udisplay.cpp

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/*
    Copyright (C) 2003 - 2022
    by David White <dave@whitevine.net>
    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 "units/udisplay.hpp"

#include "fake_unit_manager.hpp"
#include "fake_unit_ptr.hpp"
#include "game_board.hpp"
#include "game_display.hpp"
#include "preferences/game.hpp"
#include "log.hpp"
#include "mouse_events.hpp"
#include "resources.hpp"
#include "color.hpp"
#include "sound.hpp"
#include "terrain/filter.hpp"
#include "units/unit.hpp"
#include "units/animation_component.hpp"
#include "units/filter.hpp"
#include "units/map.hpp"
#include "utils/scope_exit.hpp"
#include "video.hpp"

#define LOG_DP LOG_STREAM(info, display)


namespace unit_display
{
namespace
{
/**
 * Returns a string whose first line is @a number, centered over a second line,
 * which consists of @a text.
 * If the number is 0, the first line is suppressed.
 */
std::string number_and_text(int number, const std::string& text)
{
    // Simple case.
    if ( number == 0 )
        return text;

    std::ostringstream result;

    if ( text.empty() )
        result << number;
    else
        result << std::string((text.size()+1)/2, ' ') << number << '\n' << text;

    return result.str();
}


/**
 * Animates a teleportation between hexes.
 *
 * @param a          The starting hex.
 * @param b          The ending hex.
 * @param temp_unit  The unit to animate (historically, a temporary unit).
 * @param disp       The game display. Assumed neither locked nor faked.
 */
void teleport_unit_between(const map_location& a, const map_location& b, unit& temp_unit, display& disp)
{
    if ( disp.fogged(a) && disp.fogged(b) ) {
        return;
    }
    const display_context& dc = disp.get_disp_context();
    const team& viewing_team = dc.get_team(disp.viewing_side());

    const bool a_visible = temp_unit.is_visible_to_team(a, viewing_team, false);
    const bool b_visible = temp_unit.is_visible_to_team(b, viewing_team, false);

    temp_unit.set_location(a);
    if ( a_visible ) { // teleport
        disp.invalidate(a);
        temp_unit.set_facing(a.get_relative_dir(b));
        if ( b_visible )
            disp.scroll_to_tiles(a, b, game_display::ONSCREEN, true, 0.0, false);
        else
            disp.scroll_to_tile(a, game_display::ONSCREEN, true, false);
        unit_animator animator;
        animator.add_animation(temp_unit.shared_from_this(),"pre_teleport",a);
        animator.start_animations();
        animator.wait_for_end();
    }

    temp_unit.set_location(b);
    if ( b_visible ) { // teleport
        disp.invalidate(b);
        temp_unit.set_facing(a.get_relative_dir(b));
        if ( a_visible )
            disp.scroll_to_tiles(b, a, game_display::ONSCREEN, true, 0.0, false);
        else
            disp.scroll_to_tile(b, game_display::ONSCREEN, true, false);
        unit_animator animator;
        animator.add_animation(temp_unit.shared_from_this(),"post_teleport",b);
        animator.start_animations();
        animator.wait_for_end();
    }

    temp_unit.anim_comp().set_standing();
    events::pump();
}

/**
 * Animates a single step between hexes.
 * This will return before the animation actually finishes, allowing other
 * processing to occur during the animation.
 *
 * @param a          The starting hex.
 * @param b          The ending hex.
 * @param temp_unit  The unit to animate (historically, a temporary unit).
 * @param step_num   The number of steps taken so far (used to pick an animation).
 * @param step_left  The number of steps remaining (used to pick an animation).
 * @param animator   The unit_animator to use. This is assumed clear when we start,
 *                   but will likely not be clear when we return.
 * @param disp       The game display. Assumed neither locked nor faked.
 * @returns  The animation potential until this animation will finish.
 *           INT_MIN indicates that no animation is pending.
 */
int move_unit_between(const map_location& a,
        const map_location& b,
        unit_ptr temp_unit,
        unsigned int step_num,
        unsigned int step_left,
        unit_animator& animator,
        display& disp)
{
    if ( disp.fogged(a) && disp.fogged(b) ) {
        return INT_MIN;
    }

