# Step 5 - Add Gravity¶

The previous example great for top-down, but what if it is a side view with jumping like our platformer? We need to add gravity. First, let’s define a constant to represent the acceleration for gravity, and one for a jump speed.

```GRAVITY = 1
PLAYER_JUMP_SPEED = 20
```

At the end of the `setup` method, change the physics engine to `PhysicsEnginePlatformer` and include gravity as a parameter.

```        # Create the 'physics engine'
self.player_sprite, self.scene.get_sprite_list("Walls"), GRAVITY
)
```

Then, modify the key down and key up event handlers. We’ll remove the up/down statements we had before, and make ‘UP’ jump when pressed.

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18``` ``` def on_key_press(self, key, modifiers): """Called whenever a key is pressed.""" if key == arcade.key.UP or key == arcade.key.W: if self.physics_engine.can_jump(): self.player_sprite.change_y = PLAYER_JUMP_SPEED elif key == arcade.key.LEFT or key == arcade.key.A: self.player_sprite.change_x = -PLAYER_MOVEMENT_SPEED elif key == arcade.key.RIGHT or key == arcade.key.D: self.player_sprite.change_x = PLAYER_MOVEMENT_SPEED def on_key_release(self, key, modifiers): """Called when the user releases a key.""" if key == arcade.key.LEFT or key == arcade.key.A: self.player_sprite.change_x = 0 elif key == arcade.key.RIGHT or key == arcade.key.D: self.player_sprite.change_x = 0 ```
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123``` ```""" Platformer Game """ import arcade # Constants SCREEN_WIDTH = 1000 SCREEN_HEIGHT = 650 SCREEN_TITLE = "Platformer" # Constants used to scale our sprites from their original size CHARACTER_SCALING = 1 TILE_SCALING = 0.5 # Movement speed of player, in pixels per frame PLAYER_MOVEMENT_SPEED = 5 GRAVITY = 1 PLAYER_JUMP_SPEED = 20 class MyGame(arcade.Window): """ Main application class. """ def __init__(self): # Call the parent class and set up the window super().__init__(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_TITLE) # Our Scene Object self.scene = None # Separate variable that holds the player sprite self.player_sprite = None # Our physics engine self.physics_engine = None arcade.set_background_color(arcade.csscolor.CORNFLOWER_BLUE) def setup(self): """Set up the game here. Call this function to restart the game.""" # Initialize Scene self.scene = arcade.Scene() # Set up the player, specifically placing it at these coordinates. image_source = ":resources:images/animated_characters/female_adventurer/femaleAdventurer_idle.png" self.player_sprite = arcade.Sprite(image_source, CHARACTER_SCALING) self.player_sprite.center_x = 64 self.player_sprite.center_y = 128 self.scene.add_sprite("Player", self.player_sprite) # Create the ground # This shows using a loop to place multiple sprites horizontally for x in range(0, 1250, 64): wall = arcade.Sprite(":resources:images/tiles/grassMid.png", TILE_SCALING) wall.center_x = x wall.center_y = 32 self.scene.add_sprite("Walls", wall) # Put some crates on the ground # This shows using a coordinate list to place sprites coordinate_list = [[512, 96], [256, 96], [768, 96]] for coordinate in coordinate_list: # Add a crate on the ground wall = arcade.Sprite( ":resources:images/tiles/boxCrate_double.png", TILE_SCALING ) wall.position = coordinate self.scene.add_sprite("Walls", wall) # Create the 'physics engine' self.physics_engine = arcade.PhysicsEnginePlatformer( self.player_sprite, self.scene.get_sprite_list("Walls"), GRAVITY ) def on_draw(self): """Render the screen.""" # Clear the screen to the background color arcade.start_render() # Draw our Scene self.scene.draw() def on_key_press(self, key, modifiers): """Called whenever a key is pressed.""" if key == arcade.key.UP or key == arcade.key.W: if self.physics_engine.can_jump(): self.player_sprite.change_y = PLAYER_JUMP_SPEED elif key == arcade.key.LEFT or key == arcade.key.A: self.player_sprite.change_x = -PLAYER_MOVEMENT_SPEED elif key == arcade.key.RIGHT or key == arcade.key.D: self.player_sprite.change_x = PLAYER_MOVEMENT_SPEED def on_key_release(self, key, modifiers): """Called when the user releases a key.""" if key == arcade.key.LEFT or key == arcade.key.A: self.player_sprite.change_x = 0 elif key == arcade.key.RIGHT or key == arcade.key.D: self.player_sprite.change_x = 0 def on_update(self, delta_time): """Movement and game logic""" # Move the player with the physics engine self.physics_engine.update() def main(): """Main method""" window = MyGame() window.setup() arcade.run() if __name__ == "__main__": main() ```