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If you are of a certain age, you’ll remember those ancient technological devices called DVD players. When not playing DVDs, they would display a diagonally traveling DVD logo that bounced off the edges of the screen. This program simulates this colorful DVD logo by making it change direction each time it hits an edge. We’ll also keep track of how many times a logo hits a corner of the screen. This creates an interesting visual animation to look at, especially for the magical moment when a logo lines up perfectly with a corner.
You can’t run this program from your integrated development environment (IDE) or editor because it uses the bext module. Therefore, it must be run from the Command Prompt or Terminal in order to display correctly. You can find more information about the bext module at https://pypi.org/project/bext/.
When you run bouncingdvd.py, the output will look like Figure 5-1.
Figure 5-1: The diagonally moving DVD logos of the bouncingdvd.py program
You may remember Cartesian coordinates from your math class in school. In programming, the x-coordinate represents an object’s horizontal position and the y-coordinate represents its vertical position, just like in mathematics. However, unlike in mathematics, the origin point (0, 0) is in the upper-left corner of the screen, and the y-coordinate increases as you go down. The x-coordinate increases as the object moves right, just like in mathematics. Figure 5-2 shows the coordinate system for your screen.
Figure 5-2: The origin point (0, 0) is in the upper left of the screen, while the x- and y-coordinates increase going right and down, respectively.
The bext module’s goto() function works the same way: calling bext.goto(0, 0) places the text cursor at the top left of the terminal window. We represent each bouncing DVD logo using a Python dictionary with the keys 'color', 'direction', 'x', and 'y'. The values for the 'x' and 'y' are integers representing the logo’s position in the window. Since these values get passed to bext.goto(), increasing them will move the logo right and down, while decreasing them will move the logo left and up.
1. """Bouncing DVD Logo, by Al Sweigart [email protected]
2. A bouncing DVD logo animation. You have to be "of a certain age" to
3. appreciate this. Press Ctrl-C to stop.
4.
5. NOTE: Do not resize the terminal window while this program is running.
6. This code is available at https://nostarch.com/big-book-small-python-programming
7. Tags: short, artistic, bext"""
8.
9. import sys, random, time
10.
11. try:
12. import bext
13. except ImportError:
14. print('This program requires the bext module, which you')
15. print('can install by following the instructions at')
16. print('https://pypi.org/project/Bext/')
17. sys.exit()
18.
19. # Set up the constants:
20. WIDTH, HEIGHT = bext.size()
21. # We can't print to the last column on Windows without it adding a
22. # newline automatically, so reduce the width by one:
23. WIDTH -= 1
24.
25. NUMBER_OF_LOGOS = 5 # (!) Try changing this to 1 or 100.
26. PAUSE_AMOUNT = 0.2 # (!) Try changing this to 1.0 or 0.0.
27. # (!) Try changing this list to fewer colors:
28. COLORS = ['red', 'green', 'yellow', 'blue', 'magenta', 'cyan', 'white']
29.
30. UP_RIGHT = 'ur'
31. UP_LEFT = 'ul'
32. DOWN_RIGHT = 'dr'
33. DOWN_LEFT = 'dl'
34. DIRECTIONS = (UP_RIGHT, UP_LEFT, DOWN_RIGHT, DOWN_LEFT)
35.
36. # Key names for logo dictionaries:
37. COLOR = 'color'
38. X = 'x'
39. Y = 'y'
40. DIR = 'direction'
41.
42.
43. def main():
44. bext.clear()
45.
46. # Generate some logos.
47. logos = []
48. for i in range(NUMBER_OF_LOGOS):
49. logos.append({COLOR: random.choice(COLORS),
50. X: random.randint(1, WIDTH - 4),
51. Y: random.randint(1, HEIGHT - 4),
52. DIR: random.choice(DIRECTIONS)})
53. if logos[-1][X] % 2 == 1:
54. # Make sure X is even so it can hit the corner.
55. logos[-1][X] -= 1
56.
57. cornerBounces = 0 # Count how many times a logo hits a corner.
58. while True: # Main program loop.
59. for logo in logos: # Handle each logo in the logos list.
60. # Erase the logo's current location:
61. bext.goto(logo[X], logo[Y])
62. print(' ', end='') # (!) Try commenting this line out.
63.
64. originalDirection = logo[DIR]
65.
