Java: Animation

1
JavaAnimation

• Chris North
• cs3724 HCI

2
Animation?

• Changing graphics over time
• Examples
• cartoons
• Clippy, agents/assistants
• Hour glass
• Save dohicky
• Progress bar
• Copy file
• Amits pulsating plot

3
Purvi

• Algorithm Animation

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Java Graphics Review

• Extend JPanel
• Override paintComponent( ) method
• public class MyPanel extends JPanel
• public void paintComponent(Graphics g)
• super.paintComponent(g)
• Graphics2D g2 (Graphics2D)g
• // my graphics here
• g2.drawString("Hello World", 10, 10)

5
Ticker
6
Animating the ticker text

• Keep repainting graphics using different x
• public class MyPanel extends JPanel
• int x
• public void paintComponent(Graphics g)
• super.paintComponent(g)
• Graphics2D g2 (Graphics2D)g
• // my graphics here
• g2.drawString("Hello World", x, 10)

7
Animation Loop

• Update x location (member variable)
• Repaint
• While(true) //infinite loop
• x x 1
• repaint() //calls paintComponent()
• Thread.sleep(10) //slow down animation
• Problem?

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Multi-Threading

• Loop prevents other parts of code from executing
• User events pile up
• Multiple threads let multiple methods execute
  simultaneously (multi-tasking)
• Threads lightweight processes, shared memory

Main thread User interaction
Anim thread Update graphics
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Java Threads

• implement Runnable interface
• Override run( ) method
• Put animation loop here
• new Thread(runnable)
• Thread.start( )
• Calls runnable.run( )in new thread

Runnable run( )
My Panel
Thread start( )
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Simplifying

• MyPanel implements Runnable

Runnable run( )
My Panel
My Panel Runnable run( )
Thread start( )
Thread start( )
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Threaded Ticker

• public class MyPanel extends JPanel implements
  Runnable
• int x 100
• Thread mythread
• public MyPanel() // constructor
• mythread new Thread(this)
• mythread.start()
• public void run()
• while(true) // animation loop
• x x 5
• repaint()
• Thread.sleep(100)
• public void paintComponent(Graphics g)
• super.paintComponent(g)
• Graphics2D g2 (Graphics2D)g

or in button code that starts animation
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Stopping a Thread

• Stop animation loop with a flag
• mythread null will cleanup thread object
• Boolean runMyAnimation
• While(runMyAnimation) //flag stops loop
• x x 5
• repaint() //calls paintComponent()
• Thread.sleep(100) //slow down animation

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Controlling Animation Speed

• While(true)
• x x 5 //animation step size
• repaint()
• Thread.sleep(100) //delay between steps

Milliseconds 1000 1 second
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Animation Summary

• In a secondary thread
• Make changes to global state
• Repaint
• Sleep delay
• Repeat
• Use double buffering as needed

15
JBuilder Example