image_modifications.cpp

/*
   Copyright (C) 2009 - 2018 by Iris Morelle <shadowm2006@gmail.com>
   Part of the Battle for Wesnoth Project https://www.wesnoth.org/

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 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.

   See the COPYING file for more details.
*/

#include "image_modifications.hpp"

#include "color.hpp"
#include "config.hpp"
#include "game_config.hpp"
#include "picture.hpp"
#include "lexical_cast.hpp"
#include "log.hpp"
#include "serialization/string_utils.hpp"

#include "formula/formula.hpp"
#include "formula/callable.hpp"

#define GETTEXT_DOMAIN "wesnoth-lib"

static lg::log_domain log_display("display");
#define ERR_DP LOG_STREAM(err, log_display)

namespace image {

/** Adds @a mod to the queue (unless mod is nullptr). */
void modification_queue::push(modification * mod)
{
	// Null pointers do not get stored. (Shouldn't happen, but just in case.)
	if(mod != nullptr) {
		priorities_[mod->priority()].emplace_back(mod);
	}
}

/** Removes the top element from the queue */
void modification_queue::pop()
{
	map_type::iterator top_pair = priorities_.begin();
	auto& top_vector = top_pair->second;

	// Erase the top element.
	top_vector.erase(top_vector.begin());
	if(top_vector.empty()) {
		// We need to keep the map clean.
		priorities_.erase(top_pair);
	}
}

/** Returns the number of elements in the queue. */
size_t modification_queue::size() const
{
	size_t count = 0;
	for(const map_type::value_type& pair : priorities_) {
		count += pair.second.size();
	}

	return count;
}

/** Returns the top element in the queue . */
modification * modification_queue::top() const
{
	return priorities_.begin()->second.front().get();
}


namespace {

/// A function used to parse modification arguments
using mod_parser = std::function<modification*(const std::string&)>;

/** A map of all registered mod parsers
 *
 * The mapping is between the modification name and the parser function pointer
 * An example of an entry would be "TC" -> &parse_TC_mod
 */
std::map<std::string, mod_parser> mod_parsers;

/** Decodes a single modification using an appropriate mod_parser
 *
 * @param encoded_mod A string representing a single modification
 *
 * @return A pointer to the decoded modification object
 * @retval nullptr if the string is invalid or a parser isn't found
 */
modification* decode_modification(const std::string& encoded_mod)
{
	std::vector<std::string> split = utils::parenthetical_split(encoded_mod);

	if(split.size() != 2) {
		ERR_DP << "error parsing image modifications: " << encoded_mod << "\n";
		return nullptr;
	}

	std::string mod_type = split[0];
	std::string args = split[1];

	if(mod_parsers.find(mod_type) == mod_parsers.end()) {
		ERR_DP << "unknown image function in path: " << mod_type << '\n';
		return nullptr;
	}

	return mod_parsers[mod_type](args);
}

} // end anon namespace


modification::imod_exception::imod_exception(const std::stringstream& message_stream)
	: message(message_stream.str())
{
}

modification::imod_exception::imod_exception(const std::string& message)
	: message(message)
{
}

/** Decodes the modification string
 *
 * Important:
 * It creates new objects which need to be deleted after use
 *
 * @param encoded_mods A string representing any number of modifications
 *
 * @return A modification_queue filled with decoded modification pointers
 */
modification_queue modification::decode(const std::string& encoded_mods)
{
	modification_queue mods;

	for(const std::string& encoded_mod : utils::parenthetical_split(encoded_mods, '~')) {
		modification* mod = decode_modification(encoded_mod);

		if(mod) {
			mods.push(mod);
		}
	}

	return mods;
}

surface rc_modification::operator()(const surface& src) const
{
	// unchecked
	return recolor_image(src, rc_map_);
}

surface fl_modification::operator()(const surface& src) const
{
	surface ret = src;

	if(horiz_  && vert_ ) {
		// Slightly faster than doing both a flip and a flop.
		ret = rotate_180_surface(ret);
	} else if(horiz_) {
		ret = flip_surface(ret);
	} else if(vert_) {
		ret = flop_surface(ret);
	}

	return ret;
}

surface rotate_modification::operator()(const surface& src) const
{
	// Convert the number of degrees to the interval [0,360].
	const int normalized = degrees_ >= 0 ?
		degrees_ - 360 * (degrees_ / 360) :
		degrees_ + 360 * (1 + (-degrees_) / 360); // In case compilers disagree as to what -90/360 is.

