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Comments on Assignments

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Embed data and code in a class. Create basic behaviours of multiple objects moving and ... Want to be able to move around without bumping into obstacles ... – PowerPoint PPT presentation

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Title: Comments on Assignments

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Comments on Assignments

Everyone did very well
Report writing needs more work
Jumping scale
Update first then draw

3
\\ aims

By the end of the session you will be able to
Use Loops and Arrays to control the behaviour of
multiple objects
Create a class
Embed data and code in a class
Create basic behaviours of multiple objects
moving and interaction with each other

4
\\ Objects and Behaviour

Lots of our programs involve things that move
around and interact
Often we want lots of these things
How do we handle many interacting objects?

5
\\ Loops and arrays

The answer is with loops and arrays
Gone over last week as well as in java

6
\\ Instructions and data

A program consists of 2 things
Instructions
The commands we give
e.g. size(200,200) x xy
Data
The variables, state of a program
e.g. int x 100

7
\\ Instructions and data

Instructions are typed into a program in a
sequence from top to bottom
They are executed one by one
But the real power comes when you change the order

8
\\ Instructions and data

Instructions are typed into a program in a
sequence from top to bottom
They are executed one by one
But the real power comes when you change the
order
If statements select particular commands to
execute

9
\\ Instructions and data

Instructions are typed into a program in a
sequence from top to bottom
They are executed one by one
But the real power comes when you change the
order
Loops execute commands multiple times

10
\\ Loops

Loops let you do a set of commands many times
while only typing them once
More importantly, you dont need to know how many
times until you get to the loop

11
\\ Arrays

You also want to do the same thing with data
Have many repeated data item
Give them a single name
Arrays

12
\\ Arrays
X2
0
1
2
3
4
13
\\ Arrays and Loops

Arrays and Loops go very well together
There isnt much use to having arrays unless you
can step through them and do stuff to each
element
Loops do just that

14
\\ Arrays and Loops

int X new int30
for (int i 0 i lt X.length i)
Xi i3

15
\\ Objects and Behaviour

Lots of our programs involve things that move
around and interact
Often we want lots of these things
How do we handle many interacting objects?

16
\\ Objects and Behaviour

You can use Arrays to store data about our
objects
e.g. position, velocity
Loops to create their behaviour

// the number of balls
int ballNumber 20
// The data we need to know about balls
// This is the "State" of the program
// As we have multiple balls we need to hold
their state
// we use a set of array with a posiion for each
ball
// the size of a ball
int ballSize 10
// the x and y position
float xPos, yPos
// the velocity
float xVel, yVel

void setup()
size(500, 500)
// create all the arrays
xPos new floatballNumber
yPos new floatballNumber
xVel new floatballNumber
yVel new floatballNumber
// put data in them
// create a random position and velocity for
each
for (int i 0 i lt ballNumber i)
// create a random position on the screen
// make sure all positions are at least
// ballSize from the edge of the screen

void draw()
background(255)
// update all the balls
for (int i 0 i lt ballNumber i)
// update the position of the ball
// by adding on the velocity
xPosi xVeli
yPosi yVeli
// draw the ball
strokeWeight(4)
ellipse(xPosi, yPosi, ballSize,
ballSize)

20
\\ Objects and Behaviour

Doesnt seem quite right
xPos, xVel etc. are all features of a ball
Dont they some how belong together, not in
separate arrays?
Shouldnt we somewhere have something that
represents a ball?
That is where classes come in.

21
\\ Classes

Classes are a way of putting data that belong
together in the same place
They can represent real world things like balls
You use them to create your own types

22
\\ Classes

Rather than having an array of positions and an
array of velocities
You can have an array of balls
A ball contains a position and a velocity

23
\\ Classes

A class is like a new type (int, float etc.)
It represents a generic class like Balls
A particular ball is an object, e.g. a variable
of type Ball

// create a class to represent a ball
class Ball
// all the data for the ball is now
// stored in the class
float xPos, yPos
float xVel, yVel
float Size
Ball ball new Ball()
ball.xPos 100

25
\\ new and dot

To create an object of a class you use the
keyword new
You can put the result in a variable
To access a variable (member) of a class, you use
a dot .

