Pymunk Physics Engine - Stacks of Boxes

This uses the Pymunk physics engine to manage stacks of boxes. The user can interact with the boxes using the mouse.

Screen shot of stacks of boxes.
pymunk_box_stacks.py
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"""
Use Pymunk physics engine.

For more info on Pymunk see:
http://www.pymunk.org/en/latest/

To install pymunk:
pip install pymunk

Artwork from http://kenney.nl

If Python and Arcade are installed, this example can be run from the command line with:
python -m arcade.examples.pymunk_box_stacks

Click and drag with the mouse to move the boxes.
"""

import arcade
import pymunk
import timeit
import math
import os

SCREEN_WIDTH = 1200
SCREEN_HEIGHT = 800


class PhysicsSprite(arcade.Sprite):
    def __init__(self, pymunk_shape, filename):
        super().__init__(filename, center_x=pymunk_shape.body.position.x, center_y=pymunk_shape.body.position.y)
        self.pymunk_shape = pymunk_shape


class CircleSprite(PhysicsSprite):
    def __init__(self, pymunk_shape, filename):
        super().__init__(pymunk_shape, filename)
        self.width = pymunk_shape.radius * 2
        self.height = pymunk_shape.radius * 2


class BoxSprite(PhysicsSprite):
    def __init__(self, pymunk_shape, filename, width, height):
        super().__init__(pymunk_shape, filename)
        self.width = width
        self.height = height


class MyGame(arcade.Window):
    """ Main application class. """

    def __init__(self, width, height):
        super().__init__(width, height)

        # Set the working directory (where we expect to find files) to the same
        # directory this .py file is in. You can leave this out of your own
        # code, but it is needed to easily run the examples using "python -m"
        # as mentioned at the top of this program.
        file_path = os.path.dirname(os.path.abspath(__file__))
        os.chdir(file_path)

        arcade.set_background_color(arcade.color.DARK_SLATE_GRAY)

        # -- Pymunk
        self.space = pymunk.Space()
        self.space.gravity = (0.0, -900.0)

        # Lists of sprites or lines
        self.sprite_list = arcade.SpriteList()
        self.static_lines = []

        # Used for dragging shapes aruond with the mouse
        self.shape_being_dragged = None
        self.last_mouse_position = 0, 0

        self.draw_time = 0
        self.processing_time = 0

        # Create the floor
        floor_height = 80
        body = pymunk.Body(body_type=pymunk.Body.STATIC)
        shape = pymunk.Segment(body, [0, floor_height], [SCREEN_WIDTH, floor_height], 0.0)
        shape.friction = 10
        self.space.add(shape)
        self.static_lines.append(shape)

        # Create the stacks of boxes
        for x in range(6):
            for y in range(12):
                size = 45
                mass = 12.0
                moment = pymunk.moment_for_box(mass, (size, size))
                body = pymunk.Body(mass, moment)
                body.position = pymunk.Vec2d(300 + x*50, (floor_height + size / 2) + y * (size + .01))
                shape = pymunk.Poly.create_box(body, (size, size))
                shape.friction = 0.3
                self.space.add(body, shape)

                sprite = BoxSprite(shape, "images/boxCrate_double.png", width=size, height=size)
                self.sprite_list.append(sprite)

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

        # This command has to happen before we start drawing
        arcade.start_render()

        # Start timing how long this takes
        draw_start_time = timeit.default_timer()

        # Draw all the sprites
        self.sprite_list.draw()

        # Draw the lines that aren't sprites
        for line in self.static_lines:
            body = line.body

            pv1 = body.position + line.a.rotated(body.angle)
            pv2 = body.position + line.b.rotated(body.angle)
            arcade.draw_line(pv1.x, pv1.y, pv2.x, pv2.y, arcade.color.WHITE, 2)

        # Display timings
        output = f"Processing time: {self.processing_time:.3f}"
        arcade.draw_text(output, 20, SCREEN_HEIGHT - 20, arcade.color.WHITE, 12)

        output = f"Drawing time: {self.draw_time:.3f}"
        arcade.draw_text(output, 20, SCREEN_HEIGHT - 40, arcade.color.WHITE, 12)

        self.draw_time = timeit.default_timer() - draw_start_time

    def on_mouse_press(self, x, y, button, modifiers):
        if button == arcade.MOUSE_BUTTON_LEFT:
            self.last_mouse_position = x, y
            # See if we clicked on anything
            shape_list = self.space.point_query((x, y), 1, pymunk.ShapeFilter())

            # If we did, remember what we clicked on
            if len(shape_list) > 0:
                self.shape_being_dragged = shape_list[0]

        elif button == arcade.MOUSE_BUTTON_RIGHT:
            # With right mouse button, shoot a heavy coin fast.
            mass = 60
            radius = 10
            inertia = pymunk.moment_for_circle(mass, 0, radius, (0, 0))
            body = pymunk.Body(mass, inertia)
            body.position = x, y
            body.velocity = 2000, 0
            shape = pymunk.Circle(body, radius, pymunk.Vec2d(0, 0))
            shape.friction = 0.3
            self.space.add(body, shape)

            sprite = CircleSprite(shape, "images/coin_01.png")
            self.sprite_list.append(sprite)

    def on_mouse_release(self, x, y, button, modifiers):
        if button == arcade.MOUSE_BUTTON_LEFT:
            # Release the item we are holding (if any)
            self.shape_being_dragged = None

    def on_mouse_motion(self, x, y, dx, dy):
        if self.shape_being_dragged is not None:
            # If we are holding an object, move it with the mouse
            self.last_mouse_position = x, y
            self.shape_being_dragged.shape.body.position = self.last_mouse_position
            self.shape_being_dragged.shape.body.velocity = dx * 20, dy * 20

    def update(self, delta_time):
        start_time = timeit.default_timer()

        # Check for balls that fall off the screen
        for sprite in self.sprite_list:
            if sprite.pymunk_shape.body.position.y < 0:
                # Remove balls from physics space
                self.space.remove(sprite.pymunk_shape, sprite.pymunk_shape.body)
                # Remove balls from physics list
                sprite.kill()

        # Update physics
        # Use a constant time step, don't use delta_time
        # See "Game loop / moving time forward"
        # http://www.pymunk.org/en/latest/overview.html#game-loop-moving-time-forward
        self.space.step(1 / 60.0)

        # If we are dragging an object, make sure it stays with the mouse. Otherwise
        # gravity will drag it down.
        if self.shape_being_dragged is not None:
            self.shape_being_dragged.shape.body.position = self.last_mouse_position
            self.shape_being_dragged.shape.body.velocity = 0, 0

        # Move sprites to where physics objects are
        for sprite in self.sprite_list:
            sprite.center_x = sprite.pymunk_shape.body.position.x
            sprite.center_y = sprite.pymunk_shape.body.position.y
            sprite.angle = math.degrees(sprite.pymunk_shape.body.angle)

        # Save the time it took to do this.
        self.processing_time = timeit.default_timer() - start_time


def main():
    MyGame(SCREEN_WIDTH, SCREEN_HEIGHT)

    arcade.run()


if __name__ == "__main__":
    main()