	switch ( normalized )
	{
		case 0:   return src;
		case 90:  return rotate_90_surface(src, true);
		case 180: return rotate_180_surface(src);
		case 270: return rotate_90_surface(src, false);
		case 360: return src;
	}

	return rotate_any_surface(src, normalized, zoom_, offset_);
}

surface gs_modification::operator()(const surface& src) const
{
	return greyscale_image(src);
}

surface bw_modification::operator()(const surface& src) const
{
	return monochrome_image(src, threshold_);
}

surface sepia_modification::operator()(const surface &src) const
{
	return sepia_image(src);
}

surface negative_modification::operator()(const surface &src) const
{
	return negative_image(src, red_, green_, blue_);
}

surface plot_alpha_modification::operator()(const surface& src) const
{
	return alpha_to_greyscale(src);
}

surface wipe_alpha_modification::operator()(const surface& src) const
{
	return wipe_alpha(src);
}

// TODO: Is this useful enough to move into formula/callable_objects?
class pixel_callable : public wfl::formula_callable
{
public:
	pixel_callable(SDL_Point p, color_t clr, uint32_t w, uint32_t h)
		: p(p), clr(clr), w(w), h(h)
	{}

	void get_inputs(wfl::formula_input_vector& inputs) const override
	{
		add_input(inputs, "x");
		add_input(inputs, "y");
		add_input(inputs, "red");
		add_input(inputs, "green");
		add_input(inputs, "blue");
		add_input(inputs, "alpha");
		add_input(inputs, "height");
		add_input(inputs, "width");
	}

	wfl::variant get_value(const std::string& key) const override
	{
		using wfl::variant;
		if(key == "x") {
			return variant(p.x);
		} else if(key == "y") {
			return variant(p.y);
		} else if(key == "red") {
			return variant(clr.r);
		} else if(key == "green") {
			return variant(clr.g);
		} else if(key == "blue") {
			return variant(clr.b);
		} else if(key == "alpha") {
			return variant(clr.a);
		} else if(key == "width") {
			return variant(w);
		} else if(key == "height") {
			return variant(h);
		}

		return variant();
	}

private:
	SDL_Point p;
	color_t clr;
	uint32_t w, h;
};

surface adjust_alpha_modification::operator()(const surface & src) const
{
	if(src == nullptr) {
		return nullptr;
	}

	wfl::formula new_alpha(formula_);

	surface nsurf(make_neutral_surface(src));

	if(nsurf == nullptr) {
		std::cerr << "could not make neutral surface...\n";
		return nullptr;
	}

	{
		surface_lock lock(nsurf);
		uint32_t* cur = lock.pixels();
		uint32_t* const end = cur + nsurf->w * src->h;
		uint32_t* const beg = cur;

		while(cur != end) {
			color_t pixel;
			pixel.a = (*cur) >> 24;
			pixel.r = (*cur) >> 16;
			pixel.g = (*cur) >> 8;
			pixel.b = (*cur);

			int i = cur - beg;
			SDL_Point p;
			p.y = i / nsurf->w;
			p.x = i % nsurf->w;

			pixel_callable px(p, pixel, nsurf->w, nsurf->h);
			pixel.a = std::min<unsigned>(new_alpha.evaluate(px).as_int(), 255);
			*cur = (pixel.a << 24) + (pixel.r << 16) + (pixel.g << 8) + pixel.b;

			++cur;
		}
	}

	return nsurf;
}

surface adjust_channels_modification::operator()(const surface & src) const
{
	if(src == nullptr) {
		return nullptr;
	}

	wfl::formula new_red(formulas_[0]);
	wfl::formula new_green(formulas_[1]);
	wfl::formula new_blue(formulas_[2]);
	wfl::formula new_alpha(formulas_[3]);

	surface nsurf(make_neutral_surface(src));

	if(nsurf == nullptr) {
		std::cerr << "could not make neutral surface...\n";
		return nullptr;
	}

	{
		surface_lock lock(nsurf);
		uint32_t* cur = lock.pixels();
		uint32_t* const end = cur + nsurf->w * src->h;
		uint32_t* const beg = cur;

		while(cur != end) {
			color_t pixel;
			pixel.a = (*cur) >> 24;
			pixel.r = (*cur) >> 16;
			pixel.g = (*cur) >> 8;
			pixel.b = (*cur);

			int i = cur - beg;
			SDL_Point p;
			p.y = i / nsurf->w;
			p.x = i % nsurf->w;

			pixel_callable px(p, pixel, nsurf->w, nsurf->h);
			pixel.r = std::min<unsigned>(new_red.evaluate(px).as_int(), 255);
			pixel.g = std::min<unsigned>(new_green.evaluate(px).as_int(), 255);
			pixel.b = std::min<unsigned>(new_blue.evaluate(px).as_int(), 255);
			pixel.a = std::min<unsigned>(new_alpha.evaluate(px).as_int(), 255);
			*cur = (pixel.a << 24) + (pixel.r << 16) + (pixel.g << 8) + pixel.b;