    temp_unit->set_location(a);
    disp.invalidate(a);
    temp_unit->set_facing(a.get_relative_dir(b));
    animator.replace_anim_if_invalid(temp_unit,"movement",a,b,step_num,
            false,"",{0,0,0},strike_result::type::invalid,nullptr,nullptr,step_left);
    animator.start_animations();
    animator.pause_animation();
    disp.scroll_to_tiles(a, b, game_display::ONSCREEN, true, 0.0, false);
    animator.restart_animation();

    // useless now, previous short draw() just did one
    // new_animation_frame();

    int target_time = animator.get_animation_time_potential();
        // target_time must be short to avoid jumpy move
        // std::cout << "target time: " << target_time << "\n";
    // we round it to the next multiple of 200 so that movement aligns to hex changes properly
    target_time += 200;
    target_time -= target_time%200;

    return target_time;
}

bool do_not_show_anims(display* disp)
{

    return !disp || video::headless();
}

} // end anon namespace

/**
 * The path must remain unchanged for the life of this object.
 */
unit_mover::unit_mover(const std::vector<map_location>& path, bool animate, bool force_scroll) :
    disp_(game_display::get_singleton()),
    can_draw_(disp_ && !video::headless() && path.size() > 1),
    animate_(animate),
    force_scroll_(force_scroll),
    animator_(),
    wait_until_(INT_MIN),
    shown_unit_(),
    path_(path),
    current_(0),
    temp_unit_ptr_(),
    // Somewhat arbitrary default values.
    was_hidden_(false),
    is_enemy_(true)
{
    // Some error conditions that indicate something has gone very wrong.
    // (This class can handle these conditions, but someone wanted them
    // to be assertions.)
    assert(!path_.empty());
    assert(disp_);
}


unit_mover::~unit_mover()
{
    // Make sure a unit hidden for movement is unhidden.
    update_shown_unit();
    // For safety, clear the animator before deleting the temp unit.
    animator_.clear();
}


/**
 * Makes the temporary unit used by this match the supplied unit.
 * This is called when setting the initial unit, as well as replacing it with
 * something new.
 * When this finishes, the supplied unit is hidden, while the temporary unit
 * is not hidden.
 */
/* Note: Hide the unit in its current location; do not actually remove it.
 * Otherwise the status displays will be wrong during the movement.
 */
void unit_mover::replace_temporary(unit_ptr u)
{
    if ( disp_ == nullptr )
        // No point in creating a temp unit with no way to display it.
        return;

    // Save the hidden state of the unit.
    was_hidden_ = u->get_hidden();

    // Make our temporary unit mostly match u...
    temp_unit_ptr_ = fake_unit_ptr(u->clone(), resources::fake_units);

    // ... but keep the temporary unhidden and hide the original.
    temp_unit_ptr_->set_hidden(false);
    u->set_hidden(true);

    // Update cached data.
    is_enemy_ = resources::gameboard->get_team(u->side()).is_enemy(disp_->viewing_side());
}


/**
 * Switches the display back to *shown_unit_ after animating.
 * This uses temp_unit_ptr_, so (in the destructor) call this before deleting
 * temp_unit_ptr_.
 */
void unit_mover::update_shown_unit()
{
    if ( shown_unit_ ) {
        // Switch the display back to the real unit.
        shown_unit_->set_hidden(was_hidden_);
        temp_unit_ptr_->set_hidden(true);
        shown_unit_.reset();
    }
}


/**
 * Initiates the display of movement for the supplied unit.
 * This should be called before attempting to display moving to a new hex.
 */
void unit_mover::start(unit_ptr u)
{
    // Nothing to do here if there is nothing to animate.
    if ( !can_draw_ )
        return;
    // If no animation then hide unit until end of movement
    if ( !animate_ ) {
        was_hidden_ = u->get_hidden();
        u->set_hidden(true);
        return;
    }

