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.physics_engine = arcade.PhysicsEnginePlatformer(
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
|
Note
You can change how the user jumps by changing the gravity and jump constants. Lower values for both will make for a more “floaty” character. Higher values make for a faster-paced game.
Source Code¶
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()
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