			++cur;
		}
	}

	return nsurf;
}

surface crop_modification::operator()(const surface& src) const
{
	SDL_Rect area = slice_;
	if(area.w == 0) {
		area.w = src->w;
	}

	if(area.h == 0) {
		area.h = src->h;
	}

	/*
	 * Unlike other image functions cut_surface does not convert the input
	 * surface to a neutral surface, nor does it convert its return surface
	 * to an optimised surface.
	 *
	 * Since it seems to work for most cases, rather change this caller instead
	 * of the function signature. (The issue was discovered in bug #20876).
	 */
	surface temp = cut_surface(make_neutral_surface(src), area);
	return temp;
}

surface blit_modification::operator()(const surface& src) const
{
	if(x_ >= src->w) {
		std::stringstream sstr;
		sstr << "~BLIT(): x-coordinate '"
			<< x_ << "' larger than destination image's width '"
			<< src->w << "' no blitting performed.\n";

		throw imod_exception(sstr);
	}

	if(y_ >= src->h) {
		std::stringstream sstr;
		sstr << "~BLIT(): y-coordinate '"
			<< y_ << "' larger than destination image's height '"
			<< src->h << "' no blitting performed.\n";

		throw imod_exception(sstr);
	}

	if(surf_->w + x_ < 0) {
		std::stringstream sstr;
		sstr << "~BLIT(): offset and width '"
			<< x_ + surf_->w << "' less than zero no blitting performed.\n";

		throw imod_exception(sstr);
	}

	if(surf_->h + y_ < 0) {
		std::stringstream sstr;
		sstr << "~BLIT(): offset and height '"
			<< y_ + surf_->h << "' less than zero no blitting performed.\n";

		throw imod_exception(sstr);
	}

	surface nsrc = make_neutral_surface(src);
	surface nsurf = make_neutral_surface(surf_);
	SDL_Rect r {x_, y_, 0, 0};
	sdl_blit(nsurf, nullptr, nsrc, &r);
	return nsrc;
}

surface mask_modification::operator()(const surface& src) const
{
	if(src->w == mask_->w &&  src->h == mask_->h && x_ == 0 && y_ == 0) {
		return mask_surface(src, mask_);
	}

	SDL_Rect r {x_, y_, 0, 0};
	surface new_mask = create_neutral_surface(src->w, src->h);
	sdl_blit(mask_, nullptr, new_mask, &r);
	return mask_surface(src, new_mask);
}

surface light_modification::operator()(const surface& src) const {
	if(src == nullptr) { return nullptr; }

	// light_surface wants a neutral surface having same dimensions
	surface nsurf;
	if(surf_->w != src->w || surf_->h != src->h) {
		nsurf = scale_surface(surf_, src->w, src->h);
	} else {
		nsurf = make_neutral_surface(surf_);
	}

	return light_surface(src, nsurf);
}

surface scale_modification::operator()(const surface& src) const
{
	std::pair<int,int> sz = calculate_size(src);

	if(nn_) {
		return scale_surface_sharp(src, sz.first, sz.second);
	} else {
		return scale_surface_legacy(src, sz.first, sz.second);
	}
}

std::pair<int,int> scale_exact_modification::calculate_size(const surface& src) const
{
	const int old_w = src->w;
	const int old_h = src->h;
	int w = get_w();
	int h = get_h();

	if(w <= 0) {
		if(w < 0) {
			ERR_DP << "width of " << fn_ << " is negative - resetting to original width" << std::endl;
		}
		w = old_w;
	}

	if(h <= 0) {
		if(h < 0) {
			ERR_DP << "height of " << fn_ << " is negative - resetting to original height" << std::endl;
		}
		h = old_h;
	}

	return {w, h};
}

std::pair<int,int> scale_into_modification::calculate_size(const surface& src) const
{
	const int old_w = src->w;
	const int old_h = src->h;
	long double w = get_w();
	long double h = get_h();

	if(w <= 0) {
		if(w < 0) {
			ERR_DP << "width of SCALE_INTO is negative - resetting to original width" << std::endl;
		}
		w = old_w;
	}

	if(h <= 0) {
		if(h < 0) {
			ERR_DP << "height of SCALE_INTO is negative - resetting to original height" << std::endl;
		}
		h = old_h;
	}

	long double ratio = std::min(w / old_w, h / old_h);

	return {static_cast<int>(old_w * ratio), static_cast<int>(old_h * ratio)};
}

surface xbrz_modification::operator()(const surface& src) const
{
	if(z_ == 1) {
		return src;
	}

	return scale_surface_xbrz(src, z_);
}

/*
 * The Opacity IPF doesn't seem to work with surface-wide alpha and instead needs per-pixel alpha.
 * If this is needed anywhere else it can be moved back to sdl/utils.*pp.
 */
surface o_modification::operator()(const surface& src) const
{
	surface nsurf(make_neutral_surface(src));

	if(nsurf == nullptr) {
		std::cerr << "could not make neutral surface...\n";
		return nullptr;
	}

	uint16_t amount = ftofxp(opacity_);

