image_modifications.cpp

Go to the documentation of this file.

/*
    Copyright (C) 2009 - 2025
    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 <utility>
 
#include "color.hpp"
#include "config.hpp"
#include "game_config.hpp"
#include "picture.hpp"
#include "log.hpp"
#include "serialization/string_utils.hpp"
#include "team.hpp"
#include "utils/charconv.hpp"
 
#include "formula/formula.hpp"
#include "formula/callable_objects.hpp"
 
#define GETTEXT_DOMAIN "wesnoth-lib"
 
static lg::log_domain log_display("display");
#define ERR_DP LOG_STREAM(err, log_display)
 
namespace image {
 
void modification_queue::push(std::unique_ptr<modification>&& mod)
{
    priorities_[mod->priority()].push_back(std::move(mod));
}
 
void modification_queue::pop()
{
    auto top_pair = priorities_.begin();
    auto& mod_list = top_pair->second;
 
    // Erase the top element.
    mod_list.erase(mod_list.begin());
 
    // We need to keep the map clean.
    if(mod_list.empty()) {
        priorities_.erase(top_pair);
    }
}
 
std::size_t modification_queue::size() const
{
    std::size_t count = 0;
    for(const auto& [priority, mods] : priorities_) {
        count += mods.size();
    }
 
    return count;
}
 
const modification& modification_queue::top() const
{
    return *priorities_.begin()->second.front();
}
 
 
namespace {
 
/** A function used to parse modification arguments */
using mod_parser = std::function<std::unique_ptr<modification>(std::string_view)>;
 
/** 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, std::less<>> 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
 */
std::unique_ptr<modification> decode_modification(const std::string& encoded_mod)
{
    const std::vector<std::string> split = utils::parenthetical_split(encoded_mod);
 
    if(split.size() != 2) {
        ERR_DP << "error parsing image modifications: " << encoded_mod;
        return nullptr;
    }
 
    const std::string& mod_type = split[0];
    const std::string& args = split[1];
 
    if(const auto parser = mod_parsers.find(mod_type); parser != mod_parsers.end()) {
        return std::invoke(parser->second, args);
    } else {
        ERR_DP << "unknown image function in path: " << mod_type;
        return nullptr;
    }
}
 
} // end anon namespace
 
 
modification::imod_exception::imod_exception(const std::stringstream& message_stream)
    : message(message_stream.str())
{
    this->store();
}
 
modification::imod_exception::imod_exception(const std::string& message)
    : message(message)
{
    this->store();
}
 
/** 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, '~')) {
        if(auto mod = decode_modification(encoded_mod)) {
            mods.push(std::move(mod));
        }
    }
 
    return mods;
}
 
void rc_modification::operator()(surface& src) const
{
    recolor_image(src, rc_map_);
}
 
void fl_modification::operator()(surface& src) const
{
    if(horiz_  && vert_ ) {
        // Slightly faster than doing both a flip and a flop.
        src = rotate_180_surface(src);
    } else if(horiz_) {
        flip_surface(src);
    } else if(vert_) {
        flop_surface(src);
    }
}
 
void rotate_modification::operator()(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;
        case 90:
            src = rotate_90_surface(src, true);
            return;
        case 180:
            src = rotate_180_surface(src);
            return;
        case 270:
            src = rotate_90_surface(src, false);
            return;
        case 360:
            return;
    }
 
    src = rotate_any_surface(src, normalized, zoom_, offset_);
}
 
void gs_modification::operator()(surface& src) const
{
    greyscale_image(src);
}
 
void crop_transparency_modification::operator()(surface& src) const
{
    rect src_rect = get_non_transparent_portion(src);
    if(src_rect.w == src->w && src_rect.h == src->h) {
        return;
    }
 
    if(surface cropped = get_surface_portion(src, src_rect)) {
        src = cropped;
    } else {
        ERR_DP << "Failed to either crop or scale the surface";
    }
}
 
void bw_modification::operator()(surface& src) const
{
    monochrome_image(src, threshold_);
}
 
void sepia_modification::operator()(surface& src) const
{
    sepia_image(src);
}
 
void negative_modification::operator()(surface& src) const
{
    negative_image(src, red_, green_, blue_);
}
 
void plot_alpha_modification::operator()(surface& src) const
{
    alpha_to_greyscale(src);
}
 
void wipe_alpha_modification::operator()(surface& src) const
{
    wipe_alpha(src);
}
 
