Acceleration and Friction¶
sprite_move_keyboard_accel.py¶
1"""
2Show how to use acceleration and friction
3
4Artwork from http://kenney.nl
5
6If Python and Arcade are installed, this example can be run from the command line with:
7python -m arcade.examples.sprite_move_keyboard_accel
8"""
9
10import arcade
11import os
12
13SPRITE_SCALING = 0.5
14
15SCREEN_WIDTH = 800
16SCREEN_HEIGHT = 600
17SCREEN_TITLE = "Better Move Sprite with Keyboard Example"
18
19# Important constants for this example
20
21# Speed limit
22MAX_SPEED = 3.0
23
24# How fast we accelerate
25ACCELERATION_RATE = 0.1
26
27# How fast to slow down after we letr off the key
28FRICTION = 0.02
29
30class Player(arcade.Sprite):
31
32 def update(self):
33 self.center_x += self.change_x
34 self.center_y += self.change_y
35
36 # Check to see if we hit the screen edge
37 if self.left < 0:
38 self.left = 0
39 self.change_x = 0 # Zero x speed
40 elif self.right > SCREEN_WIDTH - 1:
41 self.right = SCREEN_WIDTH - 1
42 self.change_x = 0
43
44 if self.bottom < 0:
45 self.bottom = 0
46 self.change_y = 0
47 elif self.top > SCREEN_HEIGHT - 1:
48 self.top = SCREEN_HEIGHT - 1
49 self.change_y = 0
50
51
52class MyGame(arcade.Window):
53 """
54 Main application class.
55 """
56
57 def __init__(self, width, height, title):
58 """
59 Initializer
60 """
61
62 # Call the parent class initializer
63 super().__init__(width, height, title)
64
65 # Set the working directory (where we expect to find files) to the same
66 # directory this .py file is in. You can leave this out of your own
67 # code, but it is needed to easily run the examples using "python -m"
68 # as mentioned at the top of this program.
69 file_path = os.path.dirname(os.path.abspath(__file__))
70 os.chdir(file_path)
71
72 # Variables that will hold sprite lists
73 self.player_list = None
74
75 # Set up the player info
76 self.player_sprite = None
77
78 # Track the current state of what key is pressed
79 self.left_pressed = False
80 self.right_pressed = False
81 self.up_pressed = False
82 self.down_pressed = False
83
84 # Set the background color
85 arcade.set_background_color(arcade.color.AMAZON)
86
87 def setup(self):
88 """ Set up the game and initialize the variables. """
89
90 # Sprite lists
91 self.player_list = arcade.SpriteList()
92
93 # Set up the player
94 self.player_sprite = Player(":resources:images/animated_characters/female_person/femalePerson_idle.png", SPRITE_SCALING)
95 self.player_sprite.center_x = 50
96 self.player_sprite.center_y = 50
97 self.player_list.append(self.player_sprite)
98
99 def on_draw(self):
100 """
101 Render the screen.
102 """
103
104 # This command has to happen before we start drawing
105 arcade.start_render()
106
107 # Draw all the sprites.
108 self.player_list.draw()
109
110 # Display speed
111 arcade.draw_text(f"X Speed: {self.player_sprite.change_x:6.3f}", 10, 50, arcade.color.BLACK)
112 arcade.draw_text(f"Y Speed: {self.player_sprite.change_y:6.3f}", 10, 70, arcade.color.BLACK)
113
114 def on_update(self, delta_time):
115 """ Movement and game logic """
116
117 # Add some friction
118 if self.player_sprite.change_x > FRICTION:
119 self.player_sprite.change_x -= FRICTION
120 elif self.player_sprite.change_x < -FRICTION:
121 self.player_sprite.change_x += FRICTION
122 else:
123 self.player_sprite.change_x = 0
124
125 if self.player_sprite.change_y > FRICTION:
126 self.player_sprite.change_y -= FRICTION
127 elif self.player_sprite.change_y < -FRICTION:
128 self.player_sprite.change_y += FRICTION
129 else:
130 self.player_sprite.change_y = 0
131
132 # Apply acceleration based on the keys pressed
133 if self.up_pressed and not self.down_pressed:
134 self.player_sprite.change_y += ACCELERATION_RATE
135 elif self.down_pressed and not self.up_pressed:
136 self.player_sprite.change_y += -ACCELERATION_RATE
137 if self.left_pressed and not self.right_pressed:
138 self.player_sprite.change_x += -ACCELERATION_RATE
139 elif self.right_pressed and not self.left_pressed:
140 self.player_sprite.change_x += ACCELERATION_RATE
141
142 if self.player_sprite.change_x > MAX_SPEED:
143 self.player_sprite.change_x = MAX_SPEED
144 elif self.player_sprite.change_x < -MAX_SPEED:
145 self.player_sprite.change_x = -MAX_SPEED
146 if self.player_sprite.change_y > MAX_SPEED:
147 self.player_sprite.change_y = MAX_SPEED
148 elif self.player_sprite.change_y < -MAX_SPEED:
149 self.player_sprite.change_y = -MAX_SPEED
150
151 # Call update to move the sprite
152 # If using a physics engine, call update on it instead of the sprite
153 # list.
154 self.player_list.update()
155
156 def on_key_press(self, key, modifiers):
157 """Called whenever a key is pressed. """
158
159 if key == arcade.key.UP:
160 self.up_pressed = True
161 elif key == arcade.key.DOWN:
162 self.down_pressed = True
163 elif key == arcade.key.LEFT:
164 self.left_pressed = True
165 elif key == arcade.key.RIGHT:
166 self.right_pressed = True
167
168 def on_key_release(self, key, modifiers):
169 """Called when the user releases a key. """
170
171 if key == arcade.key.UP:
172 self.up_pressed = False
173 elif key == arcade.key.DOWN:
174 self.down_pressed = False
175 elif key == arcade.key.LEFT:
176 self.left_pressed = False
177 elif key == arcade.key.RIGHT:
178 self.right_pressed = False
179
180
181def main():
182 """ Main method """
183 window = MyGame(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_TITLE)
184 window.setup()
185 arcade.run()
186
187
188if __name__ == "__main__":
189 main()