	{
		surface_lock lock(nsurf);
		uint32_t* beg = lock.pixels();
		uint32_t* end = beg + nsurf->w * src->h;

		while(beg != end) {
			uint8_t alpha = (*beg) >> 24;

			if(alpha) {
				uint8_t r, g, b;
				r = (*beg) >> 16;
				g = (*beg) >> 8;
				b = (*beg);

				alpha = std::min<unsigned>(unsigned(fxpmult(alpha,amount)), 255);
				*beg = (alpha << 24) + (r << 16) + (g << 8) + b;
			}

			++beg;
		}
	}

	return nsurf;
}

surface cs_modification::operator()(const surface& src) const
{
	return((r_ != 0 || g_ != 0 || b_ != 0)
		? adjust_surface_color(src, r_, g_, b_)
		: src
	);
}

surface blend_modification::operator()(const surface& src) const
{
	return blend_surface(src, static_cast<double>(a_), color_t(r_, g_, b_));
}

surface bl_modification::operator()(const surface& src) const
{
	return blur_alpha_surface(src, depth_);
}

surface background_modification::operator()(const surface &src) const
{
	surface ret = make_neutral_surface(src);
	SDL_FillRect(ret, nullptr, SDL_MapRGBA(ret->format, color_.r, color_.g,
					    color_.b, color_.a));
	surface temp = src;
	sdl_blit(temp, nullptr, ret, nullptr);
	return ret;
}

surface swap_modification::operator()(const surface &src) const
{
	return swap_channels_image(src, red_, green_, blue_, alpha_);
}

namespace {

struct parse_mod_registration
{
	parse_mod_registration(const char* name, mod_parser parser)
	{
		mod_parsers[name] = parser;
	}
};

/** A macro for automatic modification parser registration
 *
 * It automatically registers the created parser in the mod_parsers map
 * It should be used just like a function header (look at the uses below)
 * It should only be used within an anonymous namespace
 *
 * @param type The modification type to be registered (unquoted)
 * @param args_var The name for the string argument provided
 */
#define REGISTER_MOD_PARSER(type, args_var)                                                           \
    static modification* parse_##type##_mod(const std::string&);                                      \
    static parse_mod_registration parse_##type##_mod_registration_aux(#type, &parse_##type##_mod);    \
    static modification* parse_##type##_mod(const std::string& args_var)                              \

// Color-range-based recoloring
REGISTER_MOD_PARSER(TC, args)
{
	std::vector<std::string> params = utils::split(args,',');

	if(params.size() < 2) {
		ERR_DP << "too few arguments passed to the ~TC() function" << std::endl;

		return nullptr;
	}

	int side_n = lexical_cast_default<int>(params[0], -1);
	std::string team_color;
	if(side_n < 1) {
		ERR_DP << "invalid team (" << side_n
		       << ") passed to the ~TC() function\n";
		return nullptr;
	} else if(side_n <= static_cast<int>(image::get_team_colors().size())) {
		team_color = image::get_team_colors()[side_n - 1];
	} else {
		// This side is not initialized; use default "n"
		try {
			team_color = std::to_string(side_n);
		} catch(const bad_lexical_cast&) {
			ERR_DP << "bad things happen" << std::endl;

			return nullptr;
		}
	}

	//
	// Pass argseters for RC functor
	//
	if(!game_config::tc_info(params[1]).size()){
		ERR_DP << "could not load TC info for '" << params[1]
		       << "' palette\n"
		       << "bailing out from TC\n";

		return nullptr;
	}

	color_range_map rc_map;
	try {
		const color_range& new_color = game_config::color_info(team_color);
		const std::vector<color_t>& old_color = game_config::tc_info(params[1]);

		rc_map = recolor_range(new_color,old_color);
	} catch(const config::error& e) {
		ERR_DP << "caught config::error while processing TC: "
		       << e.message
		       << '\n'
		       << "bailing out from TC\n";

		return nullptr;
	}

	return new rc_modification(rc_map);
}

// Team-color-based color range selection and recoloring
REGISTER_MOD_PARSER(RC, args)
{
	const std::vector<std::string> recolor_params = utils::split(args,'>');

	if(recolor_params.size() <= 1) {
		return nullptr;
	}

	//
	// recolor source palette to color range
	//
	color_range_map rc_map;
	try {
		const color_range& new_color = game_config::color_info(recolor_params[1]);
		const std::vector<color_t>& old_color = game_config::tc_info(recolor_params[0]);