// TODO: Is this useful enough to move into formula/callable_objects?
class pixel_callable : public wfl::color_callable
{
public:
    pixel_callable(std::size_t index, color_t clr, int w, int h)
        : color_callable(clr), coord(), w(w), h(h)
    {
        coord.x = index % w;
        coord.y = index / w;
    }
 
    void get_inputs(wfl::formula_input_vector& inputs) const override
    {
        color_callable::get_inputs(inputs);
        add_input(inputs, "x");
        add_input(inputs, "y");
        add_input(inputs, "u");
        add_input(inputs, "v");
        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(coord.x);
        } else if(key == "y") {
            return variant(coord.y);
        } else if(key == "width") {
            return variant(w);
        } else if(key == "height") {
            return variant(h);
        } else if(key == "u") {
            return variant(coord.x / static_cast<float>(w));
        } else if(key == "v") {
            return variant(coord.y / static_cast<float>(h));
        }
 
        return color_callable::get_value(key);
    }
 
private:
    point coord;
    int w, h;
};
 
void adjust_alpha_modification::operator()(surface& src) const
{
    if(src) {
        wfl::formula new_alpha(formula_);
 
        surface_lock lock(src);
        std::size_t index{0};
 
        for(auto& pixel : lock.pixel_span()) {
            auto color = color_t::from_argb_bytes(pixel);
 
            auto px = pixel_callable{index++, color, src->w, src->h};
            color.a = std::min<unsigned>(new_alpha.evaluate(px).as_int(), 255);
 
            pixel = color.to_argb_bytes();
        }
    }
}
 
void adjust_channels_modification::operator()(surface& src) const
{
    if(src) {
        wfl::formula new_r(formulas_[0]);
        wfl::formula new_g(formulas_[1]);
        wfl::formula new_b(formulas_[2]);
        wfl::formula new_a(formulas_[3]);
 
        surface_lock lock(src);
        std::size_t index{0};
 
        for(auto& pixel : lock.pixel_span()) {
            auto color = color_t::from_argb_bytes(pixel);
 
            auto px = pixel_callable{index++, color, src->w, src->h};
            color.r = std::min<unsigned>(new_r.evaluate(px).as_int(), 255);
            color.g = std::min<unsigned>(new_g.evaluate(px).as_int(), 255);
            color.b = std::min<unsigned>(new_b.evaluate(px).as_int(), 255);
            color.a = std::min<unsigned>(new_a.evaluate(px).as_int(), 255);
 
            pixel = color.to_argb_bytes();
        }
    }
}
 
void crop_modification::operator()(surface& src) const
{
    rect area = slice_;
    if(area.w == 0) {
        area.w = src->w;
    }
 
    if(area.h == 0) {
        area.h = src->h;
    }
 
    src = cut_surface(src, area);
}
 
void blit_modification::operator()(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);
    }
 
    rect r {x_, y_, 0, 0};
    sdl_blit(surf_, nullptr, src, &r);
}
 
void mask_modification::operator()(surface& src) const
{
    if(src->w == mask_->w && src->h == mask_->h && x_ == 0 && y_ == 0) {
        mask_surface(src, mask_);
        return;
    }
 
    rect r {x_, y_, 0, 0};
    surface new_mask(src->w, src->h);
    sdl_blit(mask_, nullptr, new_mask, &r);
    mask_surface(src, new_mask);
}
 
void light_modification::operator()(surface& src) const
{
    if(src == nullptr) { return; }
 
    // light_surface wants a neutral surface having same dimensions
    if(surf_->w != src->w || surf_->h != src->h) {
        light_surface(src, scale_surface(surf_, src->w, src->h));
    } else {
        light_surface(src, surf_);
    }
}
 
void scale_modification::operator()(surface& src) const
{
    point size = target_size_;
 
    if(size.x <= 0) {
        size.x = src->w;
    } else if(flags_ & X_BY_FACTOR) {
        size.x = src->w * (static_cast<double>(size.x) / 100);
    }
 
    if(size.y <= 0) {
        size.y = src->h;
    } else if(flags_ & Y_BY_FACTOR) {
        size.y = src->h * (static_cast<double>(size.y) / 100);
    }
 