    // This normally does nothing, but just in case...
    wait_for_anims();

    // Visually replace the original unit with the temporary.
    // (Original unit is left on the map, so the unit count is correct.)
    replace_temporary(u);

    // Initialize our temporary unit for the move.
    temp_unit_ptr_->set_location(path_[0]);
    temp_unit_ptr_->set_facing(path_[0].get_relative_dir(path_[1]));
    temp_unit_ptr_->anim_comp().set_standing(false);
    disp_->invalidate(path_[0]);

    // If the unit can be seen here by the viewing side:
    if(!is_enemy_ || !temp_unit_ptr_->invisible(path_[0])) {
        // Scroll to the path, but only if it fully fits on screen.
        // If it does not fit we might be able to do a better scroll later.
        disp_->scroll_to_tiles(path_, game_display::ONSCREEN, true, true, 0.0, false);
    }

    // extra immobile movement animation for take-off
    animator_.add_animation(temp_unit_ptr_.get_unit_ptr(), "pre_movement", path_[0], path_[1]);
    animator_.start_animations();
    animator_.wait_for_end();
    animator_.clear();

    // Switch the display back to the real unit.
    u->set_facing(temp_unit_ptr_->facing());
    u->anim_comp().set_standing(false); // Need to reset u's animation so the new facing takes effect.
    u->set_hidden(was_hidden_);
    temp_unit_ptr_->set_hidden(true);
}


/**
 * Visually moves a unit from the last hex we drew to the one specified by
 * @a path_index. If @a path_index points to an earlier hex, we do nothing.
 * The moving unit will only be updated if update is set to true; otherwise,
 * the provided unit is merely hidden during the movement and re-shown after.
 * (Not updating the unit can produce smoother animations in some cases.)
 * If @a wait is set to false, this returns without waiting for the final
 * animation to finish. Call wait_for_anims() to explicitly get this final
 * wait (another call to proceed_to() or finish() will implicitly wait). The
 * unit must remain valid until the wait is finished.
 */
void unit_mover::proceed_to(unit_ptr u, std::size_t path_index, bool update, bool wait)
{
    // Nothing to do here if animations cannot be shown.
    if ( !can_draw_ || !animate_ )
        return;

    // Handle pending visibility issues before introducing new ones.
    wait_for_anims();

    if ( update  ||  !temp_unit_ptr_ )
        // Replace the temp unit (which also hides u and shows our temporary).
        replace_temporary(u);
    else
    {
        // Just switch the display from the real unit to our fake one.
        temp_unit_ptr_->set_hidden(false);
        u->set_hidden(true);
    }

    // Safety check.
    path_index = std::min(path_index, path_.size()-1);

    for ( ; current_ < path_index; ++current_ ) {
        // It is possible for path_[current_] and path_[current_+1] not to be adjacent.
        // When that is the case, and the unit is invisible at path_[current_], we shouldn't
        // scroll to that hex.
        std::vector<map_location> locs;
        if (!temp_unit_ptr_->invisible(path_[current_]))
            locs.push_back(path_[current_]);
        if (!temp_unit_ptr_->invisible(path_[current_+1]))
            locs.push_back(path_[current_+1]);
        // If the unit can be seen by the viewing side while making this step:
        if ( !is_enemy_ || !locs.empty() )
        {
            // Wait for the previous step to complete before drawing the next one.
            wait_for_anims();

            if ( !disp_->tile_fully_on_screen(path_[current_]) ||
                 !disp_->tile_fully_on_screen(path_[current_+1]))
            {
                // prevent the unit from disappearing if we scroll here with i == 0
                temp_unit_ptr_->set_location(path_[current_]);
                disp_->invalidate(path_[current_]);
                // scroll in as much of the remaining path as possible
                if ( temp_unit_ptr_->anim_comp().get_animation() )
                    temp_unit_ptr_->anim_comp().get_animation()->pause_animation();
                disp_->scroll_to_tiles(locs, game_display::ONSCREEN,
                                       true, false, 0.0, force_scroll_);
                if ( temp_unit_ptr_->anim_comp().get_animation() )
                    temp_unit_ptr_->anim_comp().get_animation()->restart_animation();
            }

