Java Graphics Stuart Hansen 11603

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Java GraphicsStuart Hansen11/6/03
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Whats Wrong with OpenGL

• Graphics not GUI
• No real support of text boxes, buttons, etc.
• Procedural - not OOP
• No sense of attaching frame to polygon, etc.
• No inheritance or polymorphism
• Open Inventor OOP extension to OpenGL
• Java OpenGL bridge
• http//www.sgi.com/newsroom/press_releases/2003/ju
  ly/sgisun_opengl.html

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Java Graphics

• Component Based
• AWT vs. Swing
• We will discuss Swing
• Uses Model View Controller after a fashion
• Model holds the data
• View presents the data
• Control changes the data

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Swing Classes

• JFrame is the window
• setSize(), setLocation(), setVisible()
• getContentPane()
• JButton, JLabel, JTextBox, etc.
• JPanel is the generic component, useful if we
  are going to do graphics as you are studying them.

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Steps to Drawing in JPanel

• Inherit from ComponentUI
• Override the paint method
• public void paint (Graphics g, JComponent jc)
• Define but never explicitly call
• Call JPanels setUI method with instance of our
  class.

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Graphics and Graphics2D

• Graphics2D is subclass and is almost always used.
• We cast Graphics to Graphics2D
• Coordinate system (0,0) is upper left of JPanel
• Lots of draw and fill methods
• Lots of translate and rotate methods.

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Example 1 A Clock

• Clock outline is lines, rectangles and ovals
• Clock hands are lines, but rotated
• Clock pendulum swings by doing a rotation

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Math for Hour Hand

• 2p is one rotation.
• 12 hours is one rotation.
• hourTheta hour/12 2p hour p / 6
• Add a fudge factor for minutes so hand moves
  smoothly.

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Example 2 Set Cards

• Four properties for each card
• Color, number, symbol and shading
• 3 possibilities for each property
• Goal is to have elegant way of drawing the cards

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Who needs OOP?

• Game of Set
• http//www.setgame.com
• Simple rules
• Find cards that form a Set
• Each card has four features
• Color, Symbol Number and Shading
• A Set consists of three cards where each feature
  agrees on all cards or disagrees on all cards.

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This is a Set
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This is not a Set
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Object Oriented Design of Set Cards

• Each attribute is an object
• No need for if
• E.g. No need for
• if (card.shading.equals(squiggle)) . .
• Shading has all needed methods in it.

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Flyweight Design Pattern

• Only one instance of each class!
• Allows us to compare using
• Limits number of objects to 12 rather than
  hundreds

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Back to Graphics

• Cards paint method pseudocode
• setColor(color)
• for each location
• shape.draw(shading)
• Color, location, shape and shading are the
  attributes

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Shape uses polymorphism

• Ovals, Diamonds and Squiggles each know how to
  draw themselves
• Shape interface specifies that each shape has a
  draw method. Thats it.

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Shading specifies the fill pattern

• Solid cards use foreground color
• Open cards use the background color
• Striped cards use a Texture Paint pattern

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Drawbacks of Java Graphics

• Java will always be slower than C
• Java lacks much of the OpenGL functionality
• Texturing, lighting, etc.
• Java requires non-standard library to do 3D
  Graphics
• Complex class hierarchies are harder to learn
  than procedural API (or are they?)