    if(flags_ & PRESERVE_ASPECT_RATIO) {
        const auto ratio = std::min(
            static_cast<long double>(size.x) / src->w,
            static_cast<long double>(size.y) / src->h
        );
 
        size = {
            static_cast<int>(src->w * ratio),
            static_cast<int>(src->h * ratio)
        };
    }
 
    if(flags_ & SCALE_SHARP) {
        src = scale_surface_sharp(src, size.x, size.y);
    } else {
        src = scale_surface_legacy(src, size.x, size.y);
    }
}
 
void xbrz_modification::operator()(surface& src) const
{
    if(z_ != 1) {
        src = scale_surface_xbrz(src, z_);
    }
}
 
void pad_modification::operator()(surface& src) const
{
    // Calculate the new dimensions of the padded surface
    const int new_w = src->w + left_ + right_;
    const int new_h = src->h + top_ + bottom_;
 
    // Create a new transparent surface with the calculated dimensions
    surface padded(new_w, new_h);
 
    // Define the destination rectangle for the original image
    rect dstrect{
        left_,
        top_,
        0, // These two values are ignored by SDL_BlitSurface, so we set them to 0.
        0  // The function always blits the entire source surface.
    };
 
    SDL_BlendMode original_blend_mode;
    SDL_GetSurfaceBlendMode(src, &original_blend_mode);
    // Set blend mode to none to prevent blending
    SDL_SetSurfaceBlendMode(src, SDL_BLENDMODE_NONE);
 
    // Blit the original surface onto the new, padded surface
    SDL_BlitSurface(src, nullptr, padded, &dstrect);
 
    SDL_SetSurfaceBlendMode(padded, original_blend_mode);
 
    src = padded;
}
 
/* The Opacity IPF doesn't seem to work with surface-wide alpha and instead needs per-pixel alpha. */
void o_modification::operator()(surface& src) const
{
    if(src) {
        apply_surface_opacity(src, opacity_);
    }
}
 
void cs_modification::operator()(surface& src) const
{
    if((r_ != 0 || g_ != 0 || b_ != 0)) {
        adjust_surface_color(src, r_, g_, b_);
    }
}
 
void blend_modification::operator()(surface& src) const
{
    blend_surface(src, static_cast<double>(a_), color_t(r_, g_, b_));
}
 
void bl_modification::operator()(surface& src) const
{
    blur_alpha_surface(src, depth_);
}
 
void background_modification::operator()(surface& src) const
{
    surface ret = src.clone();
    SDL_FillSurfaceRect(ret, nullptr, SDL_MapSurfaceRGBA(ret, color_.r, color_.g, color_.b, color_.a));
    sdl_blit(src, nullptr, ret, nullptr);
    src = ret;
}
 
void swap_modification::operator()(surface& src) const
{
    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] = std::move(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 std::unique_ptr<modification> parse_##type##_mod(std::string_view);                        \
    static parse_mod_registration parse_##type##_mod_registration_aux(#type, &parse_##type##_mod);    \
    static std::unique_ptr<modification> parse_##type##_mod(std::string_view args_var)                \
 
// Color-range-based recoloring
REGISTER_MOD_PARSER(TC, args)
{
    const auto params = utils::split_view(args,',');
 
    if(params.size() < 2) {
        ERR_DP << "too few arguments passed to the ~TC() function";
 
        return nullptr;
    }
 
    const int side_n = utils::from_chars<int>(params[0]).value_or(-1);
    if(side_n < 1) {
        ERR_DP << "Invalid side (" << params[0] << ") passed to the ~TC() function";
        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";
        ERR_DP << "bailing out from TC";
 
        return nullptr;
    }
 
    try {
        const color_range& new_color = team::get_side_color_range(side_n);
        const std::vector<color_t>& old_color = game_config::tc_info(params[1]);
 
        return std::make_unique<rc_modification>(generate_color_mapping(new_color, old_color));
    } catch(const config::error& e) {
        ERR_DP << "caught config::error while processing TC: " << e.message;
        ERR_DP << "bailing out from TC";
 
        return nullptr;
    }
}
 
// Team-color-based color range selection and recoloring
REGISTER_MOD_PARSER(RC, args)
{
    const auto recolor_params = utils::split_view(args,'>');
 
    if(recolor_params.size() <= 1) {
        return nullptr;
    }
 
    //
    // recolor source palette to color range
    //
    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]);
 
        return std::make_unique<rc_modification>(generate_color_mapping(new_color, old_color));
    } catch (const config::error& e) {
        ERR_DP
            << "caught config::error while processing color-range RC: "
            << e.message;
        ERR_DP << "bailing out from RC";
        return nullptr;
    }
}
 
