2D Graphics in Java

1
2D Graphics in Java

• COMP53
• Nov 14, 2007

2
Applets and Applications

• Java applications are stand-alone programs
• start execution with main()
• runs in JVM directly under the OS
• Java applets are browser programs
• start in class derived from JApplet
• event driven
• runs in JVM within the browser

3
Basic Applet
// Java core packages import java.awt. // Java
extension packages import javax.swing. public
class BlankGraphicsApplet extends JApplet
public void paint(Graphics g) // call
superclass's paint method (paints background)
super.paint(g) // Here's where we'd put
// application specific drawing instructions

4
Embedding Applet in Web Page
lthtmlgt ltapplet code"BlankGraphicsApplet.class"
width"600" height"400"gt lt/appletgt lt/htmlgt
5
Basic Graphics Application
import java.awt. import java.awt.event. import
javax.swing. public class BlankGraphicsFrame
extends JFrame public BlankGraphicsFrame()
super("Blank Graphics Frame")
setSize(600, 400) show() public void
paint(Graphics g) super.paint(g) //
Here's where we'd put application specific
drawing instructions public static void
main(String args) BlankGraphicsFrame
application new BlankGraphicsFrame()
application.setDefaultCloseOperation(JFrame.EXIT_O
N_CLOSE )
6
When to paint()?

• System calls paint, usually for one of the
  following reasons
• The component is first made visible on the
  screen.
• The component is resized.
• The component has damage that needs to be
  repaired. For example, a covering window has been
  moved.
• The application calls paint, because its
  internal state has changed.
• a button press triggers change in graphics
• animated objects move or change

7
Basics of Drawing

• Drawing commands are methods of the Graphics
  object passed to paint()
• Coordinates are from top left of window

x increase to right
y increase downward
8
Selecting a Drawing Color

• predefined color
• g.setColor(Color.red)
• orange, pink, cyan, magenta, yellow, black,
  white, gray, lightGray, darkGray, red, green,
  blue
• RGB defined color
• g.setColor(new Color(200,20,250))
• red, green and blue in range 0 to 255
• RGB defined color
• g.setColor(new Color(0.7,0.1,0.8))
• red, green and blue in range 0.0 to 1.0

9
Basic Shapes

• rectangles and ovals
• (x1,y1) is upper left corner of shape
• g.drawRect(x1,y1,width,height)rectangle outline
• g.fillRect(x1,y1,width, height)solid rectangle
• g.drawOval(x1,y1,width,height)oval outline
• g.fillOval(x1,y1,width, height)solid oval
• g.drawLine(x1,y1,x2,y2)line from (x1, y1) to
  (x2,y2)

10
Text

• select fontg.setFont(new Font(Arial,
  Font.BOLD, 12))font name, font attributes, font
  size
• draw textg.drawString(Print This!, 20,
  40)string to draw, (x1,y1) top left postion