+// colorspec_to_bytes(colorspec)
+int ModApiUtil::l_colorspec_to_bytes(lua_State *L)
+{
+	NO_MAP_LOCK_REQUIRED;
+
+	video::SColor color(0);
+	if (read_color(L, 1, &color)) {
+		u8 colorbytes[4] = {
+			(u8) color.getRed(),
+			(u8) color.getGreen(),
+			(u8) color.getBlue(),
+			(u8) color.getAlpha(),
+		};
+		lua_pushlstring(L, (const char*) colorbytes, 4);
+		return 1;
+	}
+
+	return 0;
+}
+
+// encode_png(w, h, data, level)
+int ModApiUtil::l_encode_png(lua_State *L)
+{
+	NO_MAP_LOCK_REQUIRED;
+
+	// The args are already pre-validated on the lua side.
+	u32 width = readParam<int>(L, 1);
+	u32 height = readParam<int>(L, 2);
+	const char *data = luaL_checklstring(L, 3, NULL);
+	s32 compression = readParam<int>(L, 4);
+
+	std::string out = encodePNG((const u8*)data, width, height, compression);
+
+	lua_pushlstring(L, out.data(), out.size());
+	return 1;
+}
+
 void ModApiUtil::Initialize(lua_State *L, int top)
 {
 	API_FCT(log);
@@ -532,6 +570,9 @@ void ModApiUtil::Initialize(lua_State *L, int top)
 	API_FCT(get_version);
 	API_FCT(sha1);
 	API_FCT(colorspec_to_colorstring);
+	API_FCT(colorspec_to_bytes);
+
+	API_FCT(encode_png);
 
 	LuaSettings::create(L, g_settings, g_settings_path);
 	lua_setfield(L, top, "settings");
@@ -557,6 +598,7 @@ void ModApiUtil::InitializeClient(lua_State *L, int top)
 	API_FCT(get_version);
 	API_FCT(sha1);
 	API_FCT(colorspec_to_colorstring);
+	API_FCT(colorspec_to_bytes);
 }
 
 void ModApiUtil::InitializeAsync(lua_State *L, int top)
@@ -585,6 +627,7 @@ void ModApiUtil::InitializeAsync(lua_State *L, int top)
 	API_FCT(get_version);
 	API_FCT(sha1);
 	API_FCT(colorspec_to_colorstring);
+	API_FCT(colorspec_to_bytes);
 
 	LuaSettings::create(L, g_settings, g_settings_path);
 	lua_setfield(L, top, "settings");

src/script/lua_api/l_util.h

@@ -104,6 +104,12 @@ private:
 	// colorspec_to_colorstring(colorspec)
 	static int l_colorspec_to_colorstring(lua_State *L);
 
+	// colorspec_to_bytes(colorspec)
+	static int l_colorspec_to_bytes(lua_State *L);
+
+	// encode_png(w, h, data, level)
+	static int l_encode_png(lua_State *L);
+
 public:
 	static void Initialize(lua_State *L, int top);
 	static void InitializeAsync(lua_State *L, int top);

src/util/CMakeLists.txt

@@ -15,4 +15,5 @@ set(UTIL_SRCS
 	${CMAKE_CURRENT_SOURCE_DIR}/string.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/srp.cpp
 	${CMAKE_CURRENT_SOURCE_DIR}/timetaker.cpp
+	${CMAKE_CURRENT_SOURCE_DIR}/png.cpp
 	PARENT_SCOPE)

src/util/png.cpp

@@ -0,0 +1,68 @@
+/*
+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)
+{
+	auto file = std::ostringstream(std::ios::binary);
+	file << "\x89PNG\r\n\x1a\n";
+
+	{
+		auto IHDR = std::ostringstream(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());
+	}
+
+	{
+		auto IDAT = std::ostringstream(std::ios::binary);
+		IDAT << "IDAT";
+		auto scanlines = std::ostringstream(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();
+}

src/util/png.h

@@ -0,0 +1,27 @@
+/*
+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.
+*/
+
+#pragma once
+
+#include <string>
+#include "irrlichttypes.h"
+
+/*	Simple PNG encoder. Encodes an RGBA image with no predictors.
+	Returns a binary string. */
+std::string encodePNG(const u8 *data, u32 width, u32 height, s32 compression);