		rc_map = recolor_range(new_color,old_color);
	} catch (const config::error& e) {
		ERR_DP
			<< "caught config::error while processing color-range RC: "
			<< e.message
			<< '\n';
		ERR_DP
			<< "bailing out from RC\n";
		rc_map.clear();
	}

	return new rc_modification(rc_map);
}

// Palette switch
REGISTER_MOD_PARSER(PAL, args)
{
	const std::vector<std::string> remap_params = utils::split(args,'>');

	if(remap_params.size() < 2) {
		ERR_DP << "not enough arguments passed to the ~PAL() function: " << args << "\n";

		return nullptr;
	}

	try {
		color_range_map rc_map;
		const std::vector<color_t>& old_palette = game_config::tc_info(remap_params[0]);
		const std::vector<color_t>& new_palette =game_config::tc_info(remap_params[1]);

		for(size_t i = 0; i < old_palette.size() && i < new_palette.size(); ++i) {
			rc_map[old_palette[i]] = new_palette[i];
		}

		return new rc_modification(rc_map);
	} catch(const config::error& e) {
		ERR_DP
			<< "caught config::error while processing PAL function: "
			<< e.message
			<< '\n';
		ERR_DP
			<< "bailing out from PAL\n";

		return nullptr;
	}
}

// Flip/flop
REGISTER_MOD_PARSER(FL, args)
{
	bool horiz = (args.empty() || args.find("horiz") != std::string::npos);
	bool vert = (args.find("vert") != std::string::npos);

	return new fl_modification(horiz, vert);
}

// Rotations
REGISTER_MOD_PARSER(ROTATE, args)
{
	const std::vector<std::string>& slice_params = utils::split(args, ',', utils::STRIP_SPACES);
	const size_t s = slice_params.size();

	switch(s) {
		case 0:
			return new rotate_modification();
			break;
		case 1:
			return new rotate_modification(
				lexical_cast_default<int>(slice_params[0]));
			break;
		case 2:
			return new rotate_modification(
				lexical_cast_default<int>(slice_params[0]),
				lexical_cast_default<int>(slice_params[1]));
			break;
		case 3:
			return new rotate_modification(
				lexical_cast_default<int>(slice_params[0]),
				lexical_cast_default<int>(slice_params[1]),
				lexical_cast_default<int>(slice_params[2]));
			break;
	}
	return nullptr;
}

// Grayscale
REGISTER_MOD_PARSER(GS, )
{
	return new gs_modification;
}

// Black and white
REGISTER_MOD_PARSER(BW, args)
{
	const std::vector<std::string>& params = utils::split(args, ',');

	if(params.size() != 1) {
		ERR_DP << "~BW() requires  exactly one argument" << std::endl;
		return nullptr;
	}

	try {
		int threshold = std::stoi(params[0]);
		if(threshold < 0 || threshold > 255) {
			ERR_DP << "~BW() argument out of range 0 - 255" << std::endl;
			return nullptr;
		}  else {
			return new bw_modification(threshold);
		}
	} catch (const std::invalid_argument&) {
		ERR_DP << "unsupported argument in ~BW() function" << std::endl;
		return nullptr;
	}
}

// Sepia
REGISTER_MOD_PARSER(SEPIA, )
{
	return new sepia_modification;
}

// Negative
REGISTER_MOD_PARSER(NEG, args)
{
	const std::vector<std::string>& params = utils::split(args, ',');

	switch (params.size()) {
		case 0:
			// apparently -1 may be a magic number
			// but this is the threshold value required
			// to fully invert a channel
			return new negative_modification(-1,-1,-1);
			break;
		case 1:
			try {
				int threshold = std::stoi(params[0]);
				if(threshold < -1 || threshold > 255) {
					ERR_DP << "unsupported argument value in ~NEG() function" << std::endl;
					return nullptr;
				} else {
					return new negative_modification(threshold, threshold, threshold);
				}
			} catch (const std::invalid_argument&) {
				ERR_DP << "unsupported argument value in ~NEG() function" << std::endl;
				return nullptr;
			}
			break;
		case 3:
			try {
				int thresholdRed = std::stoi(params[0]);
				int thresholdGreen = std::stoi(params[1]);
				int thresholdBlue = std::stoi(params[2]);
				if(thresholdRed < -1 || thresholdRed > 255 || thresholdGreen < -1 || thresholdGreen > 255 || thresholdBlue < -1 || thresholdBlue > 255) {
					ERR_DP << "unsupported argument value in ~NEG() function" << std::endl;
					return nullptr;
				} else {
					return new negative_modification(thresholdRed, thresholdGreen, thresholdBlue);
				}
			} catch (const std::invalid_argument&) {
				ERR_DP << "unsupported argument value in ~NEG() function" << std::endl;
				return nullptr;
			}
			break;
		default:
			ERR_DP << "~NEG() requires 0, 1 or 3 arguments" << std::endl;
			return nullptr;
	}

	return nullptr;
}

// Plot Alpha
REGISTER_MOD_PARSER(PLOT_ALPHA, )
{
	return new plot_alpha_modification;
}