// Palette switch
REGISTER_MOD_PARSER(PAL, args)
{
    const auto remap_params = utils::split_view(args,'>');
 
    if(remap_params.size() < 2) {
        ERR_DP << "not enough arguments passed to the ~PAL() function: " << args;
 
        return nullptr;
    }
 
    try {
        color_mapping 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(std::size_t i = 0; i < old_palette.size() && i < new_palette.size(); ++i) {
            rc_map[old_palette[i]] = new_palette[i];
        }
 
        return std::make_unique<rc_modification>(std::move(rc_map));
    } catch(const config::error& e) {
        ERR_DP
            << "caught config::error while processing PAL function: "
            << e.message;
        ERR_DP
            << "bailing out from PAL";
 
        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 std::make_unique<fl_modification>(horiz, vert);
}
 
// Rotations
REGISTER_MOD_PARSER(ROTATE, args)
{
    const auto slice_params = utils::split_view(args, ',', utils::STRIP_SPACES);
 
    switch(slice_params.size()) {
        case 0:
            return std::make_unique<rotate_modification>();
        case 1:
            return std::make_unique<rotate_modification>(
                utils::from_chars<int>(slice_params[0]).value_or(0));
        case 2:
            return std::make_unique<rotate_modification>(
                utils::from_chars<int>(slice_params[0]).value_or(0),
                utils::from_chars<int>(slice_params[1]).value_or(0));
        case 3:
            return std::make_unique<rotate_modification>(
                utils::from_chars<int>(slice_params[0]).value_or(0),
                utils::from_chars<int>(slice_params[1]).value_or(0),
                utils::from_chars<int>(slice_params[2]).value_or(0));
    }
    return nullptr;
}
 
// Grayscale
REGISTER_MOD_PARSER(GS, )
{
    return std::make_unique<gs_modification>();
}
 
// crop transparent padding
REGISTER_MOD_PARSER(CROP_TRANSPARENCY, )
{
    return std::make_unique<crop_transparency_modification>();
}
 
// TODO: should this be made a more general util function?
bool in_range(int val, int min, int max)
{
    return min <= val && val <= max;
}
 
// Black and white
REGISTER_MOD_PARSER(BW, args)
{
    const auto params = utils::split_view(args, ',');
 
    if(params.size() != 1) {
        ERR_DP << "~BW() requires  exactly one argument";
        return nullptr;
    }
 
    // TODO: maybe get this directly as uint8_t?
    const auto threshold = utils::from_chars<int>(params[0]);
    if(!threshold) {
        ERR_DP << "unsupported argument in ~BW() function";
        return nullptr;
    }
 
    if(!in_range(*threshold, 0, 255)) {
        ERR_DP << "~BW() argument out of range 0 - 255";
        return nullptr;
    }
 
    return std::make_unique<bw_modification>(*threshold);
}
 
// Sepia
REGISTER_MOD_PARSER(SEPIA, )
{
    return std::make_unique<sepia_modification>();
}
 
// Negative
REGISTER_MOD_PARSER(NEG, args)
{
    const auto params = utils::split_view(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 std::make_unique<negative_modification>(-1, -1, -1);
 
    case 1: {
        const auto threshold = utils::from_chars<int>(params[0]);
 
        if(threshold && in_range(*threshold, -1, 255)) {
            return std::make_unique<negative_modification>(*threshold, *threshold, *threshold);
        } else {
            ERR_DP << "unsupported argument value in ~NEG() function";
            return nullptr;
        }
    }
 
    case 3: {
        const auto thR = utils::from_chars<int>(params[0]);
        const auto thG = utils::from_chars<int>(params[1]);
        const auto thB = utils::from_chars<int>(params[2]);
 
        if(thR && thG && thB && in_range(*thR, -1, 255) && in_range(*thG, -1, 255) && in_range(*thB, -1, 255)) {
            return std::make_unique<negative_modification>(*thR, *thG, *thB);
        } else {
            ERR_DP << "unsupported argument value in ~NEG() function";
            return nullptr;
        }
    }
 
    default:
        ERR_DP << "~NEG() requires 0, 1 or 3 arguments";
        return nullptr;
    }
}
 
