Time for action – animating objects with NumPy and Pygame

We will load an image and use NumPy again to define a clockwise path around the screen.

  1. Create a Pygame clock as follows:
    clock = pygame.time.Clock()
  2. As part of the source code accompanying this book, there should be a picture of a head. Load this image and move it around on the screen:
    img = pygame.image.load('head.jpg')
  3. Define some arrays to hold the coordinates of the positions, where we would like to put the image during the animation. Since we will move the object, there are four logical sections of the path: right, down, left, and up. Each of these sections will have 40 equidistant steps. Initialize all the values in the sections to 0:
    steps = np.linspace(20, 360, 40).astype(int)
right = np.zeros((2, len(steps)))
down = np.zeros((2, len(steps)))
left = np.zeros((2, len(steps)))
up = np.zeros((2, len(steps)))
  4. It's straight-forward to set the coordinates of the positions of the image. However, there is one tricky bit to notice—the [::-1] notation leads to reversing the order of the array elements:
    right[0] = steps
right[1] = 20

down[0] = 360
down[1] = steps

left[0] = steps[::-1]
left[1] = 360

up[0] = 20
up[1] = steps[::-1]
  5. We can join the path sections, but before doing this, transpose the arrays with the T operator because they are not aligned properly for concatenation:
    pos = np.concatenate((right.T, down.T, left.T, up.T))
  6. In the main event loop, let the clock tick at a rate of 30 frames per second:
       clock.tick(30)

    A screenshot of the moving head is as follows:

    Time for action – animating objects with NumPy and Pygame

    You should be able to watch a movie of this animation at https://www.youtube.com/watch?v=m2TagGiq1fs, and it is also part of the code bundle (animation.mp4).

    The code of this example uses almost everything we have learnt so far, but should still be simple enough to understand:

    import pygame, sys
from pygame.locals import *
import numpy as np

pygame.init()
clock = pygame.time.Clock()
screen = pygame.display.set_mode((400, 400))

pygame.display.set_caption('Animating Objects')
img = pygame.image.load('head.jpg')

steps = np.linspace(20, 360, 40).astype(int)
right = np.zeros((2, len(steps)))
down = np.zeros((2, len(steps)))
left = np.zeros((2, len(steps)))
up = np.zeros((2, len(steps)))

right[0] = steps
right[1] = 20

down[0] = 360
down[1] = steps

left[0] = steps[::-1]
left[1] = 360

up[0] = 20
up[1] = steps[::-1]

pos = np.concatenate((right.T, down.T, left.T, up.T))
i = 0

while True: 
   # Erase screen
   screen.fill((255, 255, 255))

   if i >= len(pos):
      i = 0

   screen.blit(img, pos[i])
   i += 1

   for event in pygame.event.get():
      if event.type == QUIT:
         pygame.quit()
         sys.exit()

   pygame.display.update()
   clock.tick(30)

What just happened?

We learned a bit about animation in this section. The most important concept we learned about is the clock. The following table describes the new functions we used:

Function

Description

pygame.time.Clock()

This creates a game clock.

clock.tick(30)

This function executes a tick of the game clock. Here, 30 is the number of frames per second.

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