// create a class to represent a ball
class Ball
// all the data for the ball is now
// stored in the class
float xPos, yPos
float xVel, yVel
float Size
Ball ball new Ball()
ball.xPos 100

27
\\ Classes

We can now create an array of Ball objects
Use them in our simulation instead of individual
arrays
Much tidier

// Now we only need one array to hold all the
balls
Ball balls
void setup()
size(500, 500)
// create an array of balls
balls new BallballNumber
// Add new items to the array
for (int i 0 i lt balls.length i)
ballsi new Ball()
// set up the data for the ball
ballsi.Size 10

void draw()
background(255)
// update an draw the balls
for (int i 0 i lt balls.length i)
ballsi.xPos ballsi.xVel
ballsi.yPos ballsi.yVel
// draw the ball
strokeWeight(4)
ellipse(ballsi.xPos, ballsi.yPos,
ballsi.Size, ballsi.Size)

30

\\ Exercises

Create a class for a ball
Using that class create a program where multiple
balls move around bouncing off the edges of the
screen
Extra can you create more complex behaviour?
Extra can you make the balls interact with each
other?

31

\\ Classes

Im still not that happy
Weve now put all the data for a ball together
But there are also instructions that relate to
balls
e.g. moving and drawing
Shouldnt they go in the class as well?
Yes Methods

32

\\ Blocks of code

Instructions are grouped together into blocks
Curly brackets create blocks
E.g. Loops, if statements, functions

if (i lt 100)
// this is one block
else
// this is another
for (int i 0 i lt 100 i)
// this is a third block

34

\\ Functions

You can think of these as block of code that you
can call in other places
A way of being able to reuse blocks of code
A bit like a variable allows us to reuse data

int ballx 10
int bally 10
// a function
void drawBall()
ellipse(ballx, bally, 10, 10)
// another function
void setup()
for (int i 0 i lt 100 i)
ballx 10
drawBall()

36

\\ Methods

A method is a function that is attached to a
class
It allows us to put both data and instructions
together in a single class
The behaviour of the class becomes part of the
class

class Ball
float xPos, yPos, xVel, yVel
float Size
// a constructor
Ball()
// Update the position of the ball
void update()
// draw the ball on screen
void draw()

38

\\ Methods

You can add whatever methods you like to a class
You call methods using the dot . notation just
like member variables

39

\\ Constructors

Classes have special methods called
constructors
They are called when the class is created
A bit like a setup method for a class
They have the same name as the class

40

\\ Constructors

Constructors are used to set up all the data in
the class
Provide initial values to all the variables

class Ball
float xPos, yPos, xVel, yVel
float Size
// a constructor
Ball()
// set the value of the size
Size 10.0
// set up the initial positions to random
values
xPos random(Size, width-Size)
yPos random(Size, height-Size)
// set up random velocities
xVel random(-2, 2)
yVel random(-2, 2)

42

\\ Constructors

All you need to do now is create an object of the
class
The variables now set themselves up in the
constructor

// Now we only need one array to hold all the
balls
Ball balls
void setup()
size(500, 500)
// create an array of balls
balls new BallballNumber
// Add new items to the array
for (int i 0 i lt balls.length i)
ballsi new Ball()

44

\\ Simulating behaviour

A good way of simulating behaviour is to have a
set of 3 methods
Constructor
Update
Draw

45

\\ Simulating behaviour

A good way of simulating behaviour is to have a
set of 3 methods
Constructor
Sets up all the variables
Update
Draw

46

\\ Simulating behaviour

A good way of simulating behaviour is to have a
set of 3 methods
Constructor
Update
Updates the variables each frame
e.g. changes the position
Draw

47

\\ Simulating behaviour

A good way of simulating behaviour is to have a
set of 3 methods
Constructor
Update
Draw
Draw the object to the screen

class Ball
float xPos, yPos, xVel, yVel
float Size
// a constructor
Ball()
// Update the position of the ball
void update()
xPos xVel
yPos yVel
// draw the ball on screen
void draw()

49

\\ Simulating behaviour

Update and draw can then be called from the main
draw function

void draw()
background(255)
// update and draw the balls
for (int i 0 i lt balls.length i)
ballsi.update()
ballsi.draw()