// Plot Alpha
REGISTER_MOD_PARSER(PLOT_ALPHA, )
{
    return std::make_unique<plot_alpha_modification>();
}
 
// Wipe Alpha
REGISTER_MOD_PARSER(WIPE_ALPHA, )
{
    return std::make_unique<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";
        return nullptr;
    }
 
    return std::make_unique<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";
        return nullptr;
    }
 
    return std::make_unique<adjust_channels_modification>(params);
}
 
// Color-shift
REGISTER_MOD_PARSER(CS, args)
{
    const auto factors = utils::split_view(args, ',');
    const std::size_t s = factors.size();
 
    if(s == 0) {
        ERR_DP << "no arguments passed to the ~CS() function";
        return nullptr;
    }
 
    int r = 0, g = 0, b = 0;
 
    r = utils::from_chars<int>(factors[0]).value_or(0);
 
    if(s > 1 ) {
        g = utils::from_chars<int>(factors[1]).value_or(0);
    }
    if(s > 2 ) {
        b = utils::from_chars<int>(factors[2]).value_or(0);
    }
 
    return std::make_unique<cs_modification>(r, g , b);
}
 
// Color blending
REGISTER_MOD_PARSER(BLEND, args)
{
    const auto params = utils::split_view(args, ',');
 
    if(params.size() != 4) {
        ERR_DP << "~BLEND() requires exactly 4 arguments";
        return nullptr;
    }
 
    float opacity = 0.0f;
    const std::string_view& opacity_str = params[3];
    const std::string_view::size_type p100_pos = opacity_str.find('%');
 
    if(p100_pos == std::string::npos)
        opacity = utils::from_chars<float>(opacity_str).value_or(0.0f);
    else {
        // make multiplier
        const std::string_view parsed_field = opacity_str.substr(0, p100_pos);
        opacity = utils::from_chars<float>(parsed_field).value_or(0.0f);
        opacity /= 100.0f;
    }
 
    return std::make_unique<blend_modification>(
        utils::from_chars<int>(params[0]).value_or(0),
        utils::from_chars<int>(params[1]).value_or(0),
        utils::from_chars<int>(params[2]).value_or(0),
        opacity);
}
 
// Crop/slice
REGISTER_MOD_PARSER(CROP, args)
{
    const auto slice_params = utils::split_view(args, ',', utils::STRIP_SPACES);
    const std::size_t s = slice_params.size();
 
    if(s == 0 || (s == 1 && slice_params[0].empty())) {
        ERR_DP << "no arguments passed to the ~CROP() function";
        return nullptr;
    }
 
    rect slice_rect { 0, 0, 0, 0 };
 
    slice_rect.x = utils::from_chars<int16_t>(slice_params[0]).value_or(0);
 
    if(s > 1) {
        slice_rect.y = utils::from_chars<int16_t>(slice_params[1]).value_or(0);
    }
    if(s > 2) {
        slice_rect.w = utils::from_chars<uint16_t>(slice_params[2]).value_or(0);
    }
    if(s > 3) {
        slice_rect.h = utils::from_chars<uint16_t>(slice_params[3]).value_or(0);
    }
 
    return std::make_unique<crop_modification>(slice_rect);
}
 
static bool check_image(const image::locator& img, std::stringstream & message)
{
    if(image::exists(img)) 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 std::size_t s = param.size();
 
    if(s == 0 || (s == 1 && param[0].empty())){
        ERR_DP << "no arguments passed to the ~BLIT() function";
        return nullptr;
    }
 
    if(s > 3){
        ERR_DP << "too many arguments passed to the ~BLIT() function";
        return nullptr;
    }
 
    int x = 0, y = 0;
 
    if(s == 3) {
        x = utils::from_chars<int>(param[1]).value_or(0);
        y = utils::from_chars<int>(param[2]).value_or(0);
    }
 
    const image::locator img(param[0]);
    std::stringstream message;
    message << "~BLIT():";
    if(!check_image(img, message))
        return nullptr;
    surface surf = get_surface(img);
 
    return std::make_unique<blit_modification>(surf, x, y);
}
 
// Mask
REGISTER_MOD_PARSER(MASK, args)
{
    std::vector<std::string> param = utils::parenthetical_split(args, ',');
    const std::size_t s = param.size();
 
