#----------------------------------------------------------------------
# Program to bounce a centered square around the canvas.
#
# Copyright (C) March 30, 2018 -- Dr. William T. Verts
#----------------------------------------------------------------------

import time            # Library of time routines (like time.sleep)

#----------------------------------------------------------------------
# Paint a square centered at <Xc,Yc> with side radius R.  Note the
# default parameters for the colors.  This function can be called as
# follows:
#      addSquare(Canvas, Xc, Yc, green, blue)     # Override both
#      addSquare(Canvas, Xc, Yc, green)           # Override Interior
#      addSquare(Canvas, Xc, Yc)                  # Defaults for both
#----------------------------------------------------------------------

def addSquare (Canvas, Xc, Yc, R, Interior=white, Exterior=black):
    Diameter = 2 * R
    addRectFilled(Canvas, Xc-R, Yc-R, Diameter, Diameter, Interior)
    addRect      (Canvas, Xc-R, Yc-R, Diameter, Diameter, Exterior)
    return
    
#----------------------------------------------------------------------
# Main program
#----------------------------------------------------------------------

def Main():
    W = 600
    H = 500
    Canvas = makeEmptyPicture(W,H)
    
    X = W / 2                                       # Start in the middle
    Y = H / 2                                       # of the canvas
    
    R = 50                                          # Size of box
    
    XDirection = 1                                  # Start moving to the
    YDirection = 1                                  # SouthEast
    
    while True:                                     # Infinite loop
        addRectFilled(Canvas, 0, 0, W, H, white)    # Can also use setAllPixelsToAColor
        addSquare(Canvas, X, Y, R, yellow, red)     # Paint the square
        repaint(Canvas)                             # Update the view
        time.sleep(0.01)                            # Do nothing for 0.01 seconds
        
        X = X + XDirection                          # Move the box
        Y = Y + YDirection                          #
        
        if X+R >= W: XDirection = -1                # Change direction if the
        if X-R <= 0: XDirection = +1                # box hits one of the
        if Y+R >= H: YDirection = -1                # boundary walls
        if Y-R <= 0: YDirection = +1                #
        
    return                                          # Never executed