// Wipe Alpha
REGISTER_MOD_PARSER(WIPE_ALPHA, )
{
	return new wipe_alpha_modification;
}

// Adjust Alpha
REGISTER_MOD_PARSER(ADJUST_ALPHA, args)
{
	// Formulas may contain commas, so use parenthetical split to ensure that they're properly considered a single argument.
	// (A comma in a formula is only valid in function parameters or list/map literals, so this should always work.)
	const std::vector<std::string>& params = utils::parenthetical_split(args, ',', "([", ")]");

	if(params.size() != 1) {
		ERR_DP << "~ADJUST_ALPHA() requires exactly 1 arguments" << std::endl;
		return nullptr;
	}

	return new adjust_alpha_modification(params.at(0));
}

// Adjust Channels
REGISTER_MOD_PARSER(CHAN, args)
{
	// Formulas may contain commas, so use parenthetical split to ensure that they're properly considered a single argument.
	// (A comma in a formula is only valid in function parameters or list/map literals, so this should always work.)
	const std::vector<std::string>& params = utils::parenthetical_split(args, ',', "([", ")]");

	if(params.size() < 1 || params.size() > 4) {
		ERR_DP << "~CHAN() requires 1 to 4 arguments" << std::endl;
		return nullptr;
	}

	return new adjust_channels_modification(params);
}

// Color-shift
REGISTER_MOD_PARSER(CS, args)
{
	std::vector<std::string> const factors = utils::split(args, ',');
	const size_t s = factors.size();

	if(s == 0) {
		ERR_DP << "no arguments passed to the ~CS() function" << std::endl;
		return nullptr;
	}

	int r = 0, g = 0, b = 0;

	r = lexical_cast_default<int>(factors[0]);

	if(s > 1 ) {
		g = lexical_cast_default<int>(factors[1]);
	}
	if(s > 2 ) {
		b = lexical_cast_default<int>(factors[2]);
	}

	return new cs_modification(r, g, b);
}

// Color blending
REGISTER_MOD_PARSER(BLEND, args)
{
	const std::vector<std::string>& params = utils::split(args, ',');

	if(params.size() != 4) {
		ERR_DP << "~BLEND() requires exactly 4 arguments" << std::endl;
		return nullptr;
	}

	float opacity = 0.0f;
	const std::string& opacity_str = params[3];
	const std::string::size_type p100_pos = opacity_str.find('%');

	if(p100_pos == std::string::npos)
		opacity = lexical_cast_default<float>(opacity_str);
	else {
		// make multiplier
		const std::string& parsed_field = opacity_str.substr(0, p100_pos);
		opacity = lexical_cast_default<float>(parsed_field);
		opacity /= 100.0f;
	}

	return new blend_modification(
		lexical_cast_default<int>(params[0]),
		lexical_cast_default<int>(params[1]),
		lexical_cast_default<int>(params[2]),
		opacity);
}

// Crop/slice
REGISTER_MOD_PARSER(CROP, args)
{
	const std::vector<std::string>& slice_params = utils::split(args, ',', utils::STRIP_SPACES);
	const size_t s = slice_params.size();

	if(s == 0 || (s == 1 && slice_params[0].empty())) {
		ERR_DP << "no arguments passed to the ~CROP() function" << std::endl;
		return nullptr;
	}

	SDL_Rect slice_rect { 0, 0, 0, 0 };

	slice_rect.x = lexical_cast_default<int16_t, const std::string&>(slice_params[0]);

	if(s > 1) {
		slice_rect.y = lexical_cast_default<int16_t, const std::string&>(slice_params[1]);
	}
	if(s > 2) {
		slice_rect.w = lexical_cast_default<uint16_t, const std::string&>(slice_params[2]);
	}
	if(s > 3) {
		slice_rect.h = lexical_cast_default<uint16_t, const std::string&>(slice_params[3]);
	}

	return new crop_modification(slice_rect);
}

static bool check_image(const image::locator& img, std::stringstream & message)
{
	if(img.file_exists()) return true;
	message << " image not found: '" << img.get_filename() << "'\n";
	ERR_DP << message.str();
	return false;
}

