Graphics: Drawing Fundamentals

1
Graphics Drawing Fundamentals

• Dr. Tim Margush
• University of Akron

2
Goals

• Perform simple drawing tasks in Java

3
Frames

• A Frame is the container for an application's GUI
• GUI Graphical User Interface
• Frame is a class in java.awt providing a title
  bar and a border
• JFrame is a class in javax.swing extending Frame
  adding support for JFC/Swing components

4
Instantiating JFrames

• JFrame jf new JFrame("Sample Frame Title")
• jf.setSize(200, 300)
• jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)
  
• jf.setVisible(true)

• A Frame (JFrame) has properties for its
• title (passed via constructor or setTitle method)
• size (width and height)
• location (default location used, setLocation(x,y)
• behavior (usually exits application when closed)
• visibility (starts hidden)

5
Adding Content to JFrames

• Graphical content is displayed in the JFrame's
  content pane
• A drawing component is added to this pane using
  the add method
• jf.add(someComponent)
• .add(someComponent) adds a Component object to
  the Container.

6
Graphical Hierarchy
Component
A small subset of the hierarchy tree
Container
Button
CheckBox
JComponent
Panel
JPanel
JScrollPane
JOptionPane
Applet
JApplet
7
Drawing on Components

• Use a JPanel for a basic graphics canvas
• Graphics commands are executed from the
  paintComponent method
• paintComponent is called by the graphics system
  when it appears the canvas needs to be refreshed
• public void paintComponent(Graphics g)
• The java.awt.Graphics object is provided by the
  system when this method is called
• You NEVER directly call this method

8
java.awt.Graphics

• The Graphics object represents the canvas where
  drawing can occur
• Methods include
• drawArc, drawOval, fillRect, drawPolygon
• fillArc, fillOval, fillRect, fillPolygon
• drawImage, drawLine
• setColor
• setFont, drawString

9
java.awt.Graphics2D

• A subclass of Graphics adding new and improved
  methods
• public void paintComponent(Graphics g)
• //g is actually a Graphics2D object when
• // supplied by a swing component
• Graphics2D g2 (Graphics2D) g //cast
• Graphics2D objects have methods
• draw, drawString, fill, draw3DRect, setPaint,
  setStroke, setBackground,

10
Coordinate System
(0,0)
Increasing X coords
72 dpi

• Coordinate system
• Top left is (0,0)
• X increases to the right
• Y increases downward
• (over, down)
• Methods exist to alter the transform used to
  specify coordinates and to draw text, shapes, and
  images

Increasing Y coords
11
Customizing a JPanel

• public class NameComponent extends JPanel
• public void paintComponent(Graphics g)
• super.paintComponent(g) //allows proper
  initialization of the canvas
• Graphics2D g2 (Graphics2D) g //if using 2D
  extensions
• //Add your custom drawing commands here
• g2.setFont(new Font("SansSerif", Font.ITALIC,
  24))
• g2.drawString("Java Jerry", 20, 40)

• jf.add(new NameComponent())
• jf.setVisible(true)

12
Drawing Lines

• public class LineSample extends JPanel
• public void paintComponent(Graphics g)
• super.paintComponent(g)
• int w getWidth() //gets the width of the
  panel itself
• int h getHeight() //gets the height of the
  panel itself
• //Add your custom drawing commands here
• g.drawLine(0,0,w,h)
• g.drawLine(0,h/2,w,h/2)
• g.drawLine(w/2,0,w/2,h)

13
Drawing Shapes

• public class ShapeSample extends JPanel
• public void paintComponent(Graphics g)
• super.paintComponent(g)
• Graphics2D g2 (Graphics2D) g
• //Add your custom drawing commands here
• g2.setColor(Color.RED)
• g2.fill(new Rectangle(20, 50, 100, 30))
• g2.setColor(Color.BLUE)
• g2.draw(new Rectangle(10, 75, 25, 100))