            if ( tiles_adjacent(path_[current_], path_[current_+1]) )
                wait_until_ =
                    move_unit_between(path_[current_], path_[current_+1],
                                      temp_unit_ptr_.get_unit_ptr(), current_,
                                      path_.size() - (current_+2), animator_,
                                      *disp_);
            else if ( path_[current_] != path_[current_+1] )
                teleport_unit_between(path_[current_], path_[current_+1],
                                      *temp_unit_ptr_, *disp_);
        }
    }

    // Update the unit's facing.
    u->set_facing(temp_unit_ptr_->facing());
    u->anim_comp().set_standing(false); // Need to reset u's animation so the new facing takes effect.
    // Remember the unit to unhide when the animation finishes.
    shown_unit_ = u;
    if ( wait )
        wait_for_anims();
}


/**
 * Waits for the final animation of the most recent proceed_to() to finish.
 * It is not necessary to call this unless you want to wait before the next
 * call to proceed_to() or finish().
 */
void unit_mover::wait_for_anims()
{
    if ( wait_until_ == INT_MAX )
        // Wait for end (not currently used, but still supported).
        animator_.wait_for_end();
    else if ( wait_until_ != INT_MIN ) {
        // Wait until the specified time (used for normal movement).
        animator_.wait_until(wait_until_);
        // debug code, see unit_frame::redraw()
        // std::cout << "   end\n";
        // TODO: For wesnoth 1.14+: check if efficient for redrawing?
        // Check with large animated units too make sure artifacts are
        // not left on screen after unit movement in particular.
        if ( disp_ ) { // Should always be true if we get here.
            // Invalidate the hexes around the move that prompted this wait.
            for(const map_location& adj : get_adjacent_tiles(path_[current_ - 1])) {
                disp_->invalidate(adj);
            }

            for(const map_location& adj : get_adjacent_tiles(path_[current_])) {
                disp_->invalidate(adj);
            }
        }
    }

    // Reset data.
    wait_until_ = INT_MIN;
    animator_.clear();

    update_shown_unit();
}


/**
 * Finishes the display of movement for the supplied unit.
 * If called before showing the unit reach the end of the path, it will be
 * assumed that the movement ended early.
 * If @a dir is not supplied, the final direction will be determined by (the
 * last two traversed hexes of) the path.
 */
void unit_mover::finish(unit_ptr u, map_location::DIRECTION dir)
{
    // Nothing to do here if the display is not valid.
    if ( !can_draw_ ) {
        // Make sure to reset the unit's animation to deal with a quirk in the
        // action engine where it leaves it to us to reenable bars even if the
        // display is initially locked.
        u->anim_comp().set_standing(true);
        return;
    }

    const map_location & end_loc = path_[current_];
    const map_location::DIRECTION final_dir = current_ == 0 ?
        path_[0].get_relative_dir(path_[1]) :
        path_[current_-1].get_relative_dir(end_loc);

    if ( animate_ )
    {
        wait_for_anims(); // In case proceed_to() did not wait for the last animation.

        // Make sure the displayed unit is correct.
        replace_temporary(u);
        temp_unit_ptr_->set_location(end_loc);
        temp_unit_ptr_->set_facing(final_dir);

        // Animation
        animator_.add_animation(temp_unit_ptr_.get_unit_ptr(), "post_movement", end_loc);
        animator_.start_animations();
        animator_.wait_for_end();
        animator_.clear();

        // Switch the display back to the real unit.
        u->set_hidden(was_hidden_);
        temp_unit_ptr_->set_hidden(true);

        if(events::mouse_handler* mousehandler = events::mouse_handler::get_singleton()) {
            mousehandler->invalidate_reachmap();
        }
    }
    else
    {
        // Show the unit at end of skipped animation
        u->set_hidden(was_hidden_);
    }

    // Facing gets set even when not animating.
    u->set_facing(dir == map_location::NDIRECTIONS ? final_dir : dir);
    u->anim_comp().set_standing(true);  // Need to reset u's animation so the new facing takes effect.

