Part 2 - The generic Entity, the render functions, and the map

Now that we can move our little ‘@’ symbol around, we need to give it something to move around in. But before that, let’s stop for a moment and think about the player object itself.

Right now, we just represent the player with the ‘@’ symbol, and its x and y coordinates. Shouldn’t we tie those things together in an object, along with some other data and functions that pertain to it?

Let’s create a generic class to represent not just the player, but just about everything in our game world. Enemies, items, and whatever other foreign entities we can dream of will be part of this class, which we’ll call Entity.

Create a new file, and call it entity.py. In that file, put the following class:

class Entity:
    """
    A generic object to represent players, enemies, items, etc.
    """
    def __init__(self, x, y, char, color):
        self.x = x
        self.y = y
        self.char = char
        self.color = color

    def move(self, dx, dy):
        # Move the entity by a given amount
        self.x += dx
        self.y += dy

This is pretty self explanatory. The Entity class holds the x and y coordinates, along with the character (the ‘@’ symbol in the player’s case) and the color (white for the player by default). We also have a method called move, which will allow the entity to be moved around by a given x and y.

Let’s put our fancy new class into action! Modify the first part of engine.py to look like this:

import tcod as libtcod

+from entity import Entity
from input_handlers import handle_keys


def main():
    screen_width = 80
    screen_height = 50

-   player_x = int(screen_width / 2)
-   player_y = int(screen_height / 2)

+   player = Entity(int(screen_width / 2), int(screen_height / 2), '@', libtcod.white)
+   npc = Entity(int(screen_width / 2 - 5), int(screen_height / 2), '@', libtcod.yellow)
+   entities = [npc, player]
    ...

import tcod as libtcod

from entity import Entity
from input_handlers import handle_keys


def main():
    screen_width = 80
    screen_height = 50

    player_x = int(screen_width / 2)
    player_y = int(screen_height / 2)

    player = Entity(int(screen_width / 2), int(screen_height / 2), '@', libtcod.white)
    npc = Entity(int(screen_width / 2 - 5), int(screen_height / 2), '@', libtcod.yellow)
    entities = [npc, player]
    ...

We’re importing the Entity class into engine.py, and using it to initialize the player and a new NPC. We store these two in a list, that will eventually hold all our entities on the map.

Also modify the part where we handle movement so that the Entity class handles the actual movement.

        if move:
            dx, dy = move
-           player_x += dx
-           player_x += dy
+           player.move(dx, dy)

        if move:
            dx, dy = move
            player_x += dx
            player_x += dy
            player.move(dx, dy)

Lastly, update the drawing functions to use the new player object:

    while not libtcod.console_is_window_closed():
        libtcod.sys_check_for_event(libtcod.EVENT_KEY_PRESS, key, mouse)

        libtcod.console_set_default_foreground(con, libtcod.white)
-       libtcod.console_put_char(con, player_x, player_y, '@', libtcod.BKGND_NONE)
+       libtcod.console_put_char(con, player.x, player.y, '@', libtcod.BKGND_NONE)
        libtcod.console_blit(con, 0, 0, screen_width, screen_height, 0, 0, 0)
        libtcod.console_flush()

-       libtcod.console_put_char(con, player_x, player_y, ' ', libtcod.BKGND_NONE)
+       libtcod.console_put_char(con, player.x, player.y, ' ', libtcod.BKGND_NONE)

        action = handle_keys(key)

    while not libtcod.console_is_window_closed():
        libtcod.sys_check_for_event(libtcod.EVENT_KEY_PRESS, key, mouse)

        libtcod.console_set_default_foreground(con, libtcod.white)
        libtcod.console_put_char(con, player_x, player_y, '@', libtcod.BKGND_NONE)
        libtcod.console_put_char(con, player.x, player.y, '@', libtcod.BKGND_NONE)
        libtcod.console_blit(con, 0, 0, screen_width, screen_height, 0, 0, 0)
        libtcod.console_flush()

        libtcod.console_put_char(con, player_x, player_y, ' ', libtcod.BKGND_NONE)
        libtcod.console_put_char(con, player.x, player.y, ' ', libtcod.BKGND_NONE)

        action = handle_keys(key)

Now we need to alter the way that the entities are drawn to the screen. If you run the code right now, only the player gets drawn. Let’s write some functions to draw not only the player, but any entity currently in our entities list.

Create a new file called render_functions.py. This will hold our functions for drawing and clearing from the screen. Put the following code in that file.

import tcod as libtcod


def render_all(con, entities, screen_width, screen_height):
    # Draw all entities in the list
    for entity in entities:
        draw_entity(con, entity)

    libtcod.console_blit(con, 0, 0, screen_width, screen_height, 0, 0, 0)


def clear_all(con, entities):
    for entity in entities:
        clear_entity(con, entity)


def draw_entity(con, entity):
    libtcod.console_set_default_foreground(con, entity.color)
    libtcod.console_put_char(con, entity.x, entity.y, entity.char, libtcod.BKGND_NONE)


def clear_entity(con, entity):
    # erase the character that represents this object
    libtcod.console_put_char(con, entity.x, entity.y, ' ', libtcod.BKGND_NONE)

Here’s a quick breakdown of what these functions do:

  • The render_all function is what we’ll call from our game loop to draw entities and, shortly, the map. For now, it takes the console (con), a list of entities, and the screen width/height as parameters, and calls the draw_entity function on each. It then blits the changes to the screen.
  • draw_entity is what does the actual drawing. The code should look very similar to what’s in our game loop right now, except it’s using the entity’s variables (x, y, char, and color) to do the drawing. This makes it flexible enough to, theoretically, draw any entity we pass to it.
  • clear_all is what we’ll use to clear all the entities after drawing them to the screen. It’s just a loop that calls another function.
  • clear_entity just does what our previous line did, and clears the entity from the screen (so that when it moves, it doesn’t leave a trail behind).