// Blit
REGISTER_MOD_PARSER(BLIT, args)
{
	std::vector<std::string> param = utils::parenthetical_split(args, ',');
	const size_t s = param.size();

	if(s == 0 || (s == 1 && param[0].empty())){
		ERR_DP << "no arguments passed to the ~BLIT() function" << std::endl;
		return nullptr;
	}
	
	if(s > 3){
		ERR_DP << "too many arguments passed to the ~BLIT() function" << std::endl;
		return nullptr;
	}
	
	int x = 0, y = 0;

	if(s == 3) {
		x = lexical_cast_default<int>(param[1]);
		y = lexical_cast_default<int>(param[2]);
	}

	const image::locator img(param[0]);
	std::stringstream message;
	message << "~BLIT():";
	if(!check_image(img, message))
		return nullptr;
	surface surf = get_image(img);

	return new blit_modification(surf, x, y);
}

// Mask
REGISTER_MOD_PARSER(MASK, args)
{
	std::vector<std::string> param = utils::parenthetical_split(args, ',');
	const size_t s = param.size();

	if(s == 0 || (s == 1 && param[0].empty())){
		ERR_DP << "no arguments passed to the ~MASK() function" << std::endl;
		return nullptr;
	}

	int x = 0, y = 0;

	if(s == 3) {
		x = lexical_cast_default<int>(param[1]);
		y = lexical_cast_default<int>(param[2]);
	}

	if(x < 0 || y < 0) {
		ERR_DP << "negative position arguments in ~MASK() function" << std::endl;
		return nullptr;
	}

	const image::locator img(param[0]);
	std::stringstream message;
	message << "~MASK():";
	if(!check_image(img, message))
		return nullptr;
	surface surf = get_image(img);

	return new mask_modification(surf, x, y);
}

// Light
REGISTER_MOD_PARSER(L, args)
{
	if(args.empty()){
		ERR_DP << "no arguments passed to the ~L() function" << std::endl;
		return nullptr;
	}

	surface surf = get_image(args);

	return new light_modification(surf);
}

// Scale
REGISTER_MOD_PARSER(SCALE, args)
{
	const std::vector<std::string>& scale_params = utils::split(args, ',', utils::STRIP_SPACES);
	const size_t s = scale_params.size();

	if(s == 0 || (s == 1 && scale_params[0].empty())) {
		ERR_DP << "no arguments passed to the ~SCALE() function" << std::endl;
		return nullptr;
	}

	int w = 0, h = 0;

	w = lexical_cast_default<int, const std::string&>(scale_params[0]);

	if(s > 1) {
		h = lexical_cast_default<int, const std::string&>(scale_params[1]);
	}

	return new scale_exact_modification(w, h, "SCALE", false);
}

REGISTER_MOD_PARSER(SCALE_SHARP, args)
{
	const std::vector<std::string>& scale_params = utils::split(args, ',', utils::STRIP_SPACES);
	const size_t s = scale_params.size();

	if(s == 0 || (s == 1 && scale_params[0].empty())) {
		ERR_DP << "no arguments passed to the ~SCALE_SHARP() function" << std::endl;
		return nullptr;
	}

	int w = 0, h = 0;

	w = lexical_cast_default<int, const std::string&>(scale_params[0]);

	if(s > 1) {
		h = lexical_cast_default<int, const std::string&>(scale_params[1]);
	}

	return new scale_exact_modification(w, h, "SCALE_SHARP", true);
}

REGISTER_MOD_PARSER(SCALE_INTO, args)
{
	const std::vector<std::string>& scale_params = utils::split(args, ',', utils::STRIP_SPACES);
	const size_t s = scale_params.size();

	if(s == 0 || (s == 1 && scale_params[0].empty())) {
		ERR_DP << "no arguments passed to the ~SCALE_INTO() function" << std::endl;
		return nullptr;
	}

	int w = 0, h = 0;

	w = lexical_cast_default<int, const std::string&>(scale_params[0]);

	if(s > 1) {
		h = lexical_cast_default<int, const std::string&>(scale_params[1]);
	}

	return new scale_into_modification(w, h, "SCALE_INTO", false);
}

REGISTER_MOD_PARSER(SCALE_INTO_SHARP, args)
{
	const std::vector<std::string>& scale_params = utils::split(args, ',', utils::STRIP_SPACES);
	const size_t s = scale_params.size();

	if(s == 0 || (s == 1 && scale_params[0].empty())) {
		ERR_DP << "no arguments passed to the ~SCALE_INTO_SHARP() function" << std::endl;
		return nullptr;
	}

	int w = 0, h = 0;

	w = lexical_cast_default<int, const std::string&>(scale_params[0]);

	if(s > 1) {
		h = lexical_cast_default<int, const std::string&>(scale_params[1]);
	}

	return new scale_into_modification(w, h, "SCALE_INTO_SHARP", true);
}

// xBRZ
REGISTER_MOD_PARSER(XBRZ, args)
{
	int z = lexical_cast_default<int, const std::string &>(args);
	if(z < 1 || z > 5) {
		z = 5; //only values 2 - 5 are permitted for xbrz scaling factors.
	}