    // Redraw path ends (even if not animating).
    disp_->invalidate(path_.front());
    disp_->invalidate(end_loc);
}


/**
 * Display a unit moving along a given path.
 *
 * @param path     The path to traverse.
 * @param u        The unit to show being moved. Its facing will be updated,
 *                 but not its position.
 * @param animate  If set to false, only side-effects of move are applied
 *                 (correct unit facing, path hexes redrawing).
 * @param dir      Unit will be set facing this direction after move.
 *                 If nothing passed, direction will be set based on path.
 * @param force_scroll
 */
/* Note: Hide the unit in its current location,
 * but don't actually remove it until the move is done,
 * so that while the unit is moving status etc.
 * will still display the correct number of units.
 */
void move_unit(const std::vector<map_location>& path, unit_ptr u,
               bool animate, map_location::DIRECTION dir,
               bool force_scroll)
{
    unit_mover mover(path, animate, force_scroll);

    mover.start(u);
    mover.proceed_to(u, path.size());
    mover.finish(u, dir);
}


void reset_helpers(const unit *attacker,const unit *defender);

void unit_draw_weapon(const map_location& loc, unit& attacker,
        const_attack_ptr attack,const_attack_ptr secondary_attack, const map_location& defender_loc, unit_ptr defender)
{
    display* disp = display::get_singleton();
    if(do_not_show_anims(disp) || disp->fogged(loc) || !preferences::show_combat()) {
        return;
    }
    unit_animator animator;
    attacker.set_facing(loc.get_relative_dir(defender_loc));
    defender->set_facing(defender_loc.get_relative_dir(loc));
    animator.add_animation(attacker.shared_from_this(),"draw_weapon",loc,defender_loc,0,true,"",{0,0,0},strike_result::type::hit,attack,secondary_attack,0);
    if(defender) {
        animator.add_animation(defender,"draw_weapon",defender_loc,loc,0,true,"",{0,0,0},strike_result::type::miss,secondary_attack,attack,0);
    }
    animator.start_animations();
    animator.wait_for_end();

}


void unit_sheath_weapon(const map_location& primary_loc, unit_ptr primary_unit,
        const_attack_ptr primary_attack,const_attack_ptr secondary_attack, const map_location& secondary_loc,unit_ptr secondary_unit)
{
    display* disp = display::get_singleton();
    if(do_not_show_anims(disp) || disp->fogged(primary_loc) || !preferences::show_combat()) {
        return;
    }
    unit_animator animator;
    if(primary_unit) {
        animator.add_animation(primary_unit,"sheath_weapon",primary_loc,secondary_loc,0,true,"",{0,0,0},strike_result::type::invalid,primary_attack,secondary_attack,0);
    }
    if(secondary_unit) {
        animator.add_animation(secondary_unit,"sheath_weapon",secondary_loc,primary_loc,0,true,"",{0,0,0},strike_result::type::invalid,secondary_attack,primary_attack,0);
    }

    if(primary_unit || secondary_unit) {
        animator.start_animations();
        animator.wait_for_end();
    }
    if(primary_unit) {
        primary_unit->anim_comp().set_standing();
    }
    if(secondary_unit) {
        secondary_unit->anim_comp().set_standing();
    }
    reset_helpers(primary_unit.get(),secondary_unit.get());

