Source Code for Module rats.tween

 1  """ 
 2  Motion tween equations. 
 3  """ 
 4  #  Easing Equations v1.5 
 5  #  May 1, 2003 
 6  #  (c) 2003 Robert Penner, all rights reserved.  
 7  #  This work is subject to the terms in  
 8  #  http://www.robertpenner.com/easing_terms_of_use.html.   
 9  #   
10  #  These tweening functions provide different flavors of  
11  #  math-based motion under a consistent API.  
12  #   
13  #  Types of easing: 
14  #   
15  #         Linear 
16  #         Quadratic 
17  #         Cubic 
18  #         Quartic 
19  #         Quintic 
20  #         Sinusoidal 
21  #         Exponential 
22  #         Circular 
23  #         Elastic 
24  #         Back 
25  #         Bounce 
26  # 
27  #  Changes: 
28  #  1.5 - added bounce easing 
29  #  1.4 - added elastic and back easing 
30  #  1.3 - tweaked the exponential easing functions to make endpoints exact 
31  #  1.2 - inline optimizations (changing t and multiplying in one step) 
32  #        -- thanks to Tatsuo Kato for the idea 
33  #   
34  #  Discussed in Chapter 7 of  
35  #  Robert Penner's Programming Macromedia Flash MX 
36  #  (including graphs of the easing equations) 
37  #   
38  #  http://www.robertpenner.com/profmx 
39  #  http://www.amazon.com/exec/obidos/ASIN/0072223561/robertpennerc-20 
40  # 
41   
42  LINEAR_TWEEN = 1 
43   
44 -class Tween(object): 
45      """ 
46      Motion tween tool. 
47       
48      """ 
49 -    def __init__(self, start_val, end_val, duration, current_time,  
50              kind=LINEAR_TWEEN): 
51          # TODO: use time from pygame of os ? 
52          # self.t = current_time # current time 
53          self.b = start_val # beginning value 
54          self.c = end_val - start_val # change in value 
55          self.d = duration # duration 
56          self.kind = kind 
57       
58 -    def tick(self, current_time): 
59          """ 
60          Simple wrapper for easing methods. 
61           
62          All the easing methods take those arguments : 
63          t: current time 
64          b: beginning value 
65          c: change in value 
66          d: duration 
67          """ 
68          method = self.linear_tween 
69          if self.kind == LINEAR_TWEEN: 
70              method = self.linear_tween 
71          return method(float(current_time), self.b, self.c, self.d) 
72   
73 -    def linear_tween(self, t, b, c, d): 
74          """ 
75          simple linear tweening - no easing 
76          """ 
77          return c * (t / d) + b 
78   
79  if __name__ == '__main__': 
80      print "this test will tween from 0 to 100 in steps of 10" 
81      kind = LINEAR_TWEEN 
82      start_val = 0.0 
83      end_val = 100.0 
84      duration = 10.0 
85      current_time = 0.0 
86      tween = Tween(start_val, end_val, duration, current_time, kind) 
87      for t in range(11): 
88          print tween.tick(t) 
89