第5步-添加重力#

前面的例子很适合自上而下，但如果它是像我们的平台一样带有跳跃的侧视图呢？我们需要增加重力。首先，让我们定义一个常量来表示重力的加速度，一个常量来表示跳跃速度。

05_Add_gravity.py-添加重力#
GRAVITY = 1
PLAYER_JUMP_SPEED = 20

在结束时， setup 方法，将物理引擎更改为 PhysicsEnginePlatformer 并将重力作为一个参数。

05_Add_gravity.py-添加重力#
        # Create the 'physics engine'
        self.physics_engine = arcade.PhysicsEnginePlatformer(
            self.player_sprite, gravity_constant=GRAVITY, walls=self.scene["Walls"]
        )

我们正在发送我们的 SpriteList 对于玩家应该碰撞到的东西 walls 物理引擎的参数。正如我们将在后面的章节中看到的，Platform物理引擎有一个 platforms 和 walls 参数。这两者之间的区别非常重要。静态不移动精灵列表应始终发送到 walls 参数，并且移动的精灵应发送到 platforms 参数。确保您做到这一点将对性能有极大的好处。

通过添加静态精灵 platforms 参数大致是一个O(N)运算，这意味着随着您添加更多的精灵，性能将线性下降。如果将静态精灵添加到 walls 参数，那么它几乎是O(1)，并且例如100个和50,000个不移动的精灵之间基本上没有区别。

我们还在这里看到了一些与我们的 Scene 对象。您可以像访问Python词典一样访问场景，以便从中获取SpriteList。有多种方法可以访问场景中的SpriteList，但这是最简单、最直接的方法。您也可以使用 scene.get_sprite_list("My Layer") 。

然后，修改key down和key up事件处理程序。我们将删除之前的UP/DOWN语句，并在按下时进行“UP”跳转。

05_Add_gravity.py-添加重力#
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    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

注解

您可以通过更改重力和跳跃常量来更改用户的跳跃方式。两者的值越低，角色就越“漂浮”。值越高，游戏节奏越快。

源代码#

05_Add_gravity.py-添加重力#
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"""
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, gravity_constant=GRAVITY, walls=self.scene["Walls"]
        )

    def on_draw(self):
        """Render the screen."""

        # Clear the screen to the background color
        self.clear()

        # 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 function"""
    window = MyGame()
    window.setup()
    arcade.run()


if __name__ == "__main__":
    main()