    if(s == 0 || (s == 1 && param[0].empty())){
        ERR_DP << "no arguments passed to the ~MASK() function";
        return nullptr;
    }
 
    int x = 0, y = 0;
 
    if(s == 3) {
        x = utils::from_chars<int>(param[1]).value_or(0);
        y = utils::from_chars<int>(param[2]).value_or(0);
    }
 
    if(x < 0 || y < 0) {
        ERR_DP << "negative position arguments in ~MASK() function";
        return nullptr;
    }
 
    const image::locator img(param[0]);
    std::stringstream message;
    message << "~MASK():";
    if(!check_image(img, message))
        return nullptr;
    surface surf = get_surface(img);
 
    return std::make_unique<mask_modification>(surf, x, y);
}
 
// Light
REGISTER_MOD_PARSER(L, args)
{
    if(args.empty()){
        ERR_DP << "no arguments passed to the ~L() function";
        return nullptr;
    }
 
    surface surf = get_surface(std::string{args}); // FIXME: string_view for image::locator::value
    return std::make_unique<light_modification>(surf);
}
 
namespace
{
std::pair<int, bool> parse_scale_value(std::string_view arg)
{
    if(const std::size_t pos = arg.rfind('%'); pos != std::string_view::npos) {
        return { utils::from_chars<int>(arg.substr(0, pos)).value_or(0), true };
    } else {
        return { utils::from_chars<int>(arg).value_or(0), false };
    }
}
 
/** Common helper function to parse scaling IPF inputs. */
utils::optional<std::pair<point, uint8_t>> parse_scale_args(std::string_view args)
{
    const auto scale_params = utils::split_view(args, ',', utils::STRIP_SPACES);
    const std::size_t num_args = scale_params.size();
 
    if(num_args == 0 || (num_args == 1 && scale_params[0].empty())) {
        return utils::nullopt;
    }
 
    uint8_t flags = 0;
    std::array<int, 2> parsed_sizes{0,0};
 
    for(unsigned i = 0; i < std::min<unsigned>(2, num_args); ++i) {
        const auto& [size, relative] = parse_scale_value(scale_params[i]);
 
        if(size < 0) {
            ERR_DP << "Negative size passed to scaling IPF. Original image dimension will be used instead";
            continue;
        }
 
        parsed_sizes[i] = size;
 
        if(relative) {
            flags |= (i == 0 ? scale_modification::X_BY_FACTOR : scale_modification::Y_BY_FACTOR);
        }
    }
 
    return std::pair{point{parsed_sizes[0], parsed_sizes[1]}, flags};
}
 
} // namespace
 
// Scale
REGISTER_MOD_PARSER(SCALE, args)
{
    if(auto params = parse_scale_args(args)) {
        constexpr uint8_t mode = scale_modification::SCALE_LINEAR | scale_modification::FIT_TO_SIZE;
        return std::make_unique<scale_modification>(params->first, mode | params->second);
    } else {
        ERR_DP << "no arguments passed to the ~SCALE() function";
        return nullptr;
    }
}
 
REGISTER_MOD_PARSER(SCALE_SHARP, args)
{
    if(auto params = parse_scale_args(args)) {
        constexpr uint8_t mode = scale_modification::SCALE_SHARP | scale_modification::FIT_TO_SIZE;
        return std::make_unique<scale_modification>(params->first, mode | params->second);
    } else {
        ERR_DP << "no arguments passed to the ~SCALE_SHARP() function";
        return nullptr;
    }
}
 
REGISTER_MOD_PARSER(SCALE_INTO, args)
{
    if(auto params = parse_scale_args(args)) {
        constexpr uint8_t mode = scale_modification::SCALE_LINEAR | scale_modification::PRESERVE_ASPECT_RATIO;
        return std::make_unique<scale_modification>(params->first, mode | params->second);
    } else {
        ERR_DP << "no arguments passed to the ~SCALE_INTO() function";
        return nullptr;
    }
}
 
REGISTER_MOD_PARSER(SCALE_INTO_SHARP, args)
{
    if(auto params = parse_scale_args(args)) {
        constexpr uint8_t mode = scale_modification::SCALE_SHARP | scale_modification::PRESERVE_ASPECT_RATIO;
        return std::make_unique<scale_modification>(params->first, mode | params->second);
    } else {
        ERR_DP << "no arguments passed to the ~SCALE_INTO_SHARP() function";
        return nullptr;
    }
}
 
