velocity_control.py

__author__ = 'wanderson'
# control the velocity of a ball using the arrow keys

import simpleguitk as simplegui

# Initialize globals
WIDTH = 600
HEIGHT = 400
BALL_RADIUS = 20

ball_pos = [WIDTH / 2, HEIGHT / 2]
vel = [0, 0]

# define event handlers
def draw(canvas):
    # Update ball position
    ball_pos[0] += vel[0]
    ball_pos[1] += vel[1]

    # Draw ball
    canvas.draw_circle(ball_pos, BALL_RADIUS, 2, "Red", "White")

def keydown(key):
    acc = 1
    if key==simplegui.KEY_MAP["left"]:
        vel[0] -= acc
    elif key==simplegui.KEY_MAP["right"]:
        vel[0] += acc
    elif key==simplegui.KEY_MAP["down"]:
        vel[1] += acc
    elif key==simplegui.KEY_MAP["up"]:
        vel[1] -= acc

    print ball_pos, vel

# create frame
frame = simplegui.create_frame("Velocity ball control", WIDTH, HEIGHT)

# register event handlers
frame.set_draw_handler(draw)
frame.set_keydown_handler(keydown)

# start frame
frame.start()