}


void unit_die(const map_location& loc, unit& loser,
        const_attack_ptr attack,const_attack_ptr secondary_attack, const map_location& winner_loc, unit_ptr winner)
{
    display* disp = display::get_singleton();
    if(do_not_show_anims(disp) || disp->fogged(loc) || !preferences::show_combat()) {
        return;
    }
    unit_animator animator;
    // hide the hp/xp bars of the loser (useless and prevent bars around an erased unit)
    animator.add_animation(loser.shared_from_this(),"death",loc,winner_loc,0,false,"",{0,0,0},strike_result::type::kill,attack,secondary_attack,0);
    // but show the bars of the winner (avoid blinking and show its xp gain)
    if(winner) {
        animator.add_animation(winner,"victory",winner_loc,loc,0,true,"",{0,0,0},
            strike_result::type::kill,secondary_attack,attack,0);
    }
    animator.start_animations();
    animator.wait_for_end();

    reset_helpers(winner.get(), &loser);

    if(events::mouse_handler* mousehandler = events::mouse_handler::get_singleton()) {
        mousehandler->invalidate_reachmap();
    }
}


void unit_attack(display * disp, game_board & board,
                 const map_location& a, const map_location& b, int damage,
                 const attack_type& attack, const_attack_ptr secondary_attack,
                 int swing, const std::string& hit_text, int drain_amount,
                 const std::string& att_text,
                 const std::vector<std::string>* extra_hit_sounds,
                 bool attacking)
{
    if(do_not_show_anims(disp) || (disp->fogged(a) && disp->fogged(b)) || !preferences::show_combat()) {
        return;
    }
    //const unit_map& units = disp->get_units();
    disp->select_hex(map_location::null_location());

    // scroll such that there is at least half a hex spacing around fighters
    disp->scroll_to_tiles(a,b,game_display::ONSCREEN,true,0.5,false);

    log_scope("unit_attack");

    const unit_map::const_iterator att = board.units().find(a);
    assert(att.valid());
    const unit& attacker = *att;

    const unit_map::iterator def = board.find_unit(b);
    assert(def.valid());
    unit &defender = *def;
    int def_hitpoints = defender.hitpoints();
    const_attack_ptr weapon = attack.shared_from_this();
    auto ctx = weapon->specials_context(attacker.shared_from_this(), defender.shared_from_this(), a, b, attacking, secondary_attack);
    std::optional<decltype(ctx)> opp_ctx;

    if(secondary_attack) {
        opp_ctx.emplace(secondary_attack->specials_context(defender.shared_from_this(), attacker.shared_from_this(), b, a, !attacking, weapon));
    }

    att->set_facing(a.get_relative_dir(b));
    def->set_facing(b.get_relative_dir(a));
    defender.set_facing(b.get_relative_dir(a));

    std::string text = number_and_text(damage, hit_text);
    std::string text_2 = number_and_text(std::abs(drain_amount), att_text);

    strike_result::type hit_type;
    if(damage >= defender.hitpoints()) {
        hit_type = strike_result::type::kill;
    } else if(damage > 0) {
        hit_type = strike_result::type::hit;
    }else {
        hit_type = strike_result::type::miss;
    }

    unit_animator animator;

    animator.add_animation(attacker.shared_from_this(), "attack", att->get_location(), def->get_location(), damage, true, text_2,
        (drain_amount >= 0) ? color_t(0, 255, 0) : color_t(255, 0, 0), hit_type, weapon,
        secondary_attack, swing);

    // note that we take an anim from the real unit, we'll use it later
    const unit_animation* defender_anim = def->anim_comp().choose_animation(def->get_location(), "defend",
        att->get_location(), damage, hit_type, weapon, secondary_attack, swing);

    animator.add_animation(defender.shared_from_this(), defender_anim, def->get_location(), true, text, {255, 0, 0});

    unit_ability_list leadership_list = attacker.get_abilities_weapons("leadership", weapon, secondary_attack);
    unit_ability_list resistance_list = defender.get_abilities_weapons("resistance", secondary_attack, weapon);
    for(const unit_ability& ability : leadership_list) {
        if(ability.teacher_loc == a) {
            continue;
        }

        if(ability.teacher_loc == b) {
            continue;
        }

        unit_map::const_iterator leader = board.units().find(ability.teacher_loc);
        assert(leader.valid());
        leader->set_facing(ability.teacher_loc.get_relative_dir(a));
        leader->anim_comp().invalidate(*disp);
        animator.add_animation(leader.get_shared_ptr(), "leading", ability.teacher_loc,
            att->get_location(), damage, true,  "", {0,0,0},
            hit_type, weapon, secondary_attack, swing);
    }

