static void shrink_cache()
{
#ifdef DEBUG_MINIMAP_CACHE
	std::cerr << "\nShrink cache from " << cache.size();
#else
	DBG_GUI_D << "Shrinking the minimap cache.\n";
#endif

	std::vector<std::pair<unsigned, tcache::iterator> > items;
	for(tcache::iterator itor = cache.begin(); itor != cache.end(); ++itor) {

		itor->second.age /= 2;
		items.push_back(std::make_pair(itor->second.age, itor));
	}

	std::partial_sort(items.begin()
			, items.begin() + cache_max_size / 4
			, items.end()
			, compare);

	for(std::vector<std::pair<unsigned, tcache::iterator> >::iterator
			  vitor = items.begin()
			; vitor < items.begin() + cache_max_size / 4
			; ++vitor) {

		cache.erase(vitor->second);
	}

#ifdef DEBUG_MINIMAP_CACHE
	std::cerr << " to " << cache.size() << ".\n";
#endif
}

const surface tminimap::get_image(const int w, const int h) const
{
	if(!terrain_) {
		return NULL;
	}

	if(terrain_ != terrain) {
#ifdef DEBUG_MINIMAP_CACHE
		std::cerr << "\nFlush cache.\n";
#else
		DBG_GUI_D << "Flushing the minimap cache.\n";
#endif
		terrain = terrain_;
		cache.clear();
	}

	const tkey key(w, h, map_data_);
	tcache::iterator itor = cache.find(key);

	if(itor != cache.end()) {
#ifdef DEBUG_MINIMAP_CACHE
		std::cerr << '+';
#endif
		itor->second.age++;
		return itor->second.surf;
	}

	if(cache.size() >= cache_max_size) {
		shrink_cache();
	}

	try
	{
		const gamemap map(boost::make_shared<terrain_type_data>(*terrain_), map_data_);
		const surface surf = image::getMinimap(w, h, map, NULL);
		cache.insert(std::make_pair(key, tvalue(surf)));
#ifdef DEBUG_MINIMAP_CACHE
		std::cerr << '-';
#endif
		return surf;
	}
	catch(incorrect_map_format_error& e)
	{
		ERR_CF << "Error while loading the map: " << e.message << '\n';
#ifdef DEBUG_MINIMAP_CACHE
		std::cerr << 'X';
#endif
	}
	return NULL;
}