Now that we’ve gotten a few functions to assist drawing the entities, let’s put them to use. Make the following modifications to the section where we drew the player (in engine.py).

        ...
    libtcod.sys_check_for_event(libtcod.EVENT_KEY_PRESS, key, mouse)

-   libtcod.console_set_default_foreground(con, libtcod.white)
-   libtcod.console_put_char(con, player.x, player.y, '@', libtcod.BKGND_NONE)
-   libtcod.console_blit(con, 0, 0, screen_width, screen_height, 0, 0, 0)
+   render_all(con, entities, screen_width, screen_height)

    libtcod.console_flush()

-   libtcod.console_put_char(con, player.x, player.y, ' ', libtcod.BKGND_NONE)
+   clear_all(con, entities)

    action = handle_keys(key)
    ...

        ...
    libtcod.sys_check_for_event(libtcod.EVENT_KEY_PRESS, key, mouse)

    libtcod.console_set_default_foreground(con, libtcod.white)
    libtcod.console_put_char(con, player.x, player.y, '@', libtcod.BKGND_NONE)
    libtcod.console_blit(con, 0, 0, screen_width, screen_height, 0, 0, 0)
    render_all(con, entities, screen_width, screen_height)

    libtcod.console_flush()

    libtcod.console_put_char(con, player.x, player.y, ' ', libtcod.BKGND_NONE)
    clear_all(con, entities)

    action = handle_keys(key)
    ...

Don’t forget to import render_all and clear_all at the top of your file. Your imports section should now look something like this:

import tcod as libtcod

from entity import Entity
from input_handlers import handle_keys
+from render_functions import clear_all, render_all

import tcod as libtcod

from entity import Entity
from input_handlers import handle_keys
from render_functions import clear_all, render_all

If you run the project now, you should see your ‘@’ symbol, along with a yellow one representing our NPC. It doesn’t do anything, yet, but now we have a method for drawing more than one character to the screen.

It’s time to shift gears a bit and get our map in place. The map will consist of a 2d array of Tile objects. Tiles will have a few properties that define whether we can move through them, or see through them.

We’d better start by defining the size of our map. Add these variables right below where you defined the screen width and height:

    ...
    screen_height = 50
+   map_width = 80
+   map_height = 45

    ...
    screen_height = 50
    map_width = 80
    map_height = 45

Simple enough. Now we need a place for our Tile class, along with a few other map classes, to live. I prefer to keep similar classes in the same folder, so create a new Python package (that’s a directory with a file called __init__.py in it, __init__.py is empty in this case) called map_objects. In there, create a file called tile.py and put the following code in it.

class Tile:
    """
    A tile on a map. It may or may not be blocked, and may or may not block sight.
    """
    def __init__(self, blocked, block_sight=None):
        self.blocked = blocked

        # By default, if a tile is blocked, it also blocks sight
        if block_sight is None:
            block_sight = blocked

        self.block_sight = block_sight

Nothing too complicated here. The Tile class holds whether or not the tile is blocked (if it’s blocked, you can’t move through it), and whether or not it blocks sight (for our FOV algorithm later). Notice that you don’t have to pass block_sight every time; it’s assumed to be the same as blocked. By keeping the two separate, we can have a tile that can be seen-through, but not crossed (a lava pit maybe?), or vice versa (a dark room perhaps).

Now that we have the tile class, we need some sort of container to hold our tiles. Let’s call this class GameMap, which will hold the 2d array of tiles and some methods for setting up and interacting with it. Create a file (in the map_objects folder) and call it game_map.py, and put the following in it:

from map_objects.tile import Tile


class GameMap:
    def __init__(self, width, height):
        self.width = width
        self.height = height
        self.tiles = self.initialize_tiles()

    def initialize_tiles(self):
        tiles = [[Tile(False) for y in range(self.height)] for x in range(self.width)]

        tiles[30][22].blocked = True
        tiles[30][22].block_sight = True
        tiles[31][22].blocked = True
        tiles[31][22].block_sight = True
        tiles[32][22].blocked = True
        tiles[32][22].block_sight = True

        return tiles

We’re passing in the width and height of the map (which we’ve defined in our engine), and initializing a 2d array of Tiles, set to non-blocking by default. We’re setting a few tiles as blocked, just for demonstration purposes. I’ve kept the code setting the tiles up out of the __init__ function, for two reasons. One, it may get called outside the initialization, and two, because I prefer keeping __init__ functions as simple as possible.

