Roguelike Tutorial, using python3+tdl, part 10
This is part of a series of tutorials; the main page can be found here.
The tutorial was written for tdl version 3.1.0.
Now that our game is bursting with gameplay potential, we can think about those little things that die-hard fans will surely miss during their long playing sessions. One of the most important is, of course, a save/load mechanism! This way they can go to sleep and dream about your scary monsters between play sessions.
To choose between continuing a previous game or starting a new one we need a main menu. But wait: our initialization logic and game loop are tightly bound, so they're not really prepared for these tasks. To avoid code duplication, we need to break them down into meaningful blocks (functions). We can then put them together to change between the menu and the game, start new games or load them, and even go to new dungeon levels. It's much easier than it sounds, so fear not!
Take a look at your initialization and game loop code, after all the functions. I can identify 3 blocks:
- System initialization (code between tdl.set_font and panel = ...).
- Setting up a new game (everything else except for the game loop).
- Starting the game loop.
The reason why I chose this separation is because I think they're the minimal blocks needed to do all the tasks. The system initialization must be done just once. Thinking out loud, here are outlines of all the tasks:
- Create a new game: set up the game, create map, start game loop. (This is what we have now.)
- Load game: load data (we won't deal with this block now), create map, start game loop.
- Advance level: set up new level (we won't deal with this block now), create map. (The game loop is already running and will just continue.)
Hopefully that will make at least some sense, it's not very detailed but gives us something to aim at.
The system initialization code will stay right where it is, it's the first thing the script executes. Now grab the rest of the code before the main loop and put it in a new function. The lines objects = [player], fov_recompute = True, player_action = None, and mouse_coord = (0, 0) will go elsewhere:
We have to declare some variables as global, since we're assigning them inside a function now.
Finally, the game loop, player_action = None, and mouse_coord = (0, 0) belong to their own function now, along with another instance of fov_recompute = True:
That was a lot of shuffling stuff around! Ok, just a couple of tiny changes left. Since the objects' list represents objects on the map, it makes sense to initialize it on map creation, so put it in make_map:
Finally, after system initialization you need to call the new functions to start playing:
That's it! The code is much tidier. If you don't care much about that, though, and prefer visible changes, then the next section is just for you!
To keep our main menu from appearing a bit bland, it would be pretty cool to show a neat background image below it. To do this, we'll have to borrow a function from libtcod-cffi. Starting with tdl version 3.1.0, libtcod-cffi's image functions can be used in tdl. It's one of tdl's dependencies, so it will already be installed on your system. Have a look at all the image-related functions here!
Of course, since tdl emulates a console, we can't directly show arbitrary images, since we can't access the console's pixels. We can, however, modify the background color of every console cell to match the color of a pixel from the image. The downside is that the image will be in a very low resolution. However, Jice came up with a neat trick: by using specialized characters, and modifying both foreground and background colors, we can double the resolution! This is called subcell resolution, and this page of the original libtcod docs shows some images of the effect (at the end of the page).
This means that, for our 80x50 cells console, we need a 160x100 pixels image. Here's the one I'm using, just download it and put it in your game's folder if you don't want to draw your own. I searched for real dungeon photos with a Creative Commons license using the advanced search in Yahoo Images (I tried it on Google Images too but didn't get as many results), then fired up Paint.net to resize it and modify it as much as possibly to give it the feel of a fantasy setting: torches, no natural light, a guy with a sword, that sort of stuff. I found that stacking layers and using a brush with an extremely low alpha (a value of 3 or so) lets me draw things very gradually, since I'm not exactly an artist! It guess it's OK to spend some time with this since it may be the only actual image in the whole game.
In your imports section, let's bring in libtcod-cffi's image_load function:
Right, after that small detour, it's back to coding! Let's create a function for the main menu interface, and begin by loading and showing the image:
It's really easy. Notice the file name is a bit different from the image I linked earlier. We can now take advantage of our reusable menu function to present 3 options: start game, continue, or quit. Since the function also returns if the player presses a different key (canceled), we need to wrap it in a loop to present the menu again in that situation.
