Step 3 - Add User Control¶
Now we need to be able to get the user to move around.
First, at the top of the program add a constant that controls how many pixels per update our character travels:
# Movement speed of player, in pixels per frame
PLAYER_MOVEMENT_SPEED = 5
Next, at the end of our setup
method, we are need to create a physics engine that will
move our player and keep her from running through walls. The PhysicsEngineSimple
class takes two parameters: The moving
sprite, and a list of sprites the moving sprite can’t move through.
For more information about the physics engine we are using here, see PhysicsEngineSimple class
Note
It is possible to have multiple physics engines, one per moving sprite. These are very simple, but easy physics engines. See Pymunk Platformer for a more advanced physics engine.
# Movement speed of player, in pixels per frame
PLAYER_MOVEMENT_SPEED = 5
Each sprite has center_x
and center_y
attributes. Changing these will
change the location of the sprite. (There are also attributes for top, bottom,
left, right, and angle that will move the sprite.)
Each sprite has change_x
and change_y
variables. These can be used to
hold the velocity that the sprite is moving with. We will adjust these
based on what key the user hits. If the user hits the right arrow key
we want a positive value for change_x
. If the value is 5, it will move
5 pixels per frame.
In this case, when the user presses a key we’ll change the sprites change x and y. The physics engine will look at that, and move the player unless she’ll hit a wall.
1 def on_key_press(self, key, modifiers):
2 """Called whenever a key is pressed. """
3
4 if key == arcade.key.UP or key == arcade.key.W:
5 self.player_sprite.change_y = PLAYER_MOVEMENT_SPEED
6 elif key == arcade.key.DOWN or key == arcade.key.S:
7 self.player_sprite.change_y = -PLAYER_MOVEMENT_SPEED
8 elif key == arcade.key.LEFT or key == arcade.key.A:
9 self.player_sprite.change_x = -PLAYER_MOVEMENT_SPEED
10 elif key == arcade.key.RIGHT or key == arcade.key.D:
11 self.player_sprite.change_x = PLAYER_MOVEMENT_SPEED
On releasing the key, we’ll put our speed back to zero.
1 def on_key_release(self, key, modifiers):
2 """Called when the user releases a key. """
3
4 if key == arcade.key.UP or key == arcade.key.W:
5 self.player_sprite.change_y = 0
6 elif key == arcade.key.DOWN or key == arcade.key.S:
7 self.player_sprite.change_y = 0
8 elif key == arcade.key.LEFT or key == arcade.key.A:
9 self.player_sprite.change_x = 0
10 elif key == arcade.key.RIGHT or key == arcade.key.D:
11 self.player_sprite.change_x = 0
Note
This method of tracking the speed to the key the player presses is simple, but isn’t perfect. If the player hits both left and right keys at the same time, then lets off the left one, we expect the player to move right. This method won’t support that. If you want a slightly more complex method that does, see Better Move By Keyboard.
Our on_update
method is called about 60 times per second. We’ll ask the physics
engine to move our player based on her change_x
and change_y
.
1 def on_update(self, delta_time):
2 """ Movement and game logic """
3
4 # Move the player with the physics engine
5 self.physics_engine.update()