    for(const unit_ability& ability : resistance_list) {
        if(ability.teacher_loc == a) {
            continue;
        }

        if(ability.teacher_loc == b) {
            continue;
        }

        unit_map::const_iterator helper = board.units().find(ability.teacher_loc);
        assert(helper.valid());
        helper->set_facing(ability.teacher_loc.get_relative_dir(b));
        animator.add_animation(helper.get_shared_ptr(), "resistance", ability.teacher_loc,
            def->get_location(), damage, true,  "", {0,0,0},
            hit_type, weapon, secondary_attack, swing);
    }

    unit_ability_list abilities = att->get_location();
    for(auto& special : attacker.checking_tags()) {
        abilities.append(weapon->get_weapon_ability(special));
    }

    for(const unit_ability& ability : abilities) {
        if(ability.teacher_loc == a) {
            continue;
        }

        if(ability.teacher_loc == b) {
            continue;
        }

        bool leading_playable = false;
        bool helping_playable = false;
        for(const unit_ability& leader_list : leadership_list) {
            if(ability.teacher_loc == leader_list.teacher_loc) {
                leading_playable = true;
                break;
            }
        }

        for(const unit_ability& helper_list : resistance_list) {
            if(ability.teacher_loc == helper_list.teacher_loc) {
                helping_playable = true;
                break;
            }
        }

        unit_map::const_iterator leader = board.units().find(ability.teacher_loc);
        assert(leader.valid());
        leader->set_facing(ability.teacher_loc.get_relative_dir(a));
        if(animator.has_animation(leader.get_shared_ptr(), "leading", ability.teacher_loc,
            att->get_location(), damage, hit_type, weapon, secondary_attack, swing) && leading_playable){
                continue;
        }
        if(animator.has_animation(leader.get_shared_ptr(), "resistance", ability.teacher_loc,
            def->get_location(), damage, hit_type, weapon, secondary_attack, swing) && helping_playable){
                continue;
        }
        animator.add_animation(leader.get_shared_ptr(), "teaching", ability.teacher_loc,
            att->get_location(), damage, true,  "", {0,0,0},
            hit_type, weapon, secondary_attack, swing);
    }


    animator.start_animations();
    animator.wait_until(0);
    int damage_left = damage;
    bool extra_hit_sounds_played = false;
    while(damage_left > 0 && !animator.would_end()) {
        if(!extra_hit_sounds_played && extra_hit_sounds != nullptr) {
            for (std::string hit_sound : *extra_hit_sounds) {
                sound::play_sound(hit_sound);
            }
            extra_hit_sounds_played = true;
        }

        int step_left = (animator.get_end_time() - animator.get_animation_time() )/50;
        if(step_left < 1) step_left = 1;
        int removed_hp =  damage_left/step_left ;
        if(removed_hp < 1) removed_hp = 1;
        defender.take_hit(removed_hp);
        damage_left -= removed_hp;
        animator.wait_until(animator.get_animation_time_potential() +50);
    }
    animator.wait_for_end();
    // pass the animation back to the real unit
    def->anim_comp().start_animation(animator.get_end_time(), defender_anim, true);
    reset_helpers(&*att, &*def);
    def->set_hitpoints(def_hitpoints);
}

// private helper function, set all helpers to default position
void reset_helpers(const unit *attacker,const unit *defender)
{
    display* disp = display::get_singleton();
    const unit_map& units = disp->get_units();
    if(attacker) {
        unit_ability_list attacker_abilities = attacker->get_abilities("leadership");
        for(auto& special : attacker->checking_tags()) {
            attacker_abilities.append(attacker->get_abilities(special));
        }
        for(const unit_ability& ability : attacker_abilities) {
            unit_map::const_iterator leader = units.find(ability.teacher_loc);
            assert(leader != units.end());
            leader->anim_comp().set_standing();
        }
    }