	return new xbrz_modification(z);
}

// scale

// Gaussian-like blur
REGISTER_MOD_PARSER(BL, args)
{
	const int depth = std::max<int>(0, lexical_cast_default<int>(args));

	return new bl_modification(depth);
}

// Opacity-shift
REGISTER_MOD_PARSER(O, args)
{
	const std::string::size_type p100_pos = args.find('%');
	float num = 0.0f;
	if(p100_pos == std::string::npos) {
		num = lexical_cast_default<float,const std::string&>(args);
	} else {
		// make multiplier
		const std::string parsed_field = args.substr(0, p100_pos);
		num = lexical_cast_default<float,const std::string&>(parsed_field);
		num /= 100.0f;
	}

	return new o_modification(num);
}

//
// ~R(), ~G() and ~B() are the children of ~CS(). Merely syntactic sugar.
// Hence they are at the end of the evaluation.
//
// Red component color-shift
REGISTER_MOD_PARSER(R, args)
{
	const int r = lexical_cast_default<int>(args);

	return new cs_modification(r,0,0);
}

// Green component color-shift
REGISTER_MOD_PARSER(G, args)
{
	const int g = lexical_cast_default<int>(args);

	return new cs_modification(0,g,0);
}

// Blue component color-shift
REGISTER_MOD_PARSER(B, args)
{
	const int b = lexical_cast_default<int>(args);

	return new cs_modification(0,0,b);
}

REGISTER_MOD_PARSER(NOP, )
{
	return nullptr;
}

// Only used to tag terrain images which should not be color-shifted by ToD
REGISTER_MOD_PARSER(NO_TOD_SHIFT, )
{
	return nullptr;
}

// Fake image function used by GUI2 portraits until
// Mordante gets rid of it. *tsk* *tsk*
REGISTER_MOD_PARSER(RIGHT, )
{
	return nullptr;
}

// Add a background color.
REGISTER_MOD_PARSER(BG, args)
{
	int c[4] { 0, 0, 0, SDL_ALPHA_OPAQUE };
	std::vector<std::string> factors = utils::split(args, ',');

	for(int i = 0; i < std::min<int>(factors.size(), 4); ++i) {
		c[i] = lexical_cast_default<int>(factors[i]);
	}

	return new background_modification(color_t(c[0], c[1], c[2], c[3]));
}

// Channel swap
REGISTER_MOD_PARSER(SWAP, args)
{
	std::vector<std::string> params = utils::split(args, ',', utils::STRIP_SPACES);

	// accept 3 arguments (rgb) or 4 (rgba)
	if(params.size() != 3 && params.size() != 4) {
		ERR_DP << "incorrect number of arguments in ~SWAP() function, they must be 3 or 4" << std::endl;
		return nullptr;
	}

	channel redValue, greenValue, blueValue, alphaValue;
	// compare the parameter's value with the constants defined in the channels enum
	if(params[0] == "red") {
		redValue = RED;
	} else if(params[0] == "green") {
		redValue = GREEN;
	} else if(params[0] == "blue") {
		redValue = BLUE;
	} else if(params[0] == "alpha") {
		redValue = ALPHA;
	} else {
		ERR_DP << "unsupported argument value in ~SWAP() function: " << params[0] << std::endl;
		return nullptr;
	}

	// wash, rinse and repeat for the other three channels
	if(params[1] == "red") {
		greenValue = RED;
	} else if(params[1] == "green") {
		greenValue = GREEN;
	} else if(params[1] == "blue") {
		greenValue = BLUE;
	} else if(params[1] == "alpha") {
		greenValue = ALPHA;
	} else {
		ERR_DP << "unsupported argument value in ~SWAP() function: " << params[0] << std::endl;
		return nullptr;
	}

	if(params[2] == "red") {
		blueValue = RED;
	} else if(params[2] == "green") {
		blueValue = GREEN;
	} else if(params[2] == "blue") {
		blueValue = BLUE;
	} else if(params[2] == "alpha") {
		blueValue = ALPHA;
	} else {
		ERR_DP << "unsupported argument value in ~SWAP() function: " << params[0] << std::endl;
		return nullptr;
	}

	// additional check: the params vector may not have a fourth elementh
	// if so, default to the same channel
	if(params.size() == 3) {
		alphaValue = ALPHA;
	} else {
		if(params[3] == "red") {
			alphaValue = RED;
		} else if(params[3] == "green") {
			alphaValue = GREEN;
		} else if(params[3] == "blue") {
			alphaValue = BLUE;
		} else if(params[3] == "alpha") {
			alphaValue = ALPHA;
		} else {
			ERR_DP << "unsupported argument value in ~SWAP() function: " << params[3] << std::endl;
			return nullptr;
		}
	}

	return new swap_modification(redValue, greenValue, blueValue, alphaValue);
}

} // end anon namespace

} /* end namespace image */