Acceleration and Friction#
sprite_move_keyboard_accel.py#
1"""
2Acceleration and Friction
3
4Demonstrate how to implement simple acceleration and friction without a
5physics engine.
6
7Artwork from https://kenney.nl
8
9If Python and Arcade are installed, this example can be run from the
10command line with:
11python -m arcade.examples.sprite_move_keyboard_accel
12"""
13
14import arcade
15
16SPRITE_SCALING = 0.5
17
18SCREEN_WIDTH = 800
19SCREEN_HEIGHT = 600
20SCREEN_TITLE = "Better Move Sprite with Keyboard Example"
21
22# Important constants for this example
23
24# Speed limit
25MAX_SPEED = 3.0
26
27# How fast we accelerate
28ACCELERATION_RATE = 0.1
29
30# How fast to slow down after we let off the key
31FRICTION = 0.02
32
33
34class Player(arcade.Sprite):
35
36 def update(self):
37 self.center_x += self.change_x
38 self.center_y += self.change_y
39
40 # Check to see if we hit the screen edge
41 if self.left < 0:
42 self.left = 0
43 self.change_x = 0 # Zero x speed
44 elif self.right > SCREEN_WIDTH - 1:
45 self.right = SCREEN_WIDTH - 1
46 self.change_x = 0
47
48 if self.bottom < 0:
49 self.bottom = 0
50 self.change_y = 0
51 elif self.top > SCREEN_HEIGHT - 1:
52 self.top = SCREEN_HEIGHT - 1
53 self.change_y = 0
54
55
56class MyGame(arcade.Window):
57 """
58 Main application class.
59 """
60
61 def __init__(self, width, height, title):
62 """
63 Initializer
64 """
65
66 # Call the parent class initializer
67 super().__init__(width, height, title)
68
69 # Variable to will hold the player sprite list
70 self.player_list = None
71
72 # Create a place to store the player sprite
73 # so it can be accessed directly.
74 self.player_sprite = None
75
76 # Create places to store the speed display Text objects
77 self.x_speed_display = None
78 self.y_speed_display = None
79
80 # Track the current state of what key is pressed
81 self.left_pressed = False
82 self.right_pressed = False
83 self.up_pressed = False
84 self.down_pressed = False
85
86 # Set the background color
87 arcade.background_color = arcade.color.AMAZON
88
89 def setup(self):
90 """ Set up the game and initialize the variables. """
91
92 # Create a sprite list
93 self.player_list = arcade.SpriteList()
94
95 # Set up the player
96 self.player_sprite = Player(":resources:images/animated_characters/female_person/femalePerson_idle.png",
97 scale=SPRITE_SCALING)
98 self.player_sprite.position = self.width / 2, self.height / 2
99 self.player_list.append(self.player_sprite)
100
101 # Create the speed display objects with initial text
102 self.x_speed_display = arcade.Text(
103 f"X Speed: {self.player_sprite.change_x:6.3f}",
104 10, 50, arcade.color.BLACK)
105
106 self.y_speed_display = arcade.Text(
107 f"Y Speed: {self.player_sprite.change_y:6.3f}",
108 10, 70, arcade.color.BLACK)
109
110 def on_draw(self):
111 """
112 Render the screen.
113 """
114
115 # This command has to happen before we start drawing
116 self.clear()
117
118 # Draw all the sprites.
119 self.player_list.draw()
120
121 # Draw the speed indicators
122 self.x_speed_display.draw()
123 self.y_speed_display.draw()
124
125 def on_update(self, delta_time):
126 """ Movement and game logic """
127
128 # Add some friction
129 if self.player_sprite.change_x > FRICTION:
130 self.player_sprite.change_x -= FRICTION
131 elif self.player_sprite.change_x < -FRICTION:
132 self.player_sprite.change_x += FRICTION
133 else:
134 self.player_sprite.change_x = 0
135
136 if self.player_sprite.change_y > FRICTION:
137 self.player_sprite.change_y -= FRICTION
138 elif self.player_sprite.change_y < -FRICTION:
139 self.player_sprite.change_y += FRICTION
140 else:
141 self.player_sprite.change_y = 0
142
143 # Apply acceleration based on the keys pressed
144 if self.up_pressed and not self.down_pressed:
145 self.player_sprite.change_y += ACCELERATION_RATE
146 elif self.down_pressed and not self.up_pressed:
147 self.player_sprite.change_y += -ACCELERATION_RATE
148 if self.left_pressed and not self.right_pressed:
149 self.player_sprite.change_x += -ACCELERATION_RATE
150 elif self.right_pressed and not self.left_pressed:
151 self.player_sprite.change_x += ACCELERATION_RATE
152
153 if self.player_sprite.change_x > MAX_SPEED:
154 self.player_sprite.change_x = MAX_SPEED
155 elif self.player_sprite.change_x < -MAX_SPEED:
156 self.player_sprite.change_x = -MAX_SPEED
157 if self.player_sprite.change_y > MAX_SPEED:
158 self.player_sprite.change_y = MAX_SPEED
159 elif self.player_sprite.change_y < -MAX_SPEED:
160 self.player_sprite.change_y = -MAX_SPEED
161
162 # Call update to move the sprite
163 # IMPORTANT: If using a physics engine, you need to call update
164 # on it instead of the sprite list!
165 self.player_list.update()
166
167 # Update the speed displays based on the final speed
168 self.x_speed_display.text = f"X Speed: {self.player_sprite.change_x:6.3f}"
169 self.y_speed_display.text = f"Y Speed: {self.player_sprite.change_y:6.3f}"
170
171 def on_key_press(self, key, modifiers):
172 """Called whenever a key is pressed. """
173
174 if key == arcade.key.UP:
175 self.up_pressed = True
176 elif key == arcade.key.DOWN:
177 self.down_pressed = True
178 elif key == arcade.key.LEFT:
179 self.left_pressed = True
180 elif key == arcade.key.RIGHT:
181 self.right_pressed = True
182
183 def on_key_release(self, key, modifiers):
184 """Called when the user releases a key. """
185
186 if key == arcade.key.UP:
187 self.up_pressed = False
188 elif key == arcade.key.DOWN:
189 self.down_pressed = False
190 elif key == arcade.key.LEFT:
191 self.left_pressed = False
192 elif key == arcade.key.RIGHT:
193 self.right_pressed = False
194
195
196def main():
197 """ Main function """
198 window = MyGame(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_TITLE)
199 window.setup()
200 arcade.run()
201
202
203if __name__ == "__main__":
204 main()