Let's test this out! In the main script, instead of starting a new game right away with new_game() and play_game(), call our new function:
The main menu is working now, apart from the "continue" feature which we'll get to later. Now it's time to add some fluff. Before calling the menu function, I want to show my game's title and, of course, the author's name! You will probably want to modify this for your own game, of course.
You'll notice that the menu rectangle itself starts with a blank line. This is because the header string is empty, but this empty line causes the header to have a height of 1. To make that line go away, we need to check that condition in the menu function, between the lines header_height = ... and height = ....
Another detail is that the player may want to switch to fullscreen in the main menu. However, we only check that key during the game. It's fairly easy to copy that code to the menu function too, right after asking for the key:
Finally, extensive testing shows that starting a new game, going back to the main menu with Escape and starting another game results in a bug! In the second game, parts from the first are still visible. For the screen to always start black we need to clear the console in play_game(), right after fov_recompute = True.
There it is, a neat main menu, and with only a handful of lines of code!
Saving and loading
If you've tried it before in other languages, this probably sounds scary. It usually means tracing every last bit of state information in your game and cramming it into a raw stream of bytes. Not in Python -- the Pickle module is capable of doing that with only a few function calls!
But we can do even better by using the Shelve module: its interface is a simple dictionary. If you haven't used dictionaries before, check the Python tutorial on the subject. They're extremely useful, replacing lists in situations where you wish to index elements not by their position on the list, but by an arbitrary name, number, or any other key.
A Shelve allows you to store any object in a file, indexed by a string (for example, the original variable's name). So to store the map tiles and game objects in a file called "savegame", we only need to call:
I bet your jaw just dropped over how easy it is to save a game in Python; mine sure did the first time I learned this! Just rinse and repeat for all your game state variables, and don't forget to call close at the end. The Shelve module will recursively find everything referenced from these variables onwards, so tile instances referenced by the map will be saved, as well as components referenced by game objects, which in turn are referenced by the objects list.
The only quirk to keep in mind is when more than one variable references the same object. For example, the objects list references the player object, but the player variable also references it. Normally this doesn't present a problem, but the Shelve module doesn't keep track of shared references between different dictionary entries. So if you try this:
You'll get two player objects when you load! Because one instance will be saved by file['objects'] = objects and another by file['player'] = player. To avoid this we'll just save the index of the player in the list:
Here are a few more variables to keep. Also, don't forget to import shelve at the top of your code.
To automatically save when the player quits, call the new function in play_game, right before the break line:
That's all for saving. Loading follows the same procedure, except we assign to our variables the contents of the Shelve dictionary. Since we're assigning values to global variables, they need to be declared as such. The player_index we stored lets us assign the player variable to the correct object in the objects list. Having completely restored the core variables of the game, we can initialize the FOV map based on the loaded tiles.
We can now add new functionality to the main_menu function, so the player can actually continue a previous game! It needs to be wrapped in a try-except clause, because Shelve will throw an error if loading fails somehow (file doesn't exist, is corrupted, etc). If something goes wrong we just display a message about it and carry on. I also defined a new handy msgbox function for important messages like this.
And msgbox relies on the menu function entirely. We could call it directly instead of this msgbox, but in my opinion this makes code more readable by clearly conveying the intent (a message box instead of a list of options).
That concludes the code for the main menu, saving and loading. A nice side-effect is that if the player quits after dying and then tries to continue, the character will still be dead! (Because game_state == 'dead' .) So by saving to different files you could easily create "mortem" files so the player can remember previous lost games, which is pretty cool.
You can easily use the main menu as a template for other screens, like game options or character creation. And as you continually upgrade your game you'll sometimes have to add more state variables to the save/load functions; but hopefully with the Shelve module it won't be too bad. Keep an eye out for the quirk I talked about earlier, if you ever get duplicated objects or strange behavior after loading.
The whole code is available here.