Go back to engine.py, where we’ll make a few changes so that our map get initialized and then drawn to the screen.

Firstly, we need to define what colors to draw for blocked and non-blocked tiles. Let’s set up a dictionary that holds the colors we’ll be using for now (it will expand as this tutorial goes on).

    ...
    map_height = 45

+   colors = {
+       'dark_wall': libtcod.Color(0, 0, 100),
+       'dark_ground': libtcod.Color(50, 50, 150)
+   }

    player = Entity(int(screen_width / 2), int(screen_height / 2), '@', libtcod.white)

    ...
    map_height = 45

    colors = {
        'dark_wall': libtcod.Color(0, 0, 100),
        'dark_ground': libtcod.Color(50, 50, 150)
    }

    player = Entity(int(screen_width / 2), int(screen_height / 2), '@', libtcod.white)

These colors will serve as our wall and ground outside the FOV, when we get there (hence the ‘dark’ in the names).

Now let’s initialize the game map itself. This can go anywhere before the main loop; I put mine right below the console initialization.

    con = libtcod.console_new(screen_width, screen_height)

+   game_map = GameMap(map_width, map_height)

    key = libtcod.Key()

    con = libtcod.console_new(screen_width, screen_height)

    game_map = GameMap(map_width, map_height)

    key = libtcod.Key()

Don’t forget to import the actual GameMap object so that we can use it in the engine.

from entity import Entity
from input_handlers import handle_keys
+from map_objects.game_map import GameMap
from render_functions import clear_all, render_all

from entity import Entity
from input_handlers import handle_keys
from map_objects.game_map import GameMap
from render_functions import clear_all, render_all

Now that our map object is ready to go, let’s pass it to render_all so that we can draw it. We’ll also pass the colors dictionary, because render_all will need to know what colors to draw the various parts of the map. Note that the order in which you pass these arguments doesn’t matter, it just has to match in the function definition and when you call it.

-       render_all(con, entities, screen_width, screen_height)
+       render_all(con, entities, game_map, screen_width, screen_height, colors)

        render_all(con, entities, screen_width, screen_height)
        render_all(con, entities, game_map, screen_width, screen_height, colors)

Open up render_functions.py and modify render_all like this:

-def render_all(con, entities, screen_width, screen_height):
+def render_all(con, entities, game_map, screen_width, screen_height, colors):
+   # Draw all the tiles in the game map
+   for y in range(game_map.height):
+       for x in range(game_map.width):
+           wall = game_map.tiles[x][y].block_sight
+
+           if wall:
+               libtcod.console_set_char_background(con, x, y, colors.get('dark_wall'), libtcod.BKGND_SET)
+           else:
+               libtcod.console_set_char_background(con, x, y, colors.get('dark_ground'), libtcod.BKGND_SET)
+
    # Draw all entities in the list
    for entity in entities:
        draw_entity(con, entity)

    libtcod.console_blit(con, 0, 0, screen_width, screen_height, 0, 0, 0)

def render_all(con, entities, screen_width, screen_height):
def render_all(con, entities, game_map, screen_width, screen_height, colors):
    # Draw all the tiles in the game map
    for y in range(game_map.height):
        for x in range(game_map.width):
            wall = game_map.tiles[x][y].block_sight

            if wall:
                libtcod.console_set_char_background(con, x, y, colors.get('dark_wall'), libtcod.BKGND_SET)
            else:
                libtcod.console_set_char_background(con, x, y, colors.get('dark_ground'), libtcod.BKGND_SET)
    
    # Draw all entities in the list
    for entity in entities:
        draw_entity(con, entity)

    libtcod.console_blit(con, 0, 0, screen_width, screen_height, 0, 0, 0)

render_all now loops through each tile in the game map, and checks if it blocks sight or not. If it does, then it draws it as a wall, and if not, it draws a floor.

Run the project now, and you should see the ‘map’ drawn with some color to it. You’ll see our three block wall as well, but there’s one problem: We can move through the wall!

We need to add two more things before we can call it a day. Modify the part where the player’s move function gets called to look like this:

        if move:
            dx, dy = move

+           if not game_map.is_blocked(player.x + dx, player.y + dy):
+               player.move(dx, dy)
-           player.move(dx, dy)

        if move:
            dx, dy = move

            if not game_map.is_blocked(player.x + dx, player.y + dy):
                player.move(dx, dy)
            player.move(dx, dy)

* Note the indentation change for player.move(dx, dy). This is Python, so indentation matters!

Now we just have to create the is_blocked method in the game map. Open up the game_map.py file and add this method to the class:

    def is_blocked(self, x, y):
        if self.tiles[x][y].blocked:
            return True

        return False

* Note: You could shorten the is_blocked function, by simply writing return self.tiles[x][y].blocked. But we’ll be modifying this function to do more checks soon, hence we’re taking the more explicit route.

Run the project again, and you will get stuck on the walls.

That’s going to do it for this tutorial. It may not look like much, but we’ve set ourselves up to create some real looking dungeons in the next tutorial.

If you want to see the code so far in its entirety, click here.

Click here to move on to the next part of this tutorial.