Transcript Java Graphics Stuart Hansen 11/6/03

Java Graphics
Stuart Hansen
11/6/03
What’s 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/july/sgisun_opengl.html
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
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.
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 JPanel’s setUI method with instance
of our class.
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.
Example 1 – A Clock
• Clock outline is lines, rectangles and ovals
• Clock hands are lines, but rotated
• Clock pendulum swings by doing a
rotation
Math for Hour Hand
• 2π is one rotation.
• 12 hours is one rotation.
• hourTheta = hour/12 * 2π = hour * π / 6
• Add a fudge factor for minutes so hand
moves smoothly.
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
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.
This is a Set
This is not a Set
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.
Flyweight Design Pattern
• Only one instance of each class!
– Allows us to compare using ==
• Limits number of objects to 12 rather than
hundreds
Back to Graphics
• Card’s paint method pseudocode:
setColor(color)
for each location
shape.draw(shading)
• Color, location, shape and shading are the
attributes
Shape uses polymorphism
• Ovals, Diamonds and Squiggles each
know how to draw themselves
• Shape interface specifies that each shape
has a draw method. That’s it.
Shading specifies the fill pattern
• Solid cards use foreground color
• Open cards use the background color
• Striped cards use a Texture Paint pattern
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?)