// xBRZ
REGISTER_MOD_PARSER(XBRZ, args)
{
    const int factor = std::clamp(utils::from_chars<int>(args).value_or(1), 1, 6);
    return std::make_unique<xbrz_modification>(factor);
}
 
// Pad
REGISTER_MOD_PARSER(PAD, args)
{
    int top = 0;
    int right = 0;
    int bottom = 0;
    int left = 0;
 
    // Check for the presence of an '=' sign to determine the parsing mode.
    if(args.find('=') != std::string_view::npos) {
        // --- Keyword-Argument Mode ---
        const auto params = utils::map_split(std::string{args}, ',', '='); // map_split needs a std::string
 
        // Map valid input strings to the corresponding integer reference
        const std::map<std::string, int*> alias_map = {
            {"top", &top},
            {"t", &top},
            {"right", &right},
            {"r", &right},
            {"bottom", &bottom},
            {"b", &bottom},
            {"left", &left},
            {"l", &left},
        };
 
        // Parse and assign values if keywords are valid
        for(const auto& [key, value] : params) {
            auto it = alias_map.find(key);
            if(it != alias_map.end()) {
                if(utils::optional padding = utils::from_chars<int>(value)) {
                    *it->second = padding.value();
                } else {
                    ERR_DP << "~PAD() keyword argument '" << key << "' requires a valid integer value. Received: '" << value << "'.";
                    return nullptr;
                }
            } else {
                ERR_DP << "~PAD() found an unknown keyword: '" << key << "'. Valid keywords: top, t, right, r, bottom, b, left, l.";
                return nullptr;
            }
        }
    } else {
        // --- Numeric-Argument Mode ---
        const auto params = utils::split_view(args, ',');
        if(params.size() != 1) {
            ERR_DP << "~PAD() takes either 1 numeric argument for the padding on all sides or a comma separated list of '<keyword>=<number>' pairs with available keywords: top, t, right, r, bottom, b, left, l.";
            return nullptr;
        }
 
        // Single integer argument: apply to all sides
        if(utils::optional padding = utils::from_chars<int>(params[0])) {
            top = right = bottom = left = padding.value();
        } else {
            ERR_DP << "~PAD() numeric argument (pad all sides) requires a single valid integer. Received: '" << params[0] << "'.";
            return nullptr;
        }
    }
 
    return std::make_unique<pad_modification>(top, right, bottom, left);
}
 
// Gaussian-like blur
REGISTER_MOD_PARSER(BL, args)
{
    const int depth = std::max<int>(0, utils::from_chars<int>(args).value_or(0));
    return std::make_unique<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 = utils::from_chars<float>(args).value_or(0.0f);
    } else {
        // make multiplier
        const std::string_view parsed_field = args.substr(0, p100_pos);
        num = utils::from_chars<float>(parsed_field).value_or(0.0f);
        num /= 100.0f;
    }
 
    return std::make_unique<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 = utils::from_chars<int>(args).value_or(0);
    return std::make_unique<cs_modification>(r, 0, 0);
}
 
// Green component color-shift
REGISTER_MOD_PARSER(G, args)
{
    const int g = utils::from_chars<int>(args).value_or(0);
    return std::make_unique<cs_modification>(0, g, 0);
}
 
// Blue component color-shift
REGISTER_MOD_PARSER(B, args)
{
    const int b = utils::from_chars<int>(args).value_or(0);
    return std::make_unique<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 };
    const auto factors = utils::split_view(args, ',');
 
    for(int i = 0; i < std::min<int>(factors.size(), 4); ++i) {
        c[i] = utils::from_chars<int>(factors[i]).value_or(0);
    }
 
    return std::make_unique<background_modification>(color_t(c[0], c[1], c[2], c[3]));
}
 
// Channel swap
REGISTER_MOD_PARSER(SWAP, args)
{
    const auto params = utils::split_view(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";
        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];
        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];
        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];
        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];
            return nullptr;
        }
    }
 
    return std::make_unique<swap_modification>(redValue, greenValue, blueValue, alphaValue);
}
 
} // end anon namespace
 
} /* end namespace image */