SDL_Surface* draw_line_to(const PointI& source, const PointI& target, const SDL_Color& colour){    using namespace Surface_Tools;    SDL_Surface* surface = NULL;    PointI p1, p2;    if(source.x < target.x)    {        p1.x = source.x;        p2.x = target.x;    }    else    {        p1.x = target.x;        p2.x = source.x;    }    if(source.y < target.y)    {        p1.y = source.y;        p2.y = target.y;    }    else    {        p1.y = target.y;        p2.y = source.y;    }        surface = create_blank_surface(p2 - p1);    bool steep = abs(p2.y - p1.y) > abs(p2.x - p1.x);    if(steep)    {        std::swap(p1.x, p1.y);        std::swap(p2.x, p2.y);    }    if(p1.x > p2.x)    {        std::swap(p1.x, p2.x);        std::swap(p1.y, p2.y);    }    int delta_x = p2.x - p1.x;    int delta_y = abs(p2.y - p1.y);    int error = delta_x / 2;    int y_step = 0;    int y = p1.y;    y_step = p1.y < p2.y ? 1 : -1;    for(int x = p1.x; x < p2.x; ++x)    {        if(steep)        {            set_pixel(surface, y, x, colour);        }        else        {            set_pixel(surface, x, y, colour);        }        error = error - delta_y;        if(error < 0)        {            y += y_step;            error += delta_x;        }    }    return surface;}

int main(int argc, char* argv[]){    Logger::Initialise("log.txt");    SDL_Systems::Initialise_SDL();    SDL_Systems::Initialise_Mixer(44100, MIX_DEFAULT_FORMAT, 2, 4096);    Surface_Cache::Initialise(SDL_Tools::Colours::WHITE);    SDL_Renderer renderer(640, 480, 24, "Test", SDL_Tools::Colours::BLACK);    SDL_Surface* x = draw_line_to(        to_point_type<float, int>(PointF(10.0f, 10.0f)),        to_point_type<float, int>(PointF(30.0f, 20.0f)),        SDL_Tools::colour(255, 0, 0));    Surface missile_sfc("missile.png", false);

SDL_Surface* Surface_Tools::create_blank_surface(const PointI& size, int depth){    using namespace SDL_Tools;    SDL_Surface* sfc = SDL_CreateRGBSurface(SDL_SWSURFACE, size.x, size.y, depth,        r_mask, g_mask, b_mask, a_mask);    if(!sfc)    {                throw LRE_Exception("SDL_CreateRGBSurface failed in create_blank_surface: " +            std::string(SDL_GetError()));    }    SDL_Surface* ret = SDL_DisplayFormat(sfc);    SDL_FreeSurface(sfc);    if(!ret)    {        throw LRE_Exception("Could not create surface in create_blank_surface: " +            std::string(SDL_GetError()));    }    return ret;}

friend const Point operator-(const Point& lhs, const Point& rhs)    {	    return Point(lhs.x - rhs.x, lhs.y - rhs.y);    }

SDL_Surface* create_blank_surface(const PointI& size, int depth = 32);

raw_surface_ptr Surface_Cache::Load_Surface(const boost_path& file_name,bool is_colour_key, Opt_SDL_Colour colour_key){    using namespace Surface_Tools;    std::string fn = boost::filesystem::complete(file_name).file_string();	raw_surface_ptr loaded;	raw_surface_ptr optimized;	Uint32 map_colour_key = 0;	loaded = make_raw_surface_ptr(IMG_Load(fn.c_str()));	if(loaded.get() == NULL && !fn.empty())	{		throw LRE_Exception(			"Surface at: " + fn + " failed to load.\nSDL: " + SDL_GetError());	}	optimized = make_raw_surface_ptr(SDL_DisplayFormat(loaded.get()));	if(optimized.get() == NULL)	{		throw LRE_Exception(			"Surface at: " + fn + " failed to optimise.\nSDL: " + SDL_GetError());	}	if(is_colour_key)	{        // Do we want user-specified colour key or default?        const SDL_Colour ckey = colour_key ? *colour_key : def_colour_key;		// Create the colour key.		map_colour_key = SDL_MapRGB(optimized->format, ckey.r, ckey.g, ckey.b);		// Sets the colour key to the Surface.		SDL_SetColorKey(optimized.get(), SDL_RLEACCEL | SDL_SRCCOLORKEY, map_colour_key);	}    fn_sfc_cache.insert(std::make_pair(file_name.file_string(), optimized));	LOG("Surface " + file_name.file_string() + " loaded.");	return optimized;}

loaded = make_raw_surface_ptr(IMG_Load(fn.c_str()));

set_pixel(surface, x, y, colour);

SDL_Surface* draw_line_to(const PointI& source, const PointI& target, const SDL_Color& colour){    using namespace Surface_Tools;    SDL_Surface* surface = NULL;    PointI p1, p2;    if(source.x < target.x)    {        p1.x = source.x;        p2.x = target.x;    }    else    {        p1.x = target.x;        p2.x = source.x;    }    if(source.y < target.y)    {        p1.y = source.y;        p2.y = target.y;    }    else    {        p1.y = target.y;        p2.y = source.y;    }    PointI diff(p2 - p1);    int largest_component = std::max<int>(diff.x, diff.y);    PointI sfc_size(largest_component, largest_component);        surface = create_blank_surface(sfc_size);    bool steep = abs(p2.y - p1.y) > abs(p2.x - p1.x);    if(steep)    {        std::swap(p1.x, p1.y);        std::swap(p2.x, p2.y);    }    if(p1.x > p2.x)    {        std::swap(p1.x, p2.x);        std::swap(p1.y, p2.y);    }    int delta_x = p2.x - p1.x;    int delta_y = abs(p2.y - p1.y);    int error = delta_x / 2;    int y_step = 0;    int y = p1.y;    y_step = p1.y < p2.y ? 1 : -1;    for(int x = p1.x; x < p2.x; ++x)    {        if(steep)        {            set_pixel(surface, y - p1.y, x - p1.x, colour);        }        else        {            set_pixel(surface, x - p1.x, y - p1.y, colour);        }        error = error - delta_y;        if(error < 0)        {            y += y_step;            error += delta_x;        }    }    return surface;}