66. # See if the logo bounces off the corners:
67. if logo[X] == 0 and logo[Y] == 0:
68. logo[DIR] = DOWN_RIGHT
69. cornerBounces += 1
70. elif logo[X] == 0 and logo[Y] == HEIGHT - 1:
71. logo[DIR] = UP_RIGHT
72. cornerBounces += 1
73. elif logo[X] == WIDTH - 3 and logo[Y] == 0:
74. logo[DIR] = DOWN_LEFT
75. cornerBounces += 1
76. elif logo[X] == WIDTH - 3 and logo[Y] == HEIGHT - 1:
77. logo[DIR] = UP_LEFT
78. cornerBounces += 1
79.
80. # See if the logo bounces off the left edge:
81. elif logo[X] == 0 and logo[DIR] == UP_LEFT:
82. logo[DIR] = UP_RIGHT
83. elif logo[X] == 0 and logo[DIR] == DOWN_LEFT:
84. logo[DIR] = DOWN_RIGHT
85.
86. # See if the logo bounces off the right edge:
87. # (WIDTH - 3 because 'DVD' has 3 letters.)
88. elif logo[X] == WIDTH - 3 and logo[DIR] == UP_RIGHT:
89. logo[DIR] = UP_LEFT
90. elif logo[X] == WIDTH - 3 and logo[DIR] == DOWN_RIGHT:
91. logo[DIR] = DOWN_LEFT
92.
93. # See if the logo bounces off the top edge:
94. elif logo[Y] == 0 and logo[DIR] == UP_LEFT:
95. logo[DIR] = DOWN_LEFT
96. elif logo[Y] == 0 and logo[DIR] == UP_RIGHT:
97. logo[DIR] = DOWN_RIGHT
98.
99. # See if the logo bounces off the bottom edge:
100. elif logo[Y] == HEIGHT - 1 and logo[DIR] == DOWN_LEFT:
101. logo[DIR] = UP_LEFT
102. elif logo[Y] == HEIGHT - 1 and logo[DIR] == DOWN_RIGHT:
103. logo[DIR] = UP_RIGHT
104.
105. if logo[DIR] != originalDirection:
106. # Change color when the logo bounces:
107. logo[COLOR] = random.choice(COLORS)
108.
109. # Move the logo. (X moves by 2 because the terminal
110. # characters are twice as tall as they are wide.)
111. if logo[DIR] == UP_RIGHT:
112. logo[X] += 2
113. logo[Y] -= 1
114. elif logo[DIR] == UP_LEFT:
115. logo[X] -= 2
116. logo[Y] -= 1
117. elif logo[DIR] == DOWN_RIGHT:
118. logo[X] += 2
119. logo[Y] += 1
120. elif logo[DIR] == DOWN_LEFT:
121. logo[X] -= 2
122. logo[Y] += 1
123.
124. # Display number of corner bounces:
125. bext.goto(5, 0)
126. bext.fg('white')
127. print('Corner bounces:', cornerBounces, end='')
128.
129. for logo in logos:
130. # Draw the logos at their new location:
131. bext.goto(logo[X], logo[Y])
132. bext.fg(logo[COLOR])
133. print('DVD', end='')
134.
135. bext.goto(0, 0)
136.
137. sys.stdout.flush() # (Required for bext-using programs.)
138. time.sleep(PAUSE_AMOUNT)
139.
140.
141. # If this program was run (instead of imported), run the game:
142. if __name__ == '__main__':
143. try:
144. main()
145. except KeyboardInterrupt:
146. print()
147. print('Bouncing DVD Logo, by Al Sweigart')
148. sys.exit() # When Ctrl-C is pressed, end the program.
After entering the source code and running it a few times, try making experimental changes to it. The comments marked with (!) have suggestions for small changes you can make. On your own, you can also try to figure out how to do the following:
NUMBER_OF_LOGOS to increase the number of bouncing logos on the screen.PAUSE_AMOUNT to speed up or slow down the logos.Try to find the answers to the following questions. Experiment with some modifications to the code and rerun the program to see what effect the changes have.
WIDTH, HEIGHT = bext.size() on line 20 to WIDTH, HEIGHT = 10, 5?DIR: random.choice(DIRECTIONS) on line 52 with DIR: DOWN_RIGHT?'Corner bounces:' text not appear on the screen?cornerBounces = 0 on line 57?