51

\\ Exercises

Take your existing code and rewrite it using
methods

52
\\ aims

By the end of the session you will be able to
Use Loops and Arrays to control the behaviour of
multiple objects
Create a class
Embed data and code in a class
Create basic behaviours of multiple objects
moving and interaction with each other

53
\\ Behaviours

Now wed like our objects to do some more
interesting things
Im going to go through a bunch of behaviours
Seek
Flee
Obstacle avoidance

54
\\ Seek

Head towards an object
Each frame we update the velocity so that we are
getting closer to a target
Add a small factor in the direction of the target

55
\\ Seek

How do we work out the direction between two
objects?
Subtract their positions
xDir target.ball.xPos
yDir target.ball.yPos

56
\\ Seek

Subtract the balls position from the targets
position
ball.vel ball.vel (target.pos - ball.pos)
This would take us there in one step
But dont want it to move so fast, so only use a
fraction
ball.vel ball.vel (target.pos - ball.pos)/c
Where c is a constant

57
\\ Flee

The opposite of seek
Run away from the target
ball.vel ball.vel - (target.pos - ball.pos)/c

58
\\ Obstacle Avoidance

Want to be able to move around without bumping
into obstacles
Could just flee from all obstacles, but you dont
want to avoid ones that are very far away
Make the change inversely proportional to the
distance squared

59
\\ Obstacle Avoidance

How do we work out the distance
Pythagoras Theorem

h
y
x
h2 x2 y2
60
\\ Obstacle Avoidance

h2 x2 y2
Distance
h sqrt(x2 y2)
Direction
x/h, y/h

61
\\ Obstacle Avoidance

dirx obstacle.posx ball.posx
h sqrt(dirxdirx dirydiry)
dirx dirx/h
dirx disp/h
ball.velx ball.velx (dirx)/(hh)

62
\\ Obstacle Avoidance

Lots of other ways of doing it

63

\\ Exercises

Implement Seek behaviour (to the mouse?)
Create an obstacle class
Get your objects to avoid the obstacles

64
\\ aims

By the end of the session you will be able to
Use Loops and Arrays to control the behaviour of
multiple objects
Create a class
Embed data and code in a class
Create basic behaviours of multiple objects
moving and interaction with each other

65
Craig Reynolds - flocking

The first behavioural simulation
Simulates the behaviour of flocks of birds
(biods), schools of fish or herds of animals
Extensively used in films and other applications
Flocks, herds and schools a distributed
behavioural model Craig Reynolds SIGGRAPH 1987

66
Boids

Craig Reynolds work was an early aspect of the
artificial life field
He observed the behaviour of real flocks of birds
and tried to figure out rules of their behaviour
The resulting rules are surprisingly simple

67
Boids

Separation
Alignment
Cohesion

68
Boids

Separation
Steer away from flockmates that are very close

69
Boids

Alignment
Match direction to the average direction of
nearby flockmates

70
Boids

Cohesion
Move towards the centre of mass of nearby
flockmates

71
Boids Action Selection

Need some way of combining the behaviours
They have a priority
Separation
Alignment
Cohesion
But it isnt absolute

72
Craig Reynolds - flocking

Emergent Behaviour
These simple rules produce surprising results
Here is a flock splitting to avoid an obstacle
They recombine afterwards, just like a real flock

73
\\ Assignment

In this assignment you will be creating a
flocking simulation
1. (20 )
Create a program in which a number of object move
around the screen with different velocities and
bounce of the edges of the window. Use a class to
represent the objects.

74
\\ Assignment

2. (40 )
Make your objects flock using Reynoldss 3 rules
of flocking
Separation
Alignment
Cohesion

75
\\ Assignment

3. (10 )
As well as flocking make the objects move towards
the mouse pointer so that you can control the
movement of the flock using the mouse.
4. (10 )
10 further marks will be added for creative
extensions to the program.

76
\\ Assignment

5. (20 )
Submit
A written report on your implementation,
explaining what method you used for each stage.
2 images of your program running for each stage,
before and after moving the mouse.
The code files, with comments, explaining each
part of the code.

77
\\ More classes