DUE: Thursday, 24 September, in class
Create an interactive program with dynamically-added, moving objects.
The basic behavior is: whenever the user clicks a mouse button, or moves the mouse with a button pressed, a new object appears at the mouse location. The object should have random color and/or movement.
The motion should have some discernable pattern to it - the direction could change over time; the objects could start following the mouse; they could orbit the center of the window; etc.
Other possible features: use different mouse buttons to add different shapes (or ones with different behavior); animate the objects colors; have objects disappear after a certain amount of time; ...
We often would like the behavior of a program to change or be unpredictable - to not be exactly the same every time we run it.
In other cases, randomness helps eliminate unwanted artifacts, such as obvious, excessively regular or repeated patterns. These include patterns in the appearance and in the movement of objects.
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Things that can be randomized include:
Randomness is added to programs by using random numbers. These are generated by random number functions.
Python has a package called random.
Two of the functions it provides are:
In C, the standard random number functions are:
Random numbers can come in different distributions - how frequently the various numbers occur.
e.g. rolling a fair die many times will yield roughly
the same number of 1s, 2s, 3s, 4s, 5s, and 6s.
A loaded die can produce one number more frequently.
random() & uniform()
return uniform distributions - each possible number is equally
likely to be returned.
If you call the function a large number of times, then you
can expect each possible number to be returned about (but not exactly)
the same number of times.
(Flipping a coin 1,000,000 times, you would expect to get roughly
500,000 heads and 500,000 tails.)
This plot is from calling int(random() * 100) 100,000 times. It shows how many times each of the possible values (from 0 to 99) was returned.
Sometimes we want a different distribution.
A common distribution is the bell curve (or gaussian distribution). In this distribution, one small range of numbers is returned more frequently than others, with values further from the center of the distribution returned less and less frequently.
The Python function random.gauss(center, deviation) returns random numbers in a gaussian distribution.
The first argument (center) is the central number that the return
values will be clustered around. The second argument (deviation)
is the standard deviation of the distribution - this measures how broad the
bell curve is; roughly 2/3 of all returned values will be within +/- deviation
of the center value.
Example: a gaussian distribution lets you place objects randomly, but clustered about a center.
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Python's random.shuffle(list) randomly re-orders a list (in place).
>>> letters = ['a', 'b', 'c', 'd', 'e', 'f'] >>> letters ['a', 'b', 'c', 'd', 'e', 'f'] >>> random.shuffle(letters) >>> letters ['f', 'e', 'd', 'c', 'b', 'a'] >>> random.shuffle(letters) >>> letters ['c', 'b', 'a', 'd', 'e', 'f']
Classes are a central feature of object-oriented programming (OOP)
A class contains both data and functions to operate on that data
Classes are used to encapsulate related data & code - parts of the program that support one specific aspect of the program
Objects are "instances" of a class
A class in Python is created with the class command
Functions in a Python class always have as their first argument a pointer to the object calling the function (typically named self)
One important function is the "constructor", which in Python is always named __init__
class Circle:
def __init__(self, x, y, radius, color):
self.x = x
self.y = y
self.radius = radius
self.color = color
def draw(self):
glColor3fv(self.color)
glBegin(GL_TRIANGLE_FAN)
glVertex2f(self.x, self.y)
for i in range(0,30):
glVertex2f(self.x + cos(radians(i*12.0)) * radius,
self.y + sin(radians(i*12.0)) * radius)
glEnd()
c = Circle(0, 0, 5, [1,0,0])