    if(defender) {
        unit_ability_list defender_abilities = defender->get_abilities("resistance");
        for(auto& special : defender->checking_tags()) {
            defender_abilities.append(defender->get_abilities(special));
        }
        for(const unit_ability& ability : defender_abilities) {
            unit_map::const_iterator helper = units.find(ability.teacher_loc);
            assert(helper != units.end());
            helper->anim_comp().set_standing();
        }
    }
}

void unit_recruited(const map_location& loc,const map_location& leader_loc)
{
    game_display* disp = game_display::get_singleton();
    if(do_not_show_anims(disp) || (disp->fogged(loc) && disp->fogged(leader_loc))) {
        return;
    }

    const display_context& dc = disp->get_disp_context();
    const team& viewing_team = dc.get_team(disp->viewing_side());

    unit_map::const_iterator u = disp->get_units().find(loc);
    if(u == disp->get_units().end()) return;
    const bool unit_visible = u->is_visible_to_team(viewing_team, false);

    unit_map::const_iterator leader = disp->get_units().find(leader_loc); // may be null_location
    const bool leader_visible = (leader != disp->get_units().end()) && leader->is_visible_to_team(viewing_team, false);

    unit_animator animator;

    {
        ON_SCOPE_EXIT(u) {
            u->set_hidden(false);
        };
        u->set_hidden(true);

        if (leader_visible && unit_visible) {
            disp->scroll_to_tiles(loc,leader_loc,game_display::ONSCREEN,true,0.0,false);
        } else if (leader_visible) {
            disp->scroll_to_tile(leader_loc,game_display::ONSCREEN,true,false);
        } else if (unit_visible) {
            disp->scroll_to_tile(loc,game_display::ONSCREEN,true,false);
        } else {
            return;
        }
        if (leader != disp->get_units().end()) {
            leader->set_facing(leader_loc.get_relative_dir(loc));
            if (leader_visible) {
                animator.add_animation(leader.get_shared_ptr(), "recruiting", leader_loc, loc, 0, true);
            }
        }
    }
    animator.add_animation(u.get_shared_ptr(), "recruited", loc, leader_loc);
    animator.start_animations();
    animator.wait_for_end();
    animator.set_all_standing();
    if (loc==disp->mouseover_hex()) disp->invalidate_unit();
}

void unit_healing(unit &healed, const std::vector<unit *> &healers, int healing,
                  const std::string & extra_text)
{
    game_display* disp = game_display::get_singleton();
    const map_location& healed_loc = healed.get_location();
    const bool some_healer_is_unfogged =
        (healers.end() != std::find_if_not(healers.begin(), healers.end(),
            [&](unit* h) { return disp->fogged(h->get_location()); }));

    if(do_not_show_anims(disp) || (disp->fogged(healed_loc) && !some_healer_is_unfogged)) {
        return;
    }

    // This is all the pretty stuff.
    disp->scroll_to_tile(healed_loc, game_display::ONSCREEN,true,false);
    disp->display_unit_hex(healed_loc);
    unit_animator animator;

    for (unit *h : healers) {
        h->set_facing(h->get_location().get_relative_dir(healed_loc));
        animator.add_animation(h->shared_from_this(), "healing", h->get_location(),
            healed_loc, healing);
    }

    if (healing < 0) {
        animator.add_animation(healed.shared_from_this(), "poisoned", healed_loc,
                               map_location::null_location(), -healing, false,
                               number_and_text(-healing, extra_text),
                               {255,0,0});
    } else if ( healing > 0 ) {
        animator.add_animation(healed.shared_from_this(), "healed", healed_loc,
                               map_location::null_location(), healing, false,
                               number_and_text(healing, extra_text),
                               {0,255,0});
    } else {
        animator.add_animation(healed.shared_from_this(), "healed", healed_loc,
                               map_location::null_location(), 0, false,
                               extra_text, {0,255,0});
    }
    animator.start_animations();
    animator.wait_for_end();
    animator.set_all